Millisecond Timescale Motions Connect Amino Acid Interaction Networks in Alpha Tryptophan Synthase.

ABSTRACT: Tryptophan synthase is a model system for understanding allosteric regulation within enzyme complexes. Amino acid interaction networks were previously delineated in the isolated alpha subunit (?TS) in the absence of the beta subunit (?TS). The amino acid interaction networks were different between the ligand-free enzyme and the enzyme actively catalyzing turnover. Previous X-ray crystallography studies indicated only minor localized changes when ligands bind ?TS, and so, structural changes alone could not explain the changes to the amino acid interaction networks. We hypothesized that the network changes could instead be related to changes in conformational dynamics. As such, we conducted nuclear magnetic resonance relaxation studies on different substrate- and products-bound complexes of ?TS. Specifically, we collected 15N R2 relaxation dispersion data that reports on microsecond-to-millisecond timescale motion of backbone amide groups. These experiments indicated that there are conformational exchange events throughout ?TS. Substrate and product binding change specific motional pathways throughout the enzyme, and these pathways connect the previously identified network residues. These pathways reach the ?TS/?TS binding interface, suggesting that the identified dynamic networks may also be important for communication with the ?TS subunit.

SUBMITTER: O'Rourke KF 

PROVIDER: S-EPMC6236060 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature