TRPC

trpC is a gene commonly found in bacteria, and in some archaea and fungi, that participates in the biosynthesis of the essential amino acid tryptophan. The product of trpC can vary by organism: in many bacteria it encodes a bifunctional enzyme with both indole-3-glycerol phosphate synthase (IGPS) activity and N-(5'-phosphoribosyl)-anthranilate isomerase activity (PRA isomerase); in other species, these two activities are encoded by separate genes, with trpC typically coding for IGPS alone and PRA isomerase provided by trpF.

In organisms where trpC is bifunctional, the enzyme catalyzes two consecutive steps in the tryptophan pathway. First, PRA isomerase activity rearranges N-(5'-phosphoribosyl)anthranilate to a phosphoribosyl isomer intermediate. Second, IGPS activity catalyzes cyclization and dehydration to form indole-3-glycerol phosphate. This compound is then converted, via subsequent enzymes TrpA and TrpB (tryptophan synthase subunits), into tryptophan.

Genomic context typically places trpC within the tryptophan operon, along with other genes encoding enzymes of the pathway. Regulation often involves feedback inhibition by tryptophan, mediated by the TrpR repressor in many bacteria, adjusting operon expression in response to tryptophan levels.

Structure and evolution vary by species. IGPS domains are part of the TIM-barrel fold family, and bifunctional TrpC enzymes possess two catalytic domains in a single polypeptide. The presence or absence of separate trpF genes reflects evolutionary divergence in the organization of the tryptophan biosynthesis genes across different taxa.

See also: tryptophan biosynthesis operon.