InterPro domain: IPR023026

Tryptophan synthase catalyses 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: alpha chain ( IPR002028 ) is for the aldol cleavage of indoleglycerol phosphate to indole and glyceraldehyde 3-phosphate and beta chain is for the synthesis of tryptophan from indole and serine. In fungi the two domains are fused together on a single multifunctional protein [ 3 ].

The beta chain of the enzyme, represented here, requires pyridoxal-phosphate as a cofactor. The pyridoxal-phosphate group is attached to a lysine residue. The region around this lysine residue also contains two histidine residues which are part of the pyridoxal-phosphate binding site.

This entry also contains sequences that represent a family of pyridoxal-phosphate dependent enzymes that are closely related to the beta subunit of tryptophan synthase. However, the only case in which a member of this family replaces a member of TIGR00263 is in Sulfolobus species which contain two sequences which hit this model, one of which is proximal to the alpha subunit. In every other case so far, either the species appears not to make tryptophan (there is no trp synthase alpha subunit), or a trp synthase beta subunit matching TIGR00263 is also found.

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. A gene encoding the tryptophan synthase beta subunit of Arabidopsis thaliana. Proc. Natl. Acad. Sci. U.S.A. 86, 4604-8