Hinge Twists and Population Shifts Deliver Regulated Catalysis for ATP-PRT in Histidine Biosynthesis.

Allosteric regulation plays an important role in the control of metabolic flux in biosynthetic pathways. In microorganisms, many enzymes in these pathways adopt different strategies of allostery to allow the tuning of their activities in response to metabolic demand. Thus, it is important to uncover the mechanism of allosteric signal transmission to fully comprehend the complex control of enzyme function and its evolution. ATP-phosphoribosyltransferase (ATP-PRT), as the first enzyme in the histidine biosynthetic pathway, is allosterically regulated by histidine and offers a good platform for the study of allostery. Two forms of ATP-PRT, namely long and short forms, were discovered that show different arrangements of their regulatory machinery. Crystal structures of the long-form ATP-PRT have revealed overall conformational changes in the inhibited state, but the observed changes in the active state are quite subtle, making the elucidation of its allosteric mechanism difficult. Here, we combine computational methods (ligand docking, quantum mechanics/molecular mechanics optimization, and molecular dynamic simulations) with experimental studies to probe the signal transmission between remote allosteric and active sites. Our results reveal that distinct conformational ensembles of the catalytic domain with different dynamic properties exist in the ligand-free and histidine-bound enzymes. These ensembles display different capabilities in supporting the catalytic and allosteric function of ATP-PRT. The findings give insight into the underlying mechanism of allostery and allow us to propose that the hinge twisting within the catalytic domain is the key for both enhancement of catalysis and provision of regulation in ATP-PRT enzymes.