View source for Lysozyme

{{Short description|Antimicrobial enzyme produced by animals}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{Distinguish|Lysosome|Lysosomal enzymes|Lysin}}
{{Use dmy dates|date=August 2020}}
{{infobox enzyme
| Name       = Lysozyme
| EC_number  = 3.2.1.17
| CAS_number = 9001-63-2
| GO_code    = 0003796
}}
{{Infobox protein family 
| image = Lysozymecrystals1.png
| caption = Lysozyme crystals stained with [[methylene blue]].
|Name=Glycoside hydrolase, family 22, lysozyme
|InterPro=IPR000974
|PRINTS=PR00137
}}
'''Lysozyme''' ({{EnzExplorer|3.2.1.17}}, '''muramidase, ''N''-acetylmuramide glycanhydrolase'''; systematic name '''peptidoglycan ''N''-acetylmuramoylhydrolase''') is an [[antimicrobial]] enzyme produced by animals that forms part of the [[innate immune system]]. It is a [[glycoside hydrolase]] that catalyzes the following process:

: Hydrolysis of (1→4)-β-linkages between ''N''-acetylmuramic acid and ''N''-acetyl-<small>D</small>-glucosamine residues in a peptidoglycan and between ''N''-acetyl-<small>D</small>-glucosamine residues in chitodextrins

Peptidoglycan is the major component of [[gram-positive bacteria]]l cell wall.<ref name=":0">{{cite book | vauthors = Manchenko GP | title = Handbook of Detection of Enzymes on Electrophoretic Gels |year = 1994 | publisher = CRC Press | location = Boca Raton, Fla. | isbn = 978-0-8493-8935-1 | page = [https://archive.org/details/handbookofdetect0000manc/page/223 223] | chapter-url = https://www.google.com/search?q=Hydrolysis+of+%281-%3E4%29-beta-linkages+between+N-acetylmuramic+acid+and+N-acetyl-D-glucosamine+residues+in+a+peptidoglycan+and+between+N-acetyl-D-glucosamine+residues+in+chitodextrins#tbs=cdr:1%2Ccd_min:1900%2Ccd_max:2006&tbm=bks&q=Hydrolysis+linkages+between+N-acetylmuramic+acid+N-acetyl-D-glucosamine+residues+in+a+peptidoglycan+and+between+N-acetyl-D-glucosamine+residues+in+chitodextrins&* | chapter = Lysozyme | url-access = registration | url = https://archive.org/details/handbookofdetect0000manc/page/223 }}</ref> This hydrolysis in turn compromises the integrity of bacterial cell walls causing [[lysis]] of the bacteria.

Lysozyme is abundant in [[secretion]]s including [[tears]], [[saliva]], [[human milk]], and [[mucus]]. It is also present in [[cytoplasmic]] granules of the [[macrophages]] and the [[polymorphonuclear neutrophil]]s (PMNs). Large amounts of lysozyme can be found in [[egg white]]. C-type lysozymes are closely related to [[alpha-lactalbumin|α-lactalbumin]] in sequence and structure, making them part of the same [[glycoside hydrolase family 22]].<ref>{{cite web| vauthors = Williams S, Vocadlo D |title= Glycoside hydrolase family 22 |url= https://www.cazypedia.org/index.php/Glycoside_Hydrolase_Family_22 |website=Cazypedia|access-date=11 April 2017}}</ref> In humans, the C-type lysozyme enzyme is encoded by the ''LYZ'' gene.<ref name="Yoshimura_1988">{{cite journal | vauthors = Yoshimura K, Toibana A, Nakahama K | title = Human lysozyme: sequencing of a cDNA, and expression and secretion by Saccharomyces cerevisiae | journal = Biochemical and Biophysical Research Communications | volume = 150 | issue = 2 | pages = 794–801 | date = January 1988 | pmid = 2829884 | doi = 10.1016/0006-291X(88)90461-5 }}</ref><ref name="Peters_1989">{{cite journal | vauthors = Peters CW, Kruse U, Pollwein R, Grzeschik KH, Sippel AE | title = The human lysozyme gene. Sequence organization and chromosomal localization | journal = European Journal of Biochemistry | volume = 182 | issue = 3 | pages = 507–516 | date = July 1989 | pmid = 2546758 | doi = 10.1111/j.1432-1033.1989.tb14857.x | doi-access = free }}</ref>

Hen egg white lysozyme is thermally stable, with a [[melting point]] reaching up to 72&nbsp;°C at pH 5.0.<ref>{{cite journal | vauthors = Venkataramani S, Truntzer J, Coleman DR | title = Thermal stability of high concentration lysozyme across varying pH: A Fourier Transform Infrared study | journal = Journal of Pharmacy & Bioallied Sciences | volume = 5 | issue = 2 | pages = 148–153 | date = April 2013 | pmid = 23833521 | pmc = 3697194 | doi = 10.4103/0975-7406.111821 | doi-access = free }}</ref> However, lysozyme in human milk loses activity very quickly at that temperature.<ref>{{cite journal | vauthors = Chandan RC, Shahani KM, Holly RG | title = Lysozyme Content of Human Milk | journal = Nature | volume = 204 | issue = 4953 | pages = 76–77 | date = October 1964 | pmid = 14240122 | doi = 10.1038/204076a0 | s2cid = 4215401 | bibcode = 1964Natur.204...76C }}</ref> Hen egg white lysozyme maintains its activity in a large range of pH (6–9).<ref>{{cite web | url = https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Datasheet/7/l7651dat.pdf | title = Lysozyme, Product information | publisher = Sigma-Aldrich }}</ref> Its [[isoelectric point]] is 11.35.<ref>{{cite web | url = https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Datasheet/7/l7651dat.pdf | title = Lysozyme, Product information | publisher = Sigma-Aldrich }}</ref> The isoelectric point of human milk lysozyme is 10.5–11.<ref>{{cite journal | vauthors = Parry RM, Chandan RC, Shahani KM | title = Isolation and characterization of human milk lysozyme | journal = Archives of Biochemistry and Biophysics | volume = 130 | issue = 1 | pages = 59–65 | date = March 1969 | pmid = 5778672 | doi = 10.1016/0003-9861(69)90009-5 | doi-access = free }}</ref>

== Function and mechanism ==

The [[enzyme]] functions by hydrolyzing glycosidic bonds in [[peptidoglycan]]s. The enzyme can also break [[glycosidic bond]]s in [[chitin]], although not as effectively as true [[chitinase]]s.<ref>{{cite journal | vauthors = Skujiņś J, Puķite A, McLaren AD | title = Adsorption and reactions of chitinase and lysozyme on chitin | journal = Molecular and Cellular Biochemistry | volume = 2 | issue = 2 | pages = 221–228 | date = December 1973 | pmid = 4359167 | doi = 10.1007/BF01795475 | s2cid = 27906558 }}</ref>

[[File:Mecanism of action for Lysozyme.svg|thumb|320px|Overview of the reaction catalysed by lysozyme]]Lysozyme's active site binds the [[peptidoglycan]] molecule in the prominent cleft between its two domains. It attacks peptidoglycans (found in the cell walls of bacteria, especially [[Gram-positive bacteria]]), its natural [[Substrate (chemistry)#Biochemistry|substrate]], between [[N-Acetylmuramic acid|''N''-acetylmuramic acid]] (NAM) and the fourth carbon atom of [[N-acetylglucosamine]] (NAG).{{cn|date=July 2024}}

Shorter [[Carbohydrate|saccharides]] like tetrasaccharide have also shown to be viable substrates but via an intermediate with a longer chain.<ref>{{cite journal | vauthors = Sharon N | title = The chemical structure of lysozyme substrates and their cleavage by the enzyme | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 167 | issue = 1009 | pages = 402–415 | date = April 1967 | pmid = 4382803 | doi = 10.1098/rspb.1967.0037 | s2cid = 31794497 | bibcode = 1967RSPSB.167..402S }}</ref> Chitin has also been shown to be a viable lysozyme substrate. Artificial substrates have also been developed and used in lysozyme.<ref>{{cite book | vauthors = Höltje JV | chapter = Lysozyme Substrates | title = Lysozymes: Model Enzymes in Biochemistry and Biology | volume = 75 | pages = 105–110 | date = 1996-01-01 | pmid = 8765297 | doi = 10.1007/978-3-0348-9225-4_7 | isbn = 978-3-0348-9952-9 | series = Experientia Supplementum | doi-broken-date = 2 November 2024 }}</ref>

=== Mechanism ===

==== Phillips ====
The Phillips mechanism proposed that the enzyme's catalytic power came from both steric strain on the bound substrate and electrostatic stabilization of an [[Oxocarbenium|oxo-carbenium]] intermediate. From X-ray crystallographic data, Phillips proposed the active site of the enzyme, where a hexasaccharide binds. The lysozyme distorts the fourth sugar (in the D or -1 subsite) in the hexasaccharide into a half-chair conformation. In this stressed state, the glycosidic bond is more easily broken.<ref>{{cite journal | vauthors = Blake CC, Johnson LN, Mair GA, North AC, Phillips DC, Sarma VR | title = Crystallographic studies of the activity of hen egg-white lysozyme | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 167 | issue = 1009 | pages = 378–388 | date = April 1967 | pmid = 4382801 | doi = 10.1098/rspb.1967.0035 | s2cid = 35094695 | bibcode = 1967RSPSB.167..378B }}</ref> An ionic intermediate containing an [[Oxocarbenium|oxo-carbenium]] is created as a result of the glycosidic bond breaking.<ref name="Application of secondary alpha-deut">{{cite journal | vauthors = Dahlquist FW, Rand-Meir T, Raftery MA | title = Application of secondary α-deuterium kinetic isotope effects to studies of enzyme catalysis. Glycoside hydrolysis by lysozyme and β-glucosidase | journal = Biochemistry | volume = 8 | issue = 10 | pages = 4214–4221 | date = October 1969 | pmid = 5388150 | doi = 10.1021/bi00838a045 }}</ref> Thus distortion causing the substrate molecule to adopt a strained conformation similar to that of the [[transition state]] will lower the energy barrier of the reaction.<ref name="McKenzie_1991">{{cite journal | vauthors = McKenzie HA, White FH | title = Lysozyme and α-lactalbumin: structure, function, and interrelationships | journal = Advances in Protein Chemistry | volume = 41 | pages = 173–315 | year = 1991 | pmid = 2069076 | doi = 10.1016/s0065-3233(08)60198-9 | isbn = 978-0-12-034241-9 }}</ref>

The proposed oxo-carbonium intermediate was speculated to be electrostatically stabilized by aspartate and glutamate residues in the active site by [[Arieh Warshel]] in 1978. The electrostatic stabilization argument was based on comparison to bulk water, the reorientation of water dipoles can cancel out the stabilizing energy of charge interaction. In Warshel's model, the enzyme acts as a super-solvent, which fixes the orientation of ion pairs and provides super-[[solvation]] (very good stabilization of ion pairs), and especially lower the energy when two ions are close to each other.<ref>{{cite journal | vauthors = Warshel A | title = Energetics of enzyme catalysis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 75 | issue = 11 | pages = 5250–5254 | date = November 1978 | pmid = 281676 | pmc = 392938 | doi = 10.1073/pnas.75.11.5250 | doi-access = free | bibcode = 1978PNAS...75.5250W }}</ref>

The [[rate-determining step]] (RDS) in this mechanism is related to formation of the [[Oxocarbenium|oxo-carbenium]] intermediate. There were some contradictory results to indicate the exact RDS. By tracing the formation of product ([[4-Nitrophenol|p-nitrophenol]]), it was discovered that the RDS can change over different temperatures, which was a reason for those contradictory results. At a higher temperature the RDS is formation of glycosyl enzyme intermediate and at a lower temperature the breakdown of that intermediate.<ref>{{cite journal | vauthors = Weber JP, Fink AL | title = Temperature-dependent change in the rate-limiting step of β-glucosidase catalysis | journal = The Journal of Biological Chemistry | volume = 255 | issue = 19 | pages = 9030–9032 | date = October 1980 | pmid = 6773958 | doi = 10.1016/S0021-9258(19)70521-3 | doi-access = free }}</ref>
[[File:Lysozyme glycosyl covalent intermediate.gif|thumb|Covalent intermediate of lysozyme enzyme, with covalent bond in black and experimental evidence as blue mesh.<ref>{{Cite web|url=http://proteopedia.org/wiki/index.php/Lysozyme#Covalent_intermediate_and_product_complex|title = Hen Egg-White (HEW) Lysozyme - Proteopedia, life in 3D}}</ref>]]

==== Covalent mechanism ====
[[File:LysozymeIntermediates copy.png|thumb|400px|Substrates in Vocadlo's experiment]]
In an early debate in 1969, Dahlquist proposed a covalent mechanism for lysozyme based on [[kinetic isotope effect]],<ref name="Application of secondary alpha-deut"/> but for a long time the ionic mechanism was more accepted. In 2001, a revised mechanism was proposed by Vocadlo via a covalent but not ionic intermediate. Evidence from [[Electrospray ionization|ESI]]-[[Mass spectrometry|MS]] analysis indicated a covalent intermediate. A 2-fluoro substituted substrate was used to lower the reaction rate and accumulate an intermediate for characterization.<ref name="Vocadlo_2001">{{cite journal | vauthors = Vocadlo DJ, Davies GJ, Laine R, Withers SG | title = Catalysis by hen egg-white lysozyme proceeds via a covalent intermediate | journal = Nature | volume = 412 | issue = 6849 | pages = 835–838 | date = August 2001 | pmid = 11518970 | doi = 10.1038/35090602 | s2cid = 205020153 | bibcode = 2001Natur.412..835V | url = https://eprints.whiterose.ac.uk/131/1/daviesgj1.pdf }}</ref> The amino acid side-chains glutamic acid 35 (Glu35) and aspartate 52 (Asp52) have been found to be critical to the activity of this enzyme. Glu35 acts as a proton donor to the glycosidic bond, cleaving the C-O bond in the substrate, whereas Asp52 acts as a [[nucleophile]] to generate a glycosyl enzyme intermediate. The Glu35 reacts with water to form hydroxyl ion, a stronger [[nucleophile]] than water, which then attacks the glycosyl enzyme intermediate, to give the product of hydrolysis and leaving the enzyme unchanged.<ref name="isbn0-495-11912-12">{{cite book | title = Biochemistry | vauthors = Grisham CM, Garrett RH | publisher = Thomson Brooks/Cole | year = 2007 | isbn = 978-0-495-11912-8 | location  =Australia | pages = 467–9 | chapter = Chapter 14: Mechanism of enzyme action | chapter-url = https://books.google.com/books?id=W4o_5YGqfYsC&q=lysozyme%20mechanism%20of%20action%20glu-35%20asp-52&pg=PA468}}</ref> This type of covalent mechanism for enzyme catalysis was first proposed by [[Daniel E. Koshland Jr.|Koshland]].<ref>{{cite journal | vauthors = Koshland DE | date = November 1953 | title = Stereochemistry and the Mechanism of Enzymatic Reactions | journal = Biological Reviews | volume = 28 | issue = 4 | pages = 416–436 | doi = 10.1111/j.1469-185X.1953.tb01386.x | s2cid = 86709302 | url = https://digital.library.unt.edu/ark:/67531/metadc1255185/ }}</ref>

More recently, quantum mechanics/ molecular mechanics (QM/MM) [[molecular dynamics]] simulations have been using the crystal of HEWL and predict the existence of a covalent intermediate.<ref name = "Bowman_2008">{{cite journal | vauthors = Bowman AL, Grant IM, Mulholland AJ | title = QM/MM simulations predict a covalent intermediate in the hen egg white lysozyme reaction with its natural substrate | journal = Chemical Communications | issue = 37 | pages = 4425–4427 | date = October 2008 | pmid = 18802578 | doi = 10.1039/b810099c }}</ref> Evidence for the ESI-MS and X-ray structures indicate the existence of covalent intermediate, but primarily rely on using a less active mutant or non-native substrate. Thus, QM/MM molecular dynamics provides the unique ability to directly investigate the mechanism of wild-type HEWL and native substrate. The calculations revealed that the covalent intermediate from the covalent mechanism is ~30 kcal/mol more stable than the ionic intermediate from the Phillips mechanism.<ref name="Bowman_2008" /> These calculations demonstrate that the ionic intermediate is extremely energetically unfavorable and the covalent intermediates observed from experiments using less active mutant or non-native substrates provide useful insight into the mechanism of wild-type HEWL.{{cn|date=July 2024}}
[[File:JBSlysozymemechanism copy2.jpg|thumb|Two Possible Mechanisms of Lysozyme]]

=== Inhibition ===
[[Imidazole]] derivatives can form a [[charge-transfer complex]] with some residues (in or outside active center) to achieve a competitive inhibition of lysozyme.<ref>{{cite journal | vauthors = Swan ID | title = The inhibition of hen egg-white lysozyme by imidazole and indole derivatives | journal = Journal of Molecular Biology | volume = 65 | issue = 1 | pages = 59–62 | date = March 1972 | pmid = 5063023 | doi = 10.1016/0022-2836(72)90491-3 }}</ref> In [[Gram-negative bacteria]], the [[lipopolysaccharide]] acts as a non-competitive inhibitor by highly favored binding with lysozyme.<ref>{{cite journal | vauthors = Ohno N, Morrison DC | title = Lipopolysaccharide interaction with lysozyme. Binding of lipopolysaccharide to lysozyme and inhibition of lysozyme enzymatic activity | journal = The Journal of Biological Chemistry | volume = 264 | issue = 8 | pages = 4434–4441 | date = March 1989 | pmid = 2647736 | doi = 10.1016/S0021-9258(18)83761-9 | doi-access = free }}</ref>{{further|Glycoside hydrolase}}

=== Non-enzymatic action ===
Despite that the muramidase activity of lysozyme has been supposed to play the key role for its antibacterial properties, evidence of its non-enzymatic action was also reported. For example, blocking the catalytic activity of lysozyme by mutation of critical amino acid in the active site (52-[[Aspartic acid|Asp]] -> 52-[[Serine|Ser]]) does not eliminate its antimicrobial activity.<ref>{{cite journal | vauthors = Ibrahim HR, Matsuzaki T, Aoki T | title = Genetic evidence that antibacterial activity of lysozyme is independent of its catalytic function | journal = FEBS Letters | volume = 506 | issue = 1 | pages = 27–32 | date = September 2001 | pmid = 11591365 | doi = 10.1016/S0014-5793(01)02872-1 | s2cid = 21593262 | doi-access = free | bibcode = 2001FEBSL.506...27I }}</ref> The lectin-like ability of lysozyme to recognize bacterial carbohydrate antigen without lytic activity was reported for tetrasaccharide related to [[lipopolysaccharide]] of ''[[Klebsiella pneumoniae]]''.<ref>{{cite journal | vauthors = Zhang R, Wu L, Eckert T, Burg-Roderfeld M, Rojas-Macias MA, Lütteke T, Krylov VB, Argunov DA, Datta A, Markart P, Guenther A, Norden B, Schauer R, Bhunia A, Enani MA, Billeter M, Scheidig AJ, Nifantiev NE, Siebert HC | title = Lysozyme's lectin-like characteristics facilitates its immune defense function | journal = Quarterly Reviews of Biophysics | volume = 50 | pages = e9 | date = January 2017 | pmid = 29233221 | doi = 10.1017/S0033583517000075 | doi-access = free }}</ref> Also, lysozyme interacts with antibodies and [[T-cell receptors]].<ref>{{cite book | vauthors = Grivel JC, Smith-Gill SJ | title = Lysozyme: Antigenic structure as defined by antibody and T cell responses |year = 1996 | publisher = CRC Press | isbn = 978-0-8493-9225-2 | pages = 91–144 }}</ref>

=== Enzyme conformation changes ===
Lysozyme exhibits two conformations: an open active state and a closed inactive state. The catalytic relevance was examined with single walled [[carbon nanotube]]s (SWCN) field effect transistors (FETs), where a singular lysozyme was bound to the SWCN FET.<ref>{{cite journal | vauthors = Choi Y, Moody IS, Sims PC, Hunt SR, Corso BL, Perez I, Weiss GA, Collins PG | title = Single-molecule lysozyme dynamics monitored by an electronic circuit | journal = Science | volume = 335 | issue = 6066 | pages = 319–324 | date = January 2012 | pmid = 22267809 | pmc = 3914775 | doi = 10.1126/science.1214824 | bibcode = 2012Sci...335..319C }}</ref> Electronically monitoring the lysozyme showed two conformations, an open active site and a closed inactive site. In its active state lysozyme is able to [[Processivity|processively]] hydrolyze its substrate, breaking on average 100 bonds at a rate of 15 per second. In order to bind a new substrate and move from the closed inactive state to the open active state requires two conformation step changes, while inactivation requires one step.{{cn|date=July 2024}}

=== Superfamily ===
The conventional C-type lysozyme is part of a larger group of structurally and mechanistically related enzymes termed the ''lysozyme [[Protein superfamily|superfamily]]''. This family unites GH22 C-type ("chicken") lysozymes with plant chitinase [[Glycoside hydrolase family 19|GH19]], G-type ("goose") lysozyme [[Glycoside hydrolase family 23|GH23]], V-type ("viral") lysozyme [[Glycoside hydrolase family 24|GH24]] and the chitosanase [[Glycoside hydrolase family 46|GH46]] families. The lysozyme-type nomenclature only reflects the source a type is originally isolated from and does not fully reflect the taxonomic distribution.<ref>{{cite journal | vauthors = Wohlkönig A, Huet J, Looze Y, Wintjens R | title = Structural relationships in the lysozyme superfamily: significant evidence for glycoside hydrolase signature motifs | journal = PLOS ONE | volume = 5 | issue = 11 | pages = e15388 | date = November 2010 | pmid = 21085702 | pmc = 2976769 | doi = 10.1371/journal.pone.0015388 | doi-access = free | bibcode = 2010PLoSO...515388W }}</ref> For example, humans and many other mammals have two G-type lysozyme genes, [[LYG1]] and [[LYG2]].<ref>{{cite journal | vauthors = Irwin DM | title = Evolution of the vertebrate goose-type lysozyme gene family | journal = BMC Evolutionary Biology | volume = 14 | issue = 1 | pages = 188 | date = August 2014 | pmid = 25167808 | pmc = 4243810 | doi = 10.1186/s12862-014-0188-x | bibcode = 2014BMCEE..14..188I | doi-access = free }}</ref>

== Role in disease and therapy ==
{{#invoke:Infobox_gene|getTemplateData|QID=Q14862873}}
Lysozyme is part of the innate immune system. Reduced lysozyme levels have been associated with [[bronchopulmonary dysplasia]] in newborns.<ref name="pmid1640295">{{cite journal | vauthors = Revenis ME, Kaliner MA | title = Lactoferrin and lysozyme deficiency in airway secretions: association with the development of bronchopulmonary dysplasia | journal = The Journal of Pediatrics | volume = 121 | issue = 2 | pages = 262–270 | date = August 1992 | pmid = 1640295 | doi = 10.1016/S0022-3476(05)81201-6 | url = https://zenodo.org/record/1259643 }}</ref> Piglets fed with human lysozyme milk can recover from diarrheal disease caused by ''E. coli'' faster. The concentration of lysozyme in human milk is 1,600 to 3,000 times greater than the concentration in livestock milk. Human lysozyme is more active than hen egg white lysozyme. A [[Transgenesis|transgenic]] line of goats (with a [[Founder effect#Founder mutation|founder]] named "Artemis") were developed to produce milk with human lysozyme to protect children from diarrhea if they can't get the benefits of human breastfeeding.<ref name="pmid23516474">{{cite journal | vauthors = Cooper CA, Garas Klobas LC, Maga EA, Murray JD | title = Consuming transgenic goats' milk containing the antimicrobial protein lysozyme helps resolve diarrhea in young pigs | journal = PLOS ONE | volume = 8 | issue = 3 | pages = e58409 | year = 2013 | pmid = 23516474 | pmc = 3596375 | doi = 10.1371/journal.pone.0058409 | doi-access = free | bibcode = 2013PLoSO...858409C }}</ref><ref name="Artemis_2016">{{cite web | vauthors = Molteni M | title = Spilled Milk | work = Case Studies: News Features | publisher = Undark: Truth, Beauty, Science | date = 30 June 2016 | url = http://undark.org/article/gmo-goats-lysozyme-uc-davis-diarrhea/ | access-date = 2017-01-12 }}</ref>

Since lysozyme is a natural form of protection from [[Gram-positive bacteria|Gram-positive]] pathogens like ''[[Bacillus]]'' and ''[[Streptococcus]]'',<ref>{{cite book | vauthors = Nester EW, Anderson DG, Roberts CE, Nester MT | title = Microbiology: A Human Perspective |year = 2007 | publisher = McGraw-Hill Higher Education | location = Boston, Mass. | isbn = 978-0-07-110706-8 | edition = 5th }}</ref> it plays an important role in immunology of infants in human milk feeding.<ref>{{cite journal | vauthors = Chandra RK | title = Immunological aspects of human milk | journal = Nutrition Reviews | volume = 36 | issue = 9 | pages = 265–272 | date = September 1978 | pmid = 362248 | doi = 10.1111/j.1753-4887.1978.tb07393.x }}</ref> Whereas the skin is a protective barrier due to its dryness and acidity, the [[conjunctiva]] (membrane covering the eye) is, instead, protected by secreted enzymes, mainly lysozyme and [[defensin]]. However, when these protective barriers fail, [[conjunctivitis]] results.{{cn|date=July 2024}}

In certain cancers (especially myelomonocytic leukemia) excessive production of lysozyme by cancer cells can lead to toxic levels of lysozyme in the blood.  High lysozyme blood levels can lead to kidney failure and low blood potassium, conditions that may improve or resolve with treatment of the primary malignancy.{{cn|date=July 2024}}

Serum lysozyme is much less specific for diagnosis of sarcoidosis than serum angiotensin converting enzyme; however, since it is more sensitive, it is used as a marker of sarcoidosis disease activity and is suitable for disease monitoring in proven cases.<ref name="pmid10192763">{{cite journal | vauthors = Tomita H, Sato S, Matsuda R, Sugiura Y, Kawaguchi H, Niimi T, Yoshida S, Morishita M | title = Serum lysozyme levels and clinical features of sarcoidosis | journal = Lung | volume = 177 | issue = 3 | pages = 161–167 | year = 1999 | pmid = 10192763 | doi = 10.1007/pl00007637 | s2cid = 3999327 }}</ref>

== Chemical synthesis ==

The first chemical synthesis of a lysozyme protein was attempted by Prof. George W. Kenner and his group at the University of Liverpool in England.<ref name="pmid19745">{{cite journal | vauthors = Kenner GW | title = The Bakerian lecture. Towards synthesis of proteins | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 197 | issue = 1128 | pages = 237–253 | date = June 1977 | pmid = 19745 | doi = 10.1098/rspb.1977.0068 | s2cid = 170906912 | bibcode = 1977RSPSB.197..237K }}</ref> This was finally achieved in 2007 by Thomas Durek in Steve Kent's lab at the University of Chicago who made a synthetic functional lysozyme molecule.<ref name="pmid17360367">{{cite journal | vauthors = Durek T, Torbeev VY, Kent SB | title = Convergent chemical synthesis and high-resolution x-ray structure of human lysozyme | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 12 | pages = 4846–4851 | date = March 2007 | pmid = 17360367 | pmc = 1829227 | doi = 10.1073/pnas.0610630104 | doi-access = free | bibcode = 2007PNAS..104.4846D }}</ref>

== Other applications ==
Lysozyme crystals have been used to grow other functional materials for catalysis and biomedical applications.<ref>{{cite journal | vauthors = Wei H, Wang Z, Zhang J, House S, Gao YG, Yang L, Robinson H, Tan LH, Xing H, Hou C, Robertson IM, Zuo JM, Lu Y | title = Time-dependent, protein-directed growth of gold nanoparticles within a single crystal of lysozyme | journal = Nature Nanotechnology | volume = 6 | issue = 2 | pages = 93–97 | date = February 2011 | pmid = 21278750 | doi = 10.1038/nnano.2010.280 | bibcode = 2011NatNa...6...93W }}</ref><ref>{{cite journal | vauthors = Sanghamitra NJ, Ueno T | title = Expanding coordination chemistry from protein to protein assembly | journal = Chemical Communications | volume = 49 | issue = 39 | pages = 4114–4126 | date = May 2013 | pmid = 23211931 | doi = 10.1039/C2CC36935D }}</ref><ref>{{cite journal | vauthors = Ueno T | title = Porous protein crystals as reaction vessels | journal = Chemistry: A European Journal | volume = 19 | issue = 28 | pages = 9096–9102 | date = July 2013 | pmid = 23813903 | doi = 10.1002/chem.201300250 }}</ref> Lysozyme is a commonly used enzyme for lysing gram positive bacteria.<ref>{{cite journal | vauthors = Repaske R | title = Lysis of gram-negative bacteria by lysozyme | journal = Biochimica et Biophysica Acta | volume = 22 | issue = 1 | pages = 189–191 | date = October 1956 | pmid = 13373865 | doi = 10.1016/0006-3002(56)90240-2 }}</ref> Due to the unique function of lysozyme in which it can digest the cell wall and causes [[osmotic shock]] (burst the cell by suddenly changing solute concentration around the cell and thus the [[osmotic pressure]]), lysozyme is commonly used in lab setting to release proteins from bacterium [[periplasm]] while the inner membrane remains sealed as vesicles called the [[spheroplast]].<ref>{{Cite book|title=Protein Condensation : Kinetic Pathways to Crystallization and Disease |url= https://archive.org/details/proteincondensat00gunt|url-access=limited| vauthors = Gunton J, Shiryayev A, Pagan DL |location = Cambridge | publisher = Cambridge University Press |year=2007 |isbn= 978-0-511-53532-1 |pages=[https://archive.org/details/proteincondensat00gunt/page/n168 156]–158}}</ref><ref>{{Cite book|title=Fundamental Laboratory Approaches for Biochemistry and Biotechnology | vauthors = Ninfa A, Ballou D, Benore M |publisher=John Wiley |year=2010 |isbn=978-0-470-08766-4 }}</ref>

For example, ''E. coli'' can be lysed using lysozyme to free the contents of the [[periplasm]]ic space. It is especially useful in lab setting for trying to collect the contents of the periplasm.<ref name=":0" /> Lysozyme treatment is optimal at particular temperatures, pH ranges, and salt concentrations. Lysozyme activity increases with increasing temperatures, up to 60 degrees Celsius, with a pH range of 6.0-7.0. The salts present also affect lysozyme treatment, where some assert inhibitory effects, and others promote lysis via lysozyme treatment. Sodium chloride induces lysis, but at high concentrations, it is an active inhibitor of lysis. Similar observations have been seen with the use of potassium salts. Slight variations are present due to differences in bacterial strains.<ref>{{cite journal | vauthors = Salton MR | title = The properties of lysozyme and its action on microorganisms | journal = Bacteriological Reviews | volume = 21 | issue = 2 | pages = 82–100 | date = June 1957 | pmid = 13436356 | pmc = 180888 | doi = 10.1128/MMBR.21.2.82-100.1957 }}</ref> A consequence of the use of lysozyme in extracting recombinant proteins for [[protein crystallization]] is that the crystal may be contaminated with units of lysozyme, producing a physiologically irrelevant combination. In fact, some proteins simply cannot crystalize without such contamination.<ref>{{cite journal | vauthors = Liu W, MacGrath SM, Koleske AJ, Boggon TJ | title = Lysozyme contamination facilitates crystallization of a heterotrimeric cortactin-Arg-lysozyme complex | journal = Acta Crystallographica. Section F, Structural Biology and Crystallization Communications | volume = 68 | issue = Pt 2 | pages = 154–158 | date = February 2012 | pmid = 22297987 | pmc = 3274391 | doi = 10.1107/S1744309111056132 }}</ref><ref>{{cite journal | vauthors = Kincannon WM, Zahn M, Clare R, Lusty Beech J, Romberg A, Larson J, Bothner B, Beckham GT, McGeehan JE, DuBois JL | title = Biochemical and structural characterization of an aromatic ring-hydroxylating dioxygenase for terephthalic acid catabolism | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 119 | issue = 13 | pages = e2121426119 | date = March 2022 | pmid = 35312352 | pmc = 9060491 | doi = 10.1073/pnas.2121426119 | doi-access = free | bibcode = 2022PNAS..11921426K }}</ref>

Furthermore, lysozyme can serve as a tool in the expression of toxic recombinant proteins. Expressing recombinant proteins in BL21(DE3) strains is typically accomplished by the T7-RNA-polymerase. Via IPTG induction, the UV-5 repressor is inhibited, leading to the transcription of the T7-RNA-polymerase and thereby of the protein of interest. Nonetheless, a basal level of the T7-RNA-polymerase is observable even without induction. T7 lysozyme acts as an inhibitor of the T7-RNA-polymerase. Newly invented strains, containing a helper plasmid (pLysS), constitutively co-express low levels of T7 lysozyme, providing high stringency and consistent expression of the toxic recombinant protein.<ref>{{cite journal | vauthors = Pan SH, Malcolm BA | title = Reduced background expression and improved plasmid stability with pET vectors in BL21 (DE3) | journal = BioTechniques | volume = 29 | issue = 6 | pages = 1234–1238 | date = December 2000 | pmid = 11126126 | doi = 10.2144/00296st03 | doi-access = free }}</ref>

== History ==

The antibacterial property of hen egg white, due to the lysozyme it contains, was first observed by Laschtschenko in 1909.<ref name = "Laschtschenko">{{cite journal | vauthors = Laschtschenko P | title = Über die keimtötende und entwicklungshemmende Wirkung Hühnereiweiß |trans-title=On the germ-killing and growth-inhibiting effect of chicken egg albumin | journal = Zeitschrift für Hygiene und Infektionskrankheiten | year = 1909 | volume = 64  | pages = 419–427 | language = de | doi = 10.1007/BF02216170| s2cid = 456259 }}</ref> The bacteria-killing activity of nasal mucus was demonstrated in 1922 by [[Alexander Fleming]], the discoverer of [[penicillin]], who coined the term "lysozyme".<ref>{{cite journal | vauthors = Duckett S | title = Ernest Duchesne and the concept of fungal antibiotic therapy | journal = Lancet | volume = 354 | issue = 9195 | pages = 2068–2071 | date = December 1999 | pmid = 10636385 | doi = 10.1016/S0140-6736(99)03162-1 | s2cid = 206011471 }}</ref> He is reported as saying: "As this substance has properties akin to those of ferments I have called it a 'Lysozyme'."<ref name="Fleming_1922">{{cite journal | vauthors = Fleming A | title = On a remarkable bacteriolytic element found in tissues and secretions  |  journal = [[Proceedings of the Royal Society B]] | volume = 93 | issue = 653 | pages = 306–317 | date = May 1922 | doi = 10.1098/rspb.1922.0023 | jstor=80959| bibcode = 1922RSPSB..93..306F | doi-access = free }}</ref> Fleming went on to show that an enzymic substance was present in a wide variety of secretions and was capable of rapidly lysing (i.e. dissolving) different bacteria, particularly a yellow "coccus"<!--italics?--> that he studied".<ref>{{cite book|title=Advances in Protein Chemistry|url=https://books.google.com/books?id=U1P3a5hjbSAC&pg=PA176|date=13 June 1991|publisher=Academic Press|isbn=978-0-08-058214-6|pages=176–}}</ref>

Lysozyme was first crystallised by [[Edward Abraham]] in 1937, enabling the three-dimensional structure of hen egg white lysozyme to be described by [[David Chilton Phillips]] in 1965, when he obtained the first 2-[[ångström]] (200 [[picometer|pm]]) resolution model via [[X-ray crystallography]].<ref>{{cite journal | vauthors = Blake CC, Koenig DF, Mair GA, North AC, Phillips DC, Sarma VR | title = Structure of hen egg-white lysozyme. A three-dimensional Fourier synthesis at 2 Angstrom resolution | journal = Nature | volume = 206 | issue = 4986 | pages = 757–761 | date = May 1965 | pmid = 5891407 | doi = 10.1038/206757a0 | s2cid = 4161467 }}</ref><ref>{{cite journal | vauthors = Johnson LN, Phillips DC | title = Structure of some crystalline lysozyme-inhibitor complexes determined by X-ray analysis at 6 Angstrom resolution | journal = Nature | volume = 206 | issue = 4986 | pages = 761–763 | date = May 1965 | pmid = 5840126 | doi = 10.1038/206761a0 | s2cid = 10234792 }}</ref> The structure was publicly presented at a [[Royal Institution]] lecture in 1965.<ref name="Johnson1998">{{cite journal | vauthors = Johnson LN | title = The early history of lysozyme | journal = Nature Structural Biology | volume = 5 | issue = 11 | pages = 942–944 | date = November 1998 | pmid = 9808036 | doi = 10.1038/2917 | s2cid = 2629199 }}</ref>
Lysozyme was the second protein structure and the first enzyme structure to be solved via X-ray diffraction methods, and the first enzyme to be fully sequenced that contains all twenty common amino acids.<ref name="Canfield1963">{{cite journal | vauthors = Canfield RE | title = The Amino Acid Sequence of Egg White Lysozyme | journal = The Journal of Biological Chemistry | volume = 238 | issue = 8 | pages = 2698–2707 | date = August 1963 | pmid = 14063294 | doi = 10.1016/S0021-9258(18)67888-3 | doi-access = free }}</ref>
As a result of Phillips' elucidation of the structure of lysozyme, it was also the first enzyme to have a detailed, specific mechanism suggested for its method of catalytic action.<ref>{{cite journal | vauthors = Vernon CA | title = The mechanisms of hydrolysis of glycosides and their revelance [sic] to enzyme-catalysed reactions | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 167 | issue = 1009 | pages = 389–401 | date = April 1967 | pmid = 4382802 | doi = 10.1098/rspb.1967.0036 | s2cid = 12870128 | bibcode = 1967RSPSB.167..389V | jstor = 75680 }}</ref><ref>{{cite journal | vauthors = Rupley JA | title = The binding and cleavage by lysozyme of N-acetylglucosamine oligosaccharides | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 167 | issue = 1009 | pages = 416–428 | date = April 1967 | pmid = 4382804 | doi = 10.1098/rspb.1967.0038 | s2cid = 33906706 | bibcode = 1967RSPSB.167..416R | jstor = 75682 }}</ref><ref>{{cite journal | vauthors = Sharon N | title = The chemical structure of lysozyme substrates and their cleavage by the enzyme | journal = Proceedings of the Royal Society of London. Series B, Biological Sciences | volume = 167 | issue = 1009 | pages = 402–415 | date = April 1967 | pmid = 4382803 | doi = 10.1098/rspb.1967.0037 | s2cid = 31794497 | bibcode = 1967RSPSB.167..402S | jstor = 75681 }}</ref> This work led Phillips to provide an explanation for how [[enzymes]] speed up a chemical reaction in terms of its physical structures. The original mechanism proposed by Phillips was more recently revised.<ref name="Vocadlo_2001"/>

== See also ==
* [[Egg allergy]]
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== References ==
{{Reflist|30em}}

== External links ==
* {{MeshName|Muramidase}}
* [https://web.archive.org/web/20160712061916/http://www.proteopedia.org/wiki/index.php/Hen_Egg-White_(HEW)_Lysozyme Proteopedia.org HEW Lysozyme]
* [https://www.ebi.ac.uk/pdbe/pdbe-kb/proteins/P61626 PDBe-KB] provides an overview of all the structure information available in the PDB for Human Lysozyme C.
* [https://www.ebi.ac.uk/pdbe/pdbe-kb/proteins/P00698 PDBe-KB] provides an overview of all the structure information available in the PDB for Hen egg white Lysozyme C.

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