==Roles of His291-alpha and His146-beta' in the reductive acylation reaction catalyzed by human branched-chain alpha-ketoacid dehydrogenase==

<StructureSection load='1ols' size='340' side='right'caption='[[1ols]], [[Resolution|resolution]] 1.85&Aring;' scene=''>

<table><tr><td colspan='2'>[[1ols]] is a 2 chain structure with sequence from [http://en.wikipedia.org/wiki/Human Human]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1OLS OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1OLS FirstGlance]. <br>

</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat"><scene name='pdbligand=GOL:GLYCEROL'>GOL</scene>, <scene name='pdbligand=K:POTASSIUM+ION'>K</scene>, <scene name='pdbligand=MN:MANGANESE+(II)+ION'>MN</scene>, <scene name='pdbligand=TDP:THIAMIN+DIPHOSPHATE'>TDP</scene></td></tr>

<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1ols FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1ols OCA], [http://pdbe.org/1ols PDBe], [http://www.rcsb.org/pdb/explore.do?structureId=1ols RCSB], [http://www.ebi.ac.uk/pdbsum/1ols PDBsum], [http://prosat.h-its.org/prosat/prosatexe?pdbcode=1ols ProSAT]</span></td></tr>

== Disease ==

[[http://www.uniprot.org/uniprot/ODBA_HUMAN ODBA_HUMAN]] Defects in BCKDHA are a cause of maple syrup urine disease type IA (MSUD1A) [MIM:[http://omim.org/entry/248600 248600]]. MSUD is an autosomal recessive disorder characterized by mental and physical retardation, feeding problems, and a maple syrup odor to the urine.<ref>PMID:2060625</ref> <ref>PMID:8037208</ref> <ref>PMID:2703538</ref> <ref>PMID:2241958</ref> <ref>PMID:1867199</ref> <ref>PMID:1885764</ref> <ref>PMID:8161368</ref> <ref>PMID:7883996</ref> [[http://www.uniprot.org/uniprot/ODBB_HUMAN ODBB_HUMAN]] Defects in BCKDHB are the cause of maple syrup urine disease type IB (MSUD1B) [MIM:[http://omim.org/entry/248600 248600]]. MSUD is an autosomal recessive disorder characterized by mental and physical retardation, feeding problems, and a maple syrup odor to the urine.<ref>PMID:8161368</ref> <ref>PMID:11509994</ref> <ref>PMID:22326532</ref>

== Function ==

[[http://www.uniprot.org/uniprot/ODBA_HUMAN ODBA_HUMAN]] The branched-chain alpha-keto dehydrogenase complex catalyzes the overall conversion of alpha-keto acids to acyl-CoA and CO(2). It contains multiple copies of three enzymatic components: branched-chain alpha-keto acid decarboxylase (E1), lipoamide acyltransferase (E2) and lipoamide dehydrogenase (E3). [[http://www.uniprot.org/uniprot/ODBB_HUMAN ODBB_HUMAN]] The branched-chain alpha-keto dehydrogenase complex catalyzes the overall conversion of alpha-keto acids to acyl-CoA and CO(2). It contains multiple copies of three enzymatic components: branched-chain alpha-keto acid decarboxylase (E1), lipoamide acyltransferase (E2) and lipoamide dehydrogenase (E3).

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== Publication Abstract from PubMed ==

We report here that alterations of either His291-alpha or His146-beta' in the active site of human branched-chain alpha-ketoacid dehydrogenase (E1b) impede both the decarboxylation and the reductive acylation reactions catalyzed by E1b as well as the binding of cofactor thiamin diphosphate (ThDP). In a refined human E1b active-site structure, His291-alpha, which aligns with His407 in Escherichia coli pyruvate dehydrogenase and His263 in yeast transketolase, is on a largely ordered phosphorylation loop. The imidazole ring of His291-alpha in E1b coordinates to the terminal phosphate oxygen atoms of bound ThDP. The N3 atom of wild-type His146-beta', which can be protonated, binds a water molecule and points toward the aminopyrimidine ring of ThDP. Remarkably, the H291A-alpha mutation results in a complete order-to-disorder transition of the loop region, which precludes the binding of the substrate lipoyl-bearing domain to E1b. The H146A-beta' mutation, on the other hand, does not alter the loop structure, but nullifies the reductive acylation activity of E1b. Our results suggest that: 1) His291-alpha plays a structural rather than a catalytic role in the binding of cofactor ThDP and the lipoyl-bearing domain to E1b, and 2) His146-beta' is an essential catalytic residue, probably functioning as a proton donor in the reductive acylation of lipoamide on the lipoyl-bearing domain.

Roles of His291-alpha and His146-beta' in the reductive acylation reaction catalyzed by human branched-chain alpha-ketoacid dehydrogenase: refined phosphorylation loop structure in the active site.,Wynn RM, Machius M, Chuang JL, Li J, Tomchick DR, Chuang DT J Biol Chem. 2003 Oct 31;278(44):43402-10. Epub 2003 Aug 5. PMID:12902323<ref>PMID:12902323</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>

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<div class="pdbe-citations 1ols" style="background-color:#fffaf0;"></div>

==See Also==

*[[2-oxoisovalerate dehydrogenase 3D structures|2-oxoisovalerate dehydrogenase 3D structures]]

== References ==

<references/>

[[Category: Human]]

[[Category: Chuang, D T]]

[[Category: Branched-chain]]

[[Category: Thiamine phosphate]]