Tuning site-specific dynamics to drive allosteric activation vs. inhibition

CAPDEVILA, DAIANA A; DAVID GIEDROC

Laurence

Conferencia; 2017 GRASP NMR; 2017

GRASP

MarR (multiple antibiotic resistance repressor) family proteins are bacterial transcriptional repressors that regulate gene expression in response to a wide range of chemical signals. Understanding how transcriptional regulators have evolved requires a comprehensive analysis of the structural and dynamical changes that occur upon inducer and DNA binding. Although there are more than 140 crystal structures of MarR family repressors in different allosteric states, the role of atomic motions in MarRs remains unexplored. Here, we provide the first experimental evidence that internal dynamics play a crucial functional role in MarR proteins, and may have played a significant role in the evolution of new biological outputs. We focused on AdcR (adhesin-competence repressor) which regulates Zn homeostasis in Streptococcus pneumoniae, to combat host-induced nutritional immunity. AdcR is of interest as the only member of the MarR family in which the inducer functions as an allosteric activator, rather than inhibitor, of DNA operator binding. The structure of the dimeric Zn bound state is known, but the mode of allosteric activation of DNA binding by Zn remains unclear. We show that an interplay between interdomain and site specific dynamics drives positive allosteric coupling of Zn coordination and DNA binding. Structural differences between the apo- and Zn-states of AdcR in solution reveal that Zn coordination triggers a transition from independent domains to a more compact structure. Residue-specific backbone and sidechain dynamics identify residues that impact the allosteric coupling free energy (∆Gc) in significant and distinct ways, based on the effect of Zn binding on either fast (∆S2axis) or slow (∆Rex) timescale dynamics. These findings reconcile the distinct mechanisms proposed for other MarRs and explain how evolution can conserve the same molecular scaffold while tuning dynamics to construct an allosteric activator from what is otherwise an allosteric inhibitor.