1qpb
PYRUVATE DECARBOYXLASE FROM YEAST (FORM B) COMPLEXED WITH PYRUVAMIDE
Structural highlights
FunctionPDC1_YEAST Major of three pyruvate decarboxylases (PDC1, PDC5, PDC6) implicated in the nonoxidative conversion of pyruvate to acetaldehyde and carbon dioxide during alcoholic fermentation. Most of the produced acetaldehyde is subsequently reduced to ethanol, but some is required for cytosolic acetyl-CoA production for biosynthetic pathways. The enzyme is also one of five 2-oxo acid decarboxylases (PDC1, PDC5, PDC6, ARO10, and THI3) able to decarboxylate more complex 2-oxo acids (alpha-ketoacids) than pyruvate, which seem mainly involved in amino acid catabolism. Here the enzyme catalyzes the decarboxylation of amino acids, which, in a first step, have been transaminated to the corresponding 2-oxo acids. In a third step, the resulting aldehydes are reduced to alcohols, collectively referred to as fusel oils or alcohols. Its preferred substrates are the transaminated amino acids valine, isoleucine, phenylalanine, and tryptophan, whereas leucine is no substrate. In a side-reaction the carbanionic intermediate (or active aldehyde) generated by decarboxylation or by activation of an aldehyde can react with an aldehyde via condensation (or carboligation) yielding a 2-hydroxy ketone, collectively called acyloins.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe crystal structure of the complex of the thiamine diphosphate dependent tetrameric enzyme pyruvate decarboxylase (PDC) from brewer's yeast strain with the activator pyruvamide has been determined to 2.4 A resolution. The asymmetric unit of the crystal contains two subunits, and the tetrameric molecule is generated by crystallographic symmetry. Structure analysis revealed conformational nonequivalence of the active sites. One of the two active sites in the asymmetric unit was found in an open conformation, with two active site loop regions (residues 104-113 and 290-304) disordered. In the other subunit, these loop regions are well-ordered and shield the active site from the bulk solution. In the closed enzyme subunit, one molecule of pyruvamide is bound in the active site channel, and is located in the vicinity of the thiazolium ring of the cofactor. A second pyruvamide binding site was found at the interface between the Pyr and the R domains of the subunit in the closed conformation, about 10 A away from residue C221. This second pyruvamide molecule might function in stabilizing the unique orientation of the R domain in this subunit which in turn is important for dimer-dimer interactions in the activated tetramer. No difference electron density in the close vicinity of the side chain of residue C221 was found, indicating that this residue does not form a covalent adduct with an activator molecule. Kinetic experiments showed that substrate activation was not affected by oxidation of cysteine residues and therefore does not seem to be dependent on intact thiol groups in the enzyme. The results suggest that a disorder-order transition of two active-site loop regions is a key event in the activation process triggered by the activator pyruvamide and that covalent modification of C221 is not required for this transition to occur. Based on these findings, a possible mechanism for the activation of PDC by its substrate, pyruvate, is proposed. The structural basis of substrate activation in yeast pyruvate decarboxylase. A crystallographic and kinetic study.,Lu G, Dobritzsch D, Baumann S, Schneider G, Konig S Eur J Biochem. 2000 Feb;267(3):861-8. PMID:10651824[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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