Pyrimidine (PYR) binding domain of 1-deoxy-D-xylulose-5-phosphate synthase (DXS), transketolase (TK), and related proteins.
Thiamine pyrophosphate (TPP) family, pyrimidine (PYR) binding domain of 1-deoxy-D-xylulose-5-phosphate synthase (DXS), transketolase (TK), and the beta subunits of the E1 component of the human pyruvate dehydrogenase complex (E1- PDHc), 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. 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. Like many TPP-dependent enzymes DXS and TK are homodimers having a PYR and a PP domain on the same subunit. TK has two active sites per dimer which lie between PYR and PP domains of different subunits. For DXS each active site is located at the interface of a PYR and a PP domain from the same subunit. E1-PDHc is an alpha2beta2 dimer-of-heterodimers having two active sites but having the PYR and PP domains arranged on separate subunits, the PYR domains on the beta subunits, the PP domains on the alpha subunits. DXS is a regulatory enzyme of the mevalonate-independent pathway involved in terpenoid biosynthesis, it catalyzes a transketolase-type condensation of pyruvate with D-glyceraldehyde-3-phosphate to form 1-deoxy-D-xylulose-5-phosphate (DXP) and carbon dioxide. TK catalyzes the transfer of a two-carbon unit from ketose phosphates to aldose phosphates. In heterotrophic organisms, TK provides a link between glycolysis and the pentose phosphate pathway and provides precursors for nucleotide, aromatic amino acid and vitamin biosynthesis. TK also plays a central role in the Calvin cycle in plants. PDHc catalyzes the irreversible oxidative decarboxylation of pyruvate to produce acetyl-CoA in the bridging step between glycolysis and the citric acid cycle. This subfamily includes the beta subunits of the E1 component of the acetoin dehydrogenase complex (ADC) and the branched chain alpha-keto acid dehydrogenase/2-oxoisovalerate dehydrogenase complex (BCADC). ADC participates in the breakdown of acetoin. BCADC catalyzes the oxidative decarboxylation of 4-methyl-2-oxopentanoate, 3-methyl-2-oxopentanoate and 3-methyl-2-oxobutanoate during the breakdown of branched chain amino acids.