Contrasting roles of dynamics in protein allostery: NMR and structural studies of CheY and the third PDZ domain from PSD-95.

Allosteric regulation is a ubiquitous phenomenon exploited in biological processes to control cells in a myriad of ways. It is also of emerging interest in the design of functional proteins and therapeutics. Even though allostery was proposed over 50 years ago and has been studied intensively from a structural perspective, many key details of allosteric mechanisms remain mysterious. Over the last decade significant attention has been paid to the "dynamic component" of allostery, as opposed to the analysis of rigid structures. Nuclear magnetic resonance spectroscopy and its ability to detect conformationally dynamic processes at atomic resolution have played an important role in expanding our understanding of allosteric mechanisms and opening up new questions. This article focuses on work that highlights how protein dynamics can factor into allosteric processes in distinct ways. Two cases are contrasted. The first considers the "traditionally allosteric" protein CheY, which undergoes a conformational change as a key element of its allostery. The second considers the more rarely observed "dynamic allostery" in a PDZ domain, in which allosteric behavior arises from changes in internal structural dynamics. Interestingly, the dynamic processes in these two contrasting examples occur on different timescales. In the case of the PDZ domain, subsequent experimental and computational work is reviewed to reveal a more complete picture of this interesting case of allostery.