Also catalyzes the conversion of serine and indole into tryptophan and water and of indoleglycerol phosphate into indole and glyceraldehyde phosphate.

In some organisms, this enzyme is part of a multifunctional protein together with one or more components of the system for biosynthesis of tryptophan.

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, each domain is found on a separate subunit (a and b chains), while in fungi the two domains are fused together on a single multifunctional protein.

As a signature pattern for the a chain, it has been 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.
Reference

The b chain of the enzyme 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. The signature pattern for the tryptophan synthase beta chain is derived from that conserved region.
Reference