Tryptophan synthase (EC:220.127.116.11) catalyzes the last step in the biosynthesis of tryptophan [PMID: 2679363, PMID: 1366510]:
L-serine + 1-(indol-3-yl)glycerol 3-phosphate = L-tryptophan + glyceraldehyde 3-phosphate + H2O
It has two functional domains, each found in bacteria and plants on a separate subunit. In Escherichia coli, the two subunits, A and B, are encoded by the trpA and trpB genes respectively. The alpha chain is for the aldol cleavage of indoleglycerol phosphate to indole and glyceraldehyde 3-phosphate and the beta chain IPR006653 is for the synthesis of tryptophan from indole and serine. In fungi the two domains are fused together in a single multifunctional protein, in the order: (NH2-A-B-COOH) [PMID: 2521855, PMID: 2734310]. The two domains of the Neurospora crassa polypeptide are linked by a connector of 54-amino acid residues that has less than 25% identity to the 45-residue connector of the Saccharomyces cerevisiae (Baker's yeast) polypeptide. Two acidic residues are believed to serve as proton donors/acceptors in the enzyme's catalytic mechanism.
GO:0006568 tryptophan metabolic process
GO:0004834 tryptophan synthase activity
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