Entropy Redistribution Drives Allostery in Transcriptional Regulators from Bacteria

CAPDEVILA, DAIANA A; DAVID GIEDROC

Grosseto

Workshop; Challenges for magnetic resonance in life sciences; 2018

EMBO

The concept of allostery is foundational to the field of structural biology and lies at the centerof biological regulation in complex systems biology. Technical advances in NMR spectroscopyhave made it possible to interrogate the role of dynamics rather than merely describe structuralchanges in mechanisms of allosteric control.Here, we propose a model of allostery in a compact, single domain metalloregulatory proteinthat can be entirely explained by a redistribution of site-specific conformational entropy. Weuse a well-developed model system, a zinc (Zn)-sensing transcriptional repressor from thehuman bacterial pathogen Staphylococcus aureus (CzrA), to provide unprecedented insightsinto 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 forconformational entropy (ΔSconf), we show that Zn binding renders inaccessible a highlydynamic 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 allostericregulation. While the role of solvent is generally well understood in regulatory eventsassociated with major protein structural rearrangements, the degree to which protein dynamicsimpact water degrees of freedom is unclear. We show that non-native residue-specificdynamics in allosterically impaired CzrA mutants are coupled to significant perturbations insolvent entropy. We conclude that functional dynamics are not necessarily restricted to proteinresidues, but involve surface water molecules that are coupled to protein internal motions.Finally, we will discuss how nature tunes site-specific backbone and sidechain dynamics todrive allosteric activation in the Zn uptake repressor (AdcR), from Streptococcus pneumoniae.