Integration of an Electrostatic Network and Disorder-to-Order Transitions in Protein Allostery

Abstract

Although allostery-in which action at one site alters the function at another site -is integral to many biological regulatory processes, the molecular mechanism of this phenomenon still eludes our understanding. Transcription repression by E. coli biotin repressor, BirA, is allosterically modulated by activation of dimerization via binding of the small molecule effector biotinoyl-5'-AMP. Previous studies have shown that disorder-to-order transitions in loops on the distant dimerization and effector binding surfaces communicate in BirA allostery. We hypothesize that an electrostatic network is key to this communication. In this work, combined experimental and computational methods have been applied to investigate the role of this network in BirA allostery. Energy Network Analysis predicts that the electrostatic network residues participate in a larger allosteric network, while ITC measurements support network formation in solution upon bio-5’-AMP binding. Thermodynamic measurements reveal the importance of the network for both effector binding and BirA allostery. Force Distribution Analysis combined with Energy Network Analysis show coupling between the electrostatic network and disorder-to-order transitions in BirA. The experimental and computational studies support an allosteric mechanism in which an electrostatic network enables communication, via a global population shift, between disorder-to-order transitions at two distant functional sites.