α-Hydroxy-β-keto acid rearrangement-decarboxylation: impact on thiamine diphosphate-dependent enzymatic transformations

• Published in: Organic & biomolecular chemistry 2013-01, Vol.11 (2), p.252-256
• Main Authors: Beigi, Maryam, Loschonsky, Sabrina, Lehwald, Patrizia, Brecht, Volker, Andrade, Susana L A, Leeper, Finian J, Hummel, Werner, Müller, Michael
• Format: Article
• Language: English
• Subjects: Biocatalysis; Decarboxylation; Escherichia coli - enzymology; Escherichia coli Proteins - metabolism; Ketoglutaric Acids - chemistry; Ketoglutaric Acids - metabolism; Pyruvate Oxidase - metabolism; Substrate Specificity; Thiamine Pyrophosphate - chemistry; Thiamine Pyrophosphate - metabolism
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c2ob26981c

The thiamine diphosphate (ThDP) dependent MenD catalyzes the reaction of α-ketoglutarate with pyruvate to selectively form 4-hydroxy-5-oxohexanoic acid 2, which seems to be inconsistent with the assumed acyl donor role of the physiological substrate α-KG. In contrast the reaction of α-ketoglutarate with acetaldehyde gives exclusively the expected 5-hydroxy-4-oxo regioisomer 1. These reactions were studied by NMR and CD spectroscopy, which revealed that with pyruvate the observed regioselectivity is due to the rearrangement-decarboxylation of the initially formed α-hydroxy-β-keto acid rather than a donor-acceptor substrate role variation. Further experiments with other ThDP-dependent enzymes, YerE, SucA, and CDH, verified that this degenerate decarboxylation can be linked to the reduced enantioselectivity of acyloins often observed in ThDP-dependent enzymatic transformations.