PROSITE documentation PDOC00151

Tryptophan synthase alpha chain signature

Tryptophan synthase (EC 4.2.1.20) catalyzes the last step in the biosynthesis of tryptophan: the conversion of indoleglycerol phosphate and serine, to tryptophan and glyceraldehyde 3-phosphate [1,2]. It has two functional domains: one for the aldol cleavage of indoleglycerol phosphate to indole and glyceraldehyde 3-phosphate and the other for the synthesis of tryptophan from indole and serine. In bacteria and plants [3], each domain is found on a separate subunit (α and β chains), while in fungi the two domains are fused together on a single multifunctional protein.

As a signature pattern for the α chain, we selected a conserved region that contains three conserved acidic residues. The first and the third acidic residues are believed to serve as proton donors/acceptors in the enzyme's catalytic mechanism.