InterPro domain: IPR002028

Tryptophan synthase ( 4.2.1.20 ) catalyzes the last step in the biosynthesis of tryptophan [ 1 , 2 ]: L-serine + 1-(indol-3-yl)glycerol 3-phosphate = L-tryptophan + glyceraldehyde 3-phosphate + H ₂ O 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) [ 3 , 4 ]. 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.

1. Evolution of a biosynthetic pathway: the tryptophan paradigm. Annu. Rev. Microbiol. 43, 567-600
2. The tryptophan synthase multienzyme complex: exploring structure-function relationships with X-ray crystallography and mutagenesis. Biotechnology (N.Y.) 8, 27-32
3. Nucleotide sequence of the Neurospora crassa trp-3 gene encoding tryptophan synthetase and comparison of the trp-3 polypeptide with its homologs in Saccharomyces cerevisiae and Escherichia coli. J. Biol. Chem. 264, 3840-8
4. A gene encoding the tryptophan synthase beta subunit of Arabidopsis thaliana. Proc. Natl. Acad. Sci. U.S.A. 86, 4604-8