Pyrimidine (PYR) binding domain of POX and related proteins.
Thiamine pyrophosphate (TPP family), pyrimidine (PYR) binding domain of pyruvate oxidase (POX) and related protiens subfamily. The PYR domain is found in many key metabolic enzymes which use TPP (also known as thiamine diphosphate) as a cofactor. TPP binds in the cleft formed by a PYR domain and a PP domain. The PYR domain, binds the aminopyrimidine ring of TPP, the PP domain binds the diphosphate residue. A polar interaction between the conserved glutamate of the PYR domain and the N1' of the TPP aminopyrimidine ring is shared by most TPP-dependent enzymes, and participates in the activation of TPP. For glyoxylate carboligase, which belongs to this subfamily, but lacks this conserved glutamate, the rate of the initial TPP activation step is reduced but the ensuing steps of the enzymic reaction proceed efficiently. The PYR and PP domains have a common fold, but do not share strong sequence conservation. The PP domain is not included in this sub-family. Most TPP-dependent enzymes have the PYR and PP domains on the same subunit although these domains can be alternatively arranged in the primary structure. TPP-dependent enzymes are multisubunit proteins, the smallest catalytic unit being a dimer-of-active sites, for many the active sites lie between PP and PYR domains on different subunits. POX decarboxylates pyruvate, producing hydrogen peroxide and the energy-storage metabolite acetylphosphate. This subfamily includes pyruvate decarboxylase (PDC) and indolepyruvate decarboxylase (IPDC). PDC catalyzes the conversion of pyruvate to acetaldehyde and CO2 in alcoholic fermentation. IPDC plays a role in the indole-3-pyruvic acid (IPA) pathway in plants and various plant-associated bacteria, it catalyzes the decarboxylation of IPA to IAA. This subfamily also includes the large catalytic subunit of acetohydroxyacid synthase (AHAS). AHAS catalyzes the condensation of two molecules of pyruvate to give the acetohydroxyacid, 2-acetolactate, a precursor of the branched chain amino acids, valine and leucine. AHAS also catalyzes the condensation of pyruvate and 2-ketobutyrate to form 2-aceto-2-hydroxybutyrate in isoleucine biosynthesis. Methanococcus jannaschii sulfopyruvate decarboxylase (MjComDE) and phosphonopyruvate decarboxylase (PpyrDc) also belong to this subfamily. PpyrDc is a homotrimeric enzyme having the PP and PYR domains tandemly arranged on the same subunit. It functions in the biosynthesis of C-P compounds such as bialaphos tripeptide in Streptomyces hygroscopicus. MjComDE is a dodecamer having the PYR and PP domains on different subunits, it has six alpha (PYR/ComD) subunits and six beta (PP/ComE) subunits. MjComDE catalyzes the decarboxylation of sulfopyruvic acid to sulfoacetaldehyde in the coenzyme M pathway.
Comment:proteins in this group are either homotetramers (dimer-of-homodimers) (e.g. E. coli MenD, L. plantarum POX, K. lactis PDC, P. fluorescens BAL,), or homodimers (e.g. L. lactis KdcA, S. cerevisiae AHAS). There are two TPP-binding sites per homodimer.
Comment:each TPP binds in a site lying between a PYR domain and a PP domain from different subunits.