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Time-resolved crystallography reveals allosteric communication aligned with molecular breathing

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Science  13 Sep 2019:
Vol. 365, Issue 6458, pp. 1167-1170
DOI: 10.1126/science.aaw9904

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Active sites that move together

Enzymes often form dimers or higher-order oligomers, even when each active site is isolated and the reactions are simple. But the effect of a neighbor can be profound. Mehrabi et al. used a photolabile compound to initiate a reaction in the enzyme fluoroacetate dehalogenase, which they could follow by time-resolved serial synchrotron crystallography. Snapshots of the reaction revealed coupled allosteric motions between the two active sites of the dimeric enzyme. Each active site traded the ability to bind substrate and catalyze the reaction, such that only one was engaged at a time. This behavior is common in enzymes but is rarely visualized and still poorly understood.

Science, this issue p. 1167

Abstract

A comprehensive understanding of protein function demands correlating structure and dynamic changes. Using time-resolved serial synchrotron crystallography, we visualized half-of-the-sites reactivity and correlated molecular-breathing motions in the enzyme fluoroacetate dehalogenase. Eighteen time points from 30 milliseconds to 30 seconds cover four turnover cycles of the irreversible reaction. They reveal sequential substrate binding, covalent-intermediate formation, setup of a hydrolytic water molecule, and product release. Small structural changes of the protein mold and variations in the number and placement of water molecules accompany the various chemical steps of catalysis. Triggered by enzyme-ligand interactions, these repetitive changes in the protein framework’s dynamics and entropy constitute crucial components of the catalytic machinery.

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