Tryptophan synthase beta chain/beta chain-like <p>Tryptophan synthase catalyzes the last step in the biosynthesisof tryptophan [<cite idref="PUB00000116"/>, <cite idref="PUB00000769"/>]:<reaction>L-serine + 1-(indol-3-yl)glycerol 3-phosphate = L-tryptophan + glyceraldehyde 3-phosphate + H₂O</reaction>It has two functional domains, each found in bacteria and plants on aseparate subunit: alpha chain (<db_xref db="INTERPRO" dbkey="IPR002028"/>) is for the aldol cleavage of indoleglycerol phosphate to indole andglyceraldehyde 3-phosphate and beta chain is for the synthesis of tryptophan fromindole and serine. In fungi the two domains are fused together on a single multifunctional protein [<cite idref="PUB00004683"/>].</p><p>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.</p><p>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.</p>