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The gene yfdU from Escherichia coli encodes a putative oxalyl coenzyme A decarboxylase, a thiamine diphosphate-dependent enzyme that is potentially involved in the degradation of oxalate. The enzyme has been purified to homogeneity. The kinetic constants for conversion of the substrate oxalyl coenzyme A by the enzyme in the absence and presence of the inhibitor coenzyme A, as well as in the absence and presence of the activator adenosine 5′-diphosphate, were determined using a novel continuous optical assay. The effects of these ligands on the solution and crystal structure of the enzyme were studied using small-angle X-ray scattering and X-ray crystal diffraction. Analyses of the obtained crystal structures of the enzyme in complex with the cofactor thiamine diphosphate, the activator adenosine 5′-diphosphate and the inhibitor acetyl coenzyme A, as well as the corresponding solution scattering patterns, allow comparison of the oligomer structures of the enzyme complexes under various experimental conditions, and provide insights into the architecture of substrate and effector binding sites. Structured digital abstract • : EcODC (uniprotkb: ) and EcODC (uniprotkb: ) bind ( ) by X-ray scattering ( ) • : EcODC (uniprotkb: ) and EcODC (uniprotkb: ) bind ( ) by X-ray crystallography ( ) [ABSTRACT FROM AUTHOR]

Abstract: The allosteric substrate activation of pyruvate decarboxylases was studied for more than 30 years using varying techniques and ending up in different hypotheses on the molecular mechanism of substrate activation of this enzyme. Now, a number of high-resolution structures of the pyruvate decarboxylase species from Saccharomyces cerevisiae and from Kluyveromyces lactis – both wild type and variants in complex with covalently bound substrate or substrate surrogates – provided for the first time structural insights to decipher the mechanism of allosteric activation by describing the signal transduction pathway from the regulatory to the active site in detail. Here, the mechanistic studies on substrate activation of pyruvate decarboxylases are reviewed from a historical point of view, demonstrating that important parts of the different hypotheses got carried away with our new mechanism drawn from latest results of experiments on activation kinetics, small-angle X-ray solution scattering and X-ray crystal diffraction. [Copyright &y& Elsevier]

The crystal structure of pyruvate decarboxylase from Kluyveromyces lactis has been determined to 2.26 Å resolution. Like other yeast enzymes, Kluyveromyces lactis pyruvate decarboxylase is subject to allosteric substrate activation. Binding of substrate at a regulatory site induces catalytic activity. This process is accompanied by conformational changes and subunit rearrangements. In the nonactivated form of the corresponding enzyme from Saccharomyces cerevisiae, all active sites are solvent accessible due to the high flexibility of loop regions 106–113 and 292–301. The binding of the activator pyruvamide arrests these loops. Consequently, two of four active sites become closed. In Kluyveromyces lactis pyruvate decarboxylase, this half-side closed tetramer is present even without any activator. However, one of the loops (residues 105–113), which are flexible in nonactivated Saccharomyces cerevisiae pyruvate decarboxylase, remains flexible. Even though the tetramer assemblies of both enzyme species are different in the absence of activating agents, their substrate activation kinetics are similar. This implies an equilibrium between the open and the half-side closed state of yeast pyruvate decarboxylase tetramers. The completely open enzyme state is favoured for Saccharomyces cerevisiae pyruvate decarboxylase, whereas the half-side closed form is predominant for Kluyveromyces lactis pyruvate decarboxylase. Consequently, the structuring of the flexible loop region 105–113 seems to be the crucial step during the substrate activation process of Kluyveromyces lactis pyruvate decarboxylase. [ABSTRACT FROM AUTHOR]

Enterobacter cloacae , isolated from the rhizosphere of cucumbers, produces large amounts of indole-3-acetic acid. Indolepyruvate decarboxylase, the key enzyme in the biosynthetic pathway of indole-3-acetic acid, catalyses the formation of indole-3-acetaldehyde and carbon dioxide from indole-3-pyruvic acid. The enzyme requires the cofactors thiamine diphosphate and magnesium ions for catalytic activity. Recombinant indolepyruvate decarboxylase was purified from the host Escherichia coli strain JM109. Specificity of the enzyme for the substrates indole-3-pyruvic acid, pyruvic acid, benzoylformic acid, and seven benzoylformic acid analogues was investigated using a continuous optical assay. Stopped-flow kinetic data showed no indication for substrate activation in the decarboxylation reaction of indole-3-pyruvic acid, pyruvic acid or benzoylformic acid. Size exclusion chromatography and small angle X-ray solution scattering experiments suggested the tetramer as the catalytically active state and a pH-dependent subunit association equilibrium. Analysis of the kinetic constants of the benzoylformic acid analogues according to Hansch et al . [Hansch, C., Leo, A., Unger, S.H., Kim, K.H., Nikaitani, D & Lien, E.J. (1973) J. Med. Chem. 16, 1207–1216] and comparison with indole-3-pyruvic acid conversion by pyruvate decarboxylases from Saccharomyces cerevisiae and Zymomonas mobilis provided some insight into the catalytic mechanism of indolepyruvate decarboxylase. [ABSTRACT FROM AUTHOR]

Pyruvate decarboxylase (EC 4.1.1.1) was isolated and purified from the yeast Kluyveromyces lactis . The properties of this enzyme relating to the native oligomeric state, the subunit size, the nucleotide sequence of the coding gene(s), the catalytic activity, and protein fluorescence as well as circular dichroism are very similar to those of the well characterized pyruvate decarboxylase species from yeast. Remarkable differences were found in the substrate activation behaviour of the two pyruvate decarboxylases using three independent methods: steady-state kinetics, stopped-flow measurements, and kinetic dilution experiments. The dependence of the observed activation rate constant on the substrate concentration of pyruvate decarboxylase from K. lactis showed a minimum at a pyruvate concentration of 1.5 mm. According to the mechanism of substrate activation suggested this local minimum occurs due to the big ratio of the dissociation constants for the binding of the first (regulatory) and the second (catalytic) substrate molecule. The microscopic rate constants of the substrate activation could be determined by a refined fit procedure. The influence of the artificial activator pyruvamide on the activation of the enzyme was studied. [ABSTRACT FROM AUTHOR]