ALLOSTERIC ZINC REGULATION IN STREPTOCOCCUS PNEUMONIAE BY ADCR

DAIANA ANDREA CAPDEVILA; KATHERINE EDMONDS; JIEFEI WANG; HONGWEI WU; DAVID GIEDROC

Carbondale

Congreso; 2016 Gibbs Conference on Biothermodynamics; 2016

Gibbs Society of Biological Thermodynamics

In bacteria, metalloregulatory transcription factors are critical for maintaining transition metal ion homeostasis. These proteins allosterically link metal binding with DNA binding, thus regulating genes that control availability or efflux of that metal. AdcR is a single domain triangularly shaped homodimeric MarR-family repressor, unique in that the ligand (Zn) functions as an allosteric activator of DNA operator binding. In Zn-replete conditions, AdcR represses several genes associated with zinc uptake and availability, both required for pneumococcal virulence. A previously solved crystal structure suggests that once the protein is bound to Zn the wHTH domains adopt a favorable orientation for DNA binding. However, the structures of the Apo- and DNA-bound forms remain unknown. Here, using population-based analysis of relaxation dispersion NMR of apo-AdcR dynamics we revealed that the Apo protein is sampling different states in the s-ms time scale and that upon Zn binding to AdcR select a conformation that preferentially interacts with DNA. This Zn-induced conformational selection is accompanied by the reduction of mobility in the ps-ns on the mobile loops of the metal binding site and general reduction of side chain flexibility. Together, these data suggest that Zn binding promotes a conformational change that would reduce the entropic cost of DNA binding and freeze the protein in a conformation that has a more favorable enthalpic contribution to DNA binding.