Allosteric Communication in the Tryptophan Synthase Bienzyme Complex: Roles

In the tryptophan synthase 22 bienzyme complex, indole, generated by the cleavage of IGP,1 is directly transferred from the -site to the -site via a 25 Å long interconnecting tunnel. To ensure the efficiency of indole channeling, site-site communication in this system functions both to coordinate the catalytic activities of the - and -sites (Scheme 1), and to prevent the escape of indole. The allosteric transitions among conformation states play two important functions in the regulation of substrate channeling in tryptophan synthase: (a) open subunit conformation states that accommodate substrate binding and release are switched to closed conformation states that activate the sites, and (b) the conversion of the -dimeric units to the closed conformation state prevents the escape of indole.

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