Structure and mechanistic implications of a tryptophan synthase quinonoid intermediate

Way station. Quinonoid intermediates play a key role in the catalytic mechanism of pyridoxal 5′-phosphate (PLP)-dependent enzymes. Whereas structures of other PLP-bound reaction intermediates have been determined, a high-quality structure of a quinonoid species has not been reported. We present the crystal structure of the indoline quinonoid intermediate of tryptophan synthase (see figure) and discuss its implications for the enzymatic mechanism and allosteric regulation