Protein architecture, dynamics and allostery in tryptophan synthase channeling.

The alpha 2 beta 2 form of the tryptophan synthase bienzyme complex catalyses the last two steps in the synthesis of L-tryptophan, consecutive processes that depend on the channeling of the common metabolite, indole, between the sites of the alpha- and beta-subunits through a 25 A-long tunnel. The channeling of indole and the coupling of the activities of the two sites are controlled by allosteric signals derived from covalent transformations at the beta-site that switch the enzyme between an open, low-activity state, to which ligands bind, and a closed, high-activity state, which prevents the escape of indole.