How nature tunes dynamics to drive allosteric inhibition vs. activation: AdcR, a Zn regulator of Streptococcus pneumoniae

CAPDEVILA, DAIANA A; DAVID GIEDROC

Florianopolis

Conferencia; ICBIC18 ? International Conference on Biological Inorganic Chemistry; 2017

Society of Biological Inorganic Chemistry

In bacteria, metalloregulatory transcription factors are critical for maintaining transition metalion homeostasis. These proteins allosterically link metal binding with DNA binding, thusregulating genes that control availability or efflux of that metal. In particular, in Zn-­repleteconditions AdcR represses several genes associated with zinc uptake and availability, bothrequired for pneumococcal virulence.AdcR is a member of the multi-­antibiotic resistance regulator (MarR) protein family thatgenerally repress the expression of drug efflux pumps in their ligand free state. AdcR is theonly known MarR family metallosensor, unique also in that the ligand (Zn) functions as anallosteric activator of DNA operator binding.Here, using a combination of NMR based techniques and SAXs we revealed that the Apoprotein has multiple independent domains connected by flexible linkers that exhibit two Znbinding sites. Upon Zn binding, the mobility of this linker is restricted leading to a change inshape and Zn-­AdcR behaves as a single domain protein. A population-­based analysis ofrelaxation dispersion NMR of apo-­AdcR dynamics showed that the Apo protein is samplingdifferent states in the ms time scale and Zn selects a conformation with higher affinity for DNA.Analysis of site specific backbone and sidechains dynamics in the ps-­ns time scale1 showedthat Zn not only induces restriction of protein dynamics (-­TDSconfor = 3.2 kcal/mol), but alsoenhances mobility in the DNA binding domain. Together, these data suggest that Zn bindingpromotes a conformational change that would reduce the entropic cost of DNA binding andenhance dynamics within the protein exclusively in the DNA binding domain poising the proteinto interact with DNA.Based on these results it can be hypothesized that the inducer can inhibit DNA binding byquenching dynamics in the DNA binding region and, on other side, act as an activator byenhancing such dynamics. An analysis of the current available crystallographic andcomputational data of MarR protein, confirms that characterized MarRs, where the inducerleads to inhibition of DNA binding, have intrinsic dynamic DNA binding domains in the apo-­form. Apo AdcR is unique in that the flexibility is restricted to the metal binding pocket and ZnIIbinding increases flexibility of a fairly rigid DNA binding domain.Acknowledgments: US National Institutes of Health (GM118157) and the Pew FoundationReferences:[1] Capdevila, D. A.;; Braymer, J. J.;; Edmonds, K. A.;; Wu, H.;; Giedroc, D. P. Proc Natl AcadSci U S A 2017, in the press (doi: 10.1073/pnas.1620665114)