期刊
BIOCHEMISTRY
卷 55, 期 51, 页码 7043-7046出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.biochem.6b01127
关键词
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资金
- Gordon and Betty Moore Foundation
- Beckman Institute
- Sanofi-Aventis Bioengineering Research Program at Caltech
- Ruth Kirschstein National Institutes of Health Postdoctoral Fellowship [F32G110851]
- Alfonso Martin Escudero Foundation
Tryptophan synthase (TrpS) catalyzes the final steps in the biosynthesis of L-tryptophan from L-serine (Ser) and indole-3-glycerol phosphate (IGP). We report that native TrpS can also catalyze a productive reaction with L-threonine (Thr), leading to (2S,3S)-beta-methyltryptophan. Surprisingly, beta-substitution occurs in vitro with a 3.4-fold higher catalytic efficiency for Ser over Thr using saturating indole, despite a >82000-fold preference for Ser in direct competition using IGP. Structural data identify a novel product binding site, and kinetic experiments clarify the atypical mechanism of specificity: Thr binds efficiently but decreases the affinity for indole and disrupts the allosteric signaling that regulates the catalytic cycle.
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