Therefore, bacterial PDCs and their hosts have been the focus of extensive characterization and engineering efforts to develop ethanologenic strains ,. ventriculi), the PDC forms part of the fermentative pathway leading to ethanol production. In higher organisms and most prokaryotes ( Z. Several of the plant and yeast PDCs have been isolated and characterized, however by contrast only five bacterial PDCs have been described, namely those from Zymomonas mobilis (ZmPDC), Zymobacter palmae (ZpPDC), Sarcina ventriculi (SvPDC), Acetobacter pasteurianus (ApPDC) and Gluconobacter oxydans (GoPDC). Although widespread in the plant kingdom and amongst ascomycetous yeasts and fungi, PDCs are comparatively rare in prokaryotes. A recent study proposed a PDC capable of co-factor independent decarboxylation of pyruvate, however this discovery has been refuted. All characterized PDCs are dependent on the cofactors thiamine diphosphate (ThDP) and Mg 2+. Pyruvate decarboxylase (PDC, EC 4.1.1.1) is the enzyme responsible for the non-oxidative decarboxylation of pyruvate to acetaldehyde and carbon dioxide. The lack of activity on indole-3-pyruvate excludes this decarboxylase as the enzyme responsible for indole acetic acid production in G. The pH optimum together with reduced thermostability likely reflect the host organisms niche and conditions under which these properties have been naturally selected for. pasteurianus and suggests strong selective pressure to keep the enzyme characteristics in a narrow range. The crystal structure of GdPDC indicates the enzyme to be evolutionarily closely related to homologues from Z. diazotrophicus (PAL5) and lays the groundwork for future research into its role in this endosymbiont. This is the first study of the PDC from G. Structural differences occur in two loci, involving the regions Thr341 to Thr352 and Asn499 to Asp503. Indole-3-pyruvate does not serve as a substrate for the enzyme. pasteurianus PDC (ApPDC) with a rmsd value of 0.57 Å for Cα when comparing GdPDC to that of ApPDC. The structure is highly similar to those described for Z. The enzyme is not thermostable (T ½ of 18 minutes at 60☌) and the calculated number of bonds between monomers and dimers do not give clear indications for the relatively lower thermostability compared to other PDCs.
s −1 at pH 5), pH opt of 5.5 and T opt at 45☌.Enzyme kinetic analysis indicates a high affinity for pyruvate ( K M 0.06 mM at pH 5), high catalytic efficiencies (1.3 This study reports the kinetic characterization and the crystal structure of a PDC from Gluconacetobacter diazotrophicus (GdPDC). All of these organisms are of commercial importance. diazotrophicus (GdPDC) and Acetobacter pasteutrianus (ApPDC). Examples include Gluconobacter oxydans (GoPDC), G. PDCs from the Acetobacteraceae and their role in metabolism have not been characterized to the same extent. PDCs from Zymomonas mobilis (ZmPDC), Zymobacter palmae (ZpPDC) and Sarcina ventriculi (SvPDC) have been characterized and ZmPDC has been produced successfully in a range of heterologous hosts. Their role in ethanol production and in bacterially mediated ethanologenic processes has, however, ensured a continued and growing interest. Bacterial pyruvate decarboxylases (PDC) are rare.
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