View source for Thiaminase

{{Short description|Class of enzymes}}
{{Infobox enzyme
| Name = Thiamine pyridinylase
| EC_number = 2.5.1.2
| CAS_number = 9030-35-7
| IUBMB_EC_number = 2/5/1/2
| GO_code = 
| image = 
| width = 
| caption =
}}
{{Infobox enzyme
| Name = Aminopyrimidine aminohydrolase
| EC_number = 3.5.99.2
| GO_code = 0050334
| image = 
| width = 
| caption =
}}
[[Image:Thiamine_structure.svg|thumb|[[Thiamine]]]]
'''Thiaminase''' is an [[enzyme]] that [[metabolism|metabolizes]] or breaks down [[thiamine]] into pyrimidine and thiazole. It is an [[antinutrient]] when consumed.

The old name was "aneurinase".<ref>{{cite journal | vauthors = Fujita A, Nose Y, Kozuka S, Tashiro T, Ueda K, Sakamoto S | title = Studies on thiaminase. I. Activation of thiamine breakdown by organic bases | journal = The Journal of Biological Chemistry | volume = 196 | issue = 1 | pages = 289–95 | date = May 1952 | doi = 10.1016/S0021-9258(18)55732-X | pmid = 12980969 | doi-access = free }}</ref>

There are two types with different [[Enzyme Commission number]]s:<ref name="cornell">[https://www.ansci.cornell.edu/plants/toxicagents/thiaminase.html Thiaminases<!-- Bot generated title -->]</ref>
* Thiamine pyridinylase, Thiaminase I ({{EC number|2.5.1.2}}, {{InterPro|IPR030901}})
** pyridine + thiamine <=> 5-(2-hydroxyethyl)-4-methylthiazole + heteropyrithiamine<ref>{{cite web |title=ENZYME - 2.5.1.2 thiamine pyridinylase |url=https://enzyme.expasy.org/EC/2.5.1.2 |website=enzyme.expasy.org}}</ref>
** Secreted by ''Paenibacillus thiaminolyticus'',<ref>{{cite web |title=UniProt P45741 |url=https://www.uniprot.org/uniprotkb/P45741/entry |website=www.uniprot.org}}</ref> an anaerobic organism that occurs in the human small intestine
* Aminopyrimidine aminohydrolase, Thinaminase II ({{EC number|3.5.99.2}}, {{InterPro|1=IPR027574}}, {{InterPro|l=n|1=IPR004305}})
** 4-amino-5-aminomethyl-2-methylpyrimidine + H<sub>2</sub>O <=> 4-amino-5-hydroxymethyl-2-methylpyrimidine + NH<sub>2</sub><sup>+</sup><ref name=expasy_ii/>
** H<sub>2</sub>O + thiamine <=> 4-amino-5-hydroxymethyl-2-methylpyrimidine + 5-(2-hydroxyethyl)-4-methylthiazole + H<sup>+</sup><ref name=expasy_ii/>
** Produced by a wide range of plants and bacteria. In these organisms, it is mainly responsible for ''salvage'' of thiamine pyrimidine from degradation products, rather than the breakdown of thiamine.<ref name=expasy_ii>{{cite web |title=ENZYME - 3.5.99.2 aminopyrimidine aminohydrolase |url=https://enzyme.expasy.org/EC/3.5.99.2 |website=enzyme.expasy.org}}</ref> In bacteria, it stays inside their cells.<ref name=aneurinolyticus/>

== Structure and function ==

=== Thiaminase I ===
Thiaminase I works to cleave the pyrimidine ring in thiamin from the thiazolium ring at the methylene bridge. From there it adds a base compound to the pyrimidine, creating an analogue inhibitor of thiamin. Thiaminase I has the ability to use a multitude of C-N cleaving nucleophilic substrates like cysteine, pyridine, aniline, veratrylamine, dithiothreitol, and quinoline.<ref name=cbot/>

When analyzing the structure of Thiaminase I it shows a fold similar to that of group II periplasmic binding proteins like maltose-binding protein.<ref name=":2">{{Cite journal |last1=Jurgenson |first1=Christopher T. |last2=Begley |first2=Tadhg P. |last3=Ealick |first3=Steven E. |date=2009 |title=The Structural and Biochemical Foundations of Thiamin Biosynthesis |journal=Annual Review of Biochemistry |volume=78 |pages=569–603 |doi=10.1146/annurev.biochem.78.072407.102340 |pmc=6078420 |pmid=19348578 }}</ref> These periplasmic binding proteins have two domains that each contain an α/β fold. These two domains come together to form a deep cleft that are connected by three crossover segments. Due to this structure scientists proposed that Thiaminase I could have evolved from prehistoric periplasmic binding protein that had been responsible for up taking thiamin.<ref name=":2" /> Between the two domains, in the cleft, sit the active site for Thiaminase I. Along the cleft there are four acidic residues and six tyrosine residues. In order for Thiamin to interact with Thiaminase I it is positioned in the active site between the pyrimidine and Asp272 by two hydrogen bonds. The Glu241 the goes on to activate the Cys113 to attack C6 of the pyrimidine. This forms a zwitterionic intermediate.<ref name=":2" /> The Glu241 causes and protonation and nucleophilic attack that results in the split of the bond between the pyrimidine and the thiazole. When observing the crystalline structure, it has two α/β-type domains separated by a large cleft. At room temperature the two molecules have a noncrystallographic twofold axis that are bridged by a sulfate ion.<ref>{{cite journal |last1=Campobasso |first1=Nino |last2=Costello |first2=Colleen A. |last3=Kinsland |first3=Cynthia |last4=Begley |first4=Tadhg P. |last5=Ealick |first5=Steven E. |title=Crystal Structure of Thiaminase-I from Bacillus t hiaminolyticus at 2.0 Å Resolution |journal=Biochemistry |date=November 1998 |volume=37 |issue=45 |pages=15981–15989 |doi=10.1021/bi981673l |pmid=9843405 }}</ref>

=== Thiaminase II ===
Thiaminase II cleaves but does not add a base compound. Thiaminase II can only use water as the [[nucleophile]].{{fact|date=August 2025}}

Thiaminase II has been found to be TenA. In order to cleave the C-N bond between the thiazole and pyrimidine Thiaminase only uses water as its nucleophile. When viewing Thiaminase II it is found to have a crystal structure that has 11 helices surrounding a deep acidic pocket.<ref name=":2" /> For each monomer present in the quaternary structure it interacts with two other monomers. There are several residues like Tyr112, Phe208, Tyr47, and Tyr163 that have some sort of contribution to the π- stacking environment surrounding the HMP ligand.<ref name=":2" /> The Glu205 side chain will form a hydrogen bond with the N1 nitrogen in the pyrimidine ring. Next the Tyr163 and the Asp44 side chain come together to form the hydrogen bonds with the N3 and N4'.<ref name=":2" /> Finally the Cys135 [[catalytic residue]] is positioned near the C2 in the pyridine ring to complete the split of thiamin into its heterocycles.<ref name=":2" />

==Sources==
This enzyme can be found in a variety of different sources. It can be found in marine organisms, plants, and bacteria. Since thiamine (vitamin B<sub>1</sub>) is a very important substance required for metabolic pathways by almost all organisms, it can be very detrimental to introduce Thiaminase to a system. Frequently an organism gains this enzyme by ingesting another organism that carries it. In most cases, prey fish will contain one of the bacteria that produces this enzyme. When that prey fish is consumed raw without treatment the bacteria will transfer to the consumer.<ref name=":3">{{Cite journal |last1=Richter |first1=Catherine A. |last2=Evans |first2=Allison N. |last3=Heppell |first3=Scott A. |last4=Zajicek |first4=James L. |last5=Tillitt |first5=Donald E. |date=2023-01-13 |title=Genetic basis of thiaminase I activity in a vertebrate, zebrafish Danio rerio |journal=Scientific Reports |language=en |volume=13 |issue=1 |pages=698 |doi=10.1038/s41598-023-27612-5 |pmid=36639393 |pmc=9839694 |bibcode=2023NatSR..13..698R }}</ref> The consumer eventually will fall ill, even die, from a [[thiamine deficiency]]. This has been seen in different lab studies. Through these studies the enzyme has been found in zebra fish as well as red cornet fish.<ref name=":3" /> Cooking thiaminase-containing foods usually inactivates the enzyme.<ref name=":3" />

Sources of thiaminase I include: 
* Plants: [[bracken]] (brake),<ref name=NcCleary>{{cite journal |vauthors=NcCleary BV, Chick BF|title=The purification and properties of a thiaminase I from Nardoo (Marsilea drummondii) |journal = [[Phytochemistry (journal)|Phytochemistry]] |volume=16 |issue= 2|pages=207–213 |year=1977|doi=10.1016/S0031-9422(00)86787-4 |quote=Thiaminase I enzymes present in the culture solutions of Bacillus thiaminolyticus [3-5] and Clostridium sporogenes [6-8] have been highly purified and detailed kinetic studies performed. But, despite the importance thiaminase I enzyme in stock poisoning by bracken fern [9], there is limited information available on the properties of this or other fern thiaminases.}}</ref> [[Marsilea|nardoo]],<ref name=NcCleary/> [[Equisetum|horsetail]].<ref>{{cite journal |id={{INIST|3778153}} |last1=Fabre |first1=B |last2=Geay |first2=B. |last3=Beaufils |first3=P. |title=Thiaminase activity in ''equisetum arvense'' and its extracts |journal=Plantes médicinales et phytothérapie |date=1993 |volume=26 |issue=3 |pages=190–197 }}</ref>
* [[Fish as food|Fish]] including zebra fish,<ref name=":3"/> [[carp]] and [[goldfish]].<ref>{{cite journal | vauthors = Boś M, Kozik A | title = Some molecular and enzymatic properties of a homogeneous preparation of thiaminase I purified from carp liver | journal = Journal of Protein Chemistry | volume = 19 | issue = 2 | pages = 75–84 | date = February 2000 | pmid = 10945431 | doi = 10.1023/A:1007043530616 }}</ref>
* Bacteria such as ''[[Paenibacillus thiaminolyticus]]'' (formerly in ''Bacillus''),<ref>{{cite journal | vauthors = Wittliff JL, Airth RL | title = The extracellular thiaminase I of Bacillus thiaminolyticus. I. Purification and physicochemical properties | journal = Biochemistry | volume = 7 | issue = 2 | pages = 736–44 | date = February 1968 | pmid = 4966932 | doi = 10.1021/bi00842a032 }}</ref> ''[[Clostridium sporogenes]]'',<ref name=NcCleary/> ''[[C. botulinum]]''.<ref name=cbot>{{cite journal |last1=Sikowitz |first1=MD |last2=Shome |first2=B |last3=Zhang |first3=Y |last4=Begley |first4=TP |last5=Ealick |first5=SE |title=Structure of a Clostridium botulinum C143S thiaminase I/thiamin complex reveals active site architecture . |journal=Biochemistry |date=5 November 2013 |volume=52 |issue=44 |pages=7830–9 |doi=10.1021/bi400841g |pmid=24079939 |pmc=3883099 }}</ref>
* An African silk worm, ''[[Anaphe venata]]''; this enzyme is more heat-tolerant than other thiaminases and requires a longer cooking time<ref>{{cite journal |vauthors=Nishimune T, Watanabe Y, Okazaki H, Akai H |title=Thiamin is decomposed due to Anaphe spp. entomophagy in seasonal ataxia patients in Nigeria |journal=J. Nutr. |volume=130 |pages=1625–28 |year=2000 |issue=6 |doi=10.1093/jn/130.6.1625 |pmid=10827220 |quote=The thiaminase in the buffer extract of Anaphe pupae was type I|doi-access=free }}</ref>

Sources of thiaminase II include: 
*  ''[[Bacillus aneurinolyticus]]''<ref name=aneurinolyticus>{{cite journal |last1=中塚 |first1=敏之 |last2=鈴木 |first2=喜六 |last3=中野 |first3=長久 |last4=北岡 |first4=正三郎 |title=Bacillus aneurinolyticusの菌体内Thiaminase IIのタンパク化学的性質 |trans-title=Physiochemical Properties of Intracellular Thiaminase II of ''Bacillus aneurinolyticus'' |language=ja |journal=ビタミン |date=1988 |volume=62 |doi=10.20632/vso.62.1_15 |doi-access=free }}</ref> and ''[[Bacillus subtilis]]''.<ref>{{cite journal | vauthors = Toms AV, Haas AL, Park JH, Begley TP, Ealick SE | title = Structural characterization of the regulatory proteins TenA and TenI from Bacillus subtilis and identification of TenA as a thiaminase II | journal = Biochemistry | volume = 44 | issue = 7 | pages = 2319–29 | date = February 2005 | pmid = 15709744 | doi = 10.1021/bi0478648 }}</ref>

==Effects==

=== Function ===
It is still unclear what thiaminase does for fish, bacterial cell or insects that contain it. In ferns, thiaminase I is thought to offer protection from insects<ref>{{cite book | vauthors = Vetter J |chapter=Toxicological and Medicinal Aspects of the Most Frequent Fern Species, Pteridium aquilinum (L.) Kuhn |title=Working with Ferns: Issues and Applications|pages=361–375 |year=2010 |doi= 10.1007/978-1-4419-7162-3_25|isbn=978-1-4419-7161-6 }}</ref>

Studies have shown that thiamine hydrolase (thiaminase II), which was originally thought to be involved solely in the degradation of thiamine, has actually been identified as having a role in thiamine degradation with the salvage of the pyrimidine moiety. Thiamin hydrolysis product N-formyl-4-amino-5-aminomethyl-2-methylpyrimidine is transported into the cell and deformylated by the amidohydrolase ''ylmB'' and hydrolyzed to 5-aminoimidazole ribotide.<ref>{{cite journal | vauthors = Jenkins AH, Schyns G, Potot S, Sun G, Begley TP | title = A new thiamin salvage pathway | journal = Nature Chemical Biology | volume = 3 | issue = 8 | pages = 492–7 | date = August 2007 | pmid = 17618314 | doi = 10.1038/nchembio.2007.13 }}</ref>

=== When ingested ===
It was described in 1941 as the cause of highly mortal [[ataxic]] [[neuropathy]] in farmed [[fox]]es fed with raw [[common carp|carp]].<ref name="Green et al 1941" />

It is also known as the cause of cerebrocortical necrosis of [[cattle]] and [[polioencephalomalasia]] of [[sheep]] eating thiaminase containing plants.<ref>{{cite journal | vauthors = Ramos JJ, Marca C, Loste A, García de Jalón JA, Fernández A, Cubel T | title = Biochemical changes in apparently normal sheep from flocks affected by polioencephalomalacia | journal = Veterinary Research Communications | volume = 27 | issue = 2 | pages = 111–24 | date = February 2003 | pmid = 12718505 | doi = 10.1023/A:1022807119539 }}</ref><ref>{{cite book |last1=Evans |first1=W. Charles |title=Thiaminases and Their Effects on Animals |series=Vitamins & Hormones |date=1976 |volume=33 |pages=467–504 |doi=10.1016/S0083-6729(08)60970-X |pmid=779253 |isbn=978-0-12-709833-3 }}</ref>

It was once causing economical losses in raising [[fisheries]], e.g. in [[Yellowtail (fish)|yellowtail]] fed raw [[anchovy]] as a sole feed for a certain period, and also in [[sea bream]] and [[rainbow trout]]. The same problem is being studied in a natural food chain system.<ref>{{cite journal | vauthors = Fisher JP, Brown SB, Wooster GW, Bowser PR | title = Maternal blood, egg and larval thiamin levels correlate with larval survival in landlocked Atlantic salmon | journal = The Journal of Nutrition | volume = 128 | issue = 12 | pages = 2456–66 | date = December 1998 | pmid = 9868194 | doi = 10.1093/jn/128.12.2456 | doi-access = free }}</ref>

The larvae of a [[wild silk]] worm ''[[Anaphe venata]]'' are being consumed in a [[rain forest]] district of [[Nigeria]] as a supplemental protein nutrition, and the heat-resistant thiaminase in it is causing an acute seasonal [[ataxia|cerebellar ataxia]] named [[African seasonal ataxia]] or [[Nigerian seasonal ataxia]].<ref>{{cite journal | vauthors = Adamolekun B, Adamolekun WE, Sonibare AD, Sofowora G | title = A double-blind, placebo-controlled study of the efficacy of thiamine hydrochloride in a seasonal ataxia in Nigerians | journal = Neurology | volume = 44 | issue = 3 Pt 1 | pages = 549–51 | date = March 1994 | pmid = 8145931 | doi = 10.1212/wnl.44.3_part_1.549 }}</ref>

In 1860–61, [[Burke and Wills]] were the first Europeans to cross [[Australia]] south to north; on their return they subsisted primarily on raw [[nardoo]]-fern. It is possible that this led to their death due to the extremely high levels of thiaminase contained in nardoo. The Aborigines prepared nardoo by soaking the sporocarps in water for at least a day to avoid the effects of [[thiamine deficiency]] that would result from ingesting the leaves raw.  In the explorers' journals they noted many symptoms of thiamine deficiency, so it is thought that they did not soak the nardoo long enough.  Eventually thiamine deficiency could have led to their demise.<ref name="cornell" />  It is noteworthy to mention that there are several other hypotheses regarding what may have killed Burke and Wills and it is widely disagreed upon by historians and scientists alike.{{Citation needed|date=August 2024}}

== References ==
{{Reflist|30em|refs=

<ref name = "Green et al 1941">{{cite journal | vauthors=Green RG, Carlson WE, Evans CA | title=A deficiency disease of foxes produced by feeding fish | journal=The Journal of Nutrition | volume=21 | issue=3 | pages=243–256 | date=1941 | doi=10.1093/jn/21.3.243}}</ref>

}}

== External links ==
* {{MeshName|thiaminase+I}} 
* {{MeshName|thiaminase+II}} 

{{Carbon-nitrogen non-peptide hydrolases}}
{{Alkyl and aryl transferases}}
{{Enzymes}}
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[[Category:EC 2.5.1]]
[[Category:Antinutrients]]