FUNCTIONAL ROLE OF SOLVENT ENTROPY AND CONFORMATIONAL ENTROPY OF METAL BINDING IN A DYNAMICALLY-DRIVEN ALLOSTERIC SYSTEM

CAPDEVILA, DAIANA A; DAVID GIEDROC

Birmingham

Conferencia; European Biological Inorganic Chemistry Conference; 2018

Society European Biological Inorganic Chemistry

The concept of allostery is foundational to the field of structural biology and lies at the center of biological regulation in complex systems biology. Technical advances in NMR spectroscopy have made it possible to interrogate the role of dynamics rather than merely describe structural changes in mechanisms of allosteric control. Here, we propose a model of allostery in a compact, single domain metalloregulatory protein that can be entirely explained by a redistribution of site-specific conformational entropy. We use a well-developed model system, a zinc (Zn)-sensing transcriptional repressor from the human bacterial pathogen Staphylococcus aureus (CzrA), to provide unprecedented insights into heterotropic allostery, the inhibition of DNA operator binding by the allosteric ligand Zn. By employing order parameter measurements (S2axis) of methyl groups as a proxy for conformational entropy (Sconf), we show that Zn binding renders inaccessible a highly dynamic DNA-bound conformation. We further show that these entropic fingerprints pinpoint ?hot spots? that when mutated, specifically impair allosteric coupling of Zn and DNA binding. We then investigated the role of solvent molecules in this dynamically driven allosteric regulation. While the role of solvent is generally well understood in regulatory events associated with major protein structural rearrangements, the degree to which protein dynamics impact water degrees of freedom is unclear. We show that non-native residue-specific dynamics in allosterically impaired CzrA mutants are coupled to significant perturbations in solvent entropy. We conclude that functional dynamics are not necessarily restricted to protein residues, but involve surface water molecules that are coupled to protein internal motions.