Browsing by Author "Leonard, Paul G."

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    A variable DNA recognition site organization establishes the LiaR-mediated cell envelope stress response of enterococci to daptomycin
    (Oxford University Press, 2015) Davlieva, Milya; Shi, Yiwen; Leonard, Paul G.; Johnson, Troy A.; Zianni, Michael R.; Arias, Cesar A.; Ladbury, John E.; Shamoo, Yousif
    LiaR is a ‘master regulator’ of the cell envelope stress response in enterococci and many other Gram-positive organisms. Mutations to liaR can lead to antibiotic resistance to a variety of antibiotics including the cyclic lipopeptide daptomycin. LiaR is phosphorylated in response to membrane stress to regulate downstream target operons. Using DNA footprinting of the regions upstream of the liaXYZ and liaFSR operons we show that LiaR binds an extended stretch of DNA that extends beyond the proposed canonical consensus sequence suggesting a more complex level of regulatory control of target operons. We go on to determine the biochemical and structural basis for increased resistance to daptomycin by the adaptive mutation to LiaR (D191N) first identified from the pathogen Enterococcus faecalis S613. LiaRD191N increases oligomerization of LiaR to form a constitutively activated tetramer that has high affinity for DNA even in the absence of phosphorylation leading to increased resistance. Crystal structures of the LiaR DNA binding domain complexed to the putative consensus sequence as well as an adjoining secondary sequence show that upon binding, LiaR induces DNA bending that is consistent with increased recruitment of RNA polymerase to the transcription start site and upregulation of target operons.
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    An Adaptive Mutation in Enterococcus faecium LiaR Associated with Antimicrobial Peptide Resistance Mimics Phosphorylation and Stabilizes LiaR in an Activated State
    (Elsevier, 2016) Davlieva, Milya; Tovar-Yanez, Angel; DeBruler, Kimberly; Leonard, Paul G.; Zianni, Michael R.; Arias, Cesar A.; Shamoo, Yousif
    The cyclic antimicrobial lipopeptide daptomycin (DAP) triggers the LiaFSR membrane stress response pathway in enterococci and many other Gram-positive organisms. LiaR is the response regulator that, upon phosphorylation, binds in a sequence-specific manner to DNA to regulate transcription in response to membrane stress. In clinical settings, non-susceptibility to DAP by Enterococcus faecium is correlated frequently with a mutation in LiaR of Trp73 to Cys (LiaRW73C). We have determined the structure of the activated E. faecium LiaR protein at 3.2 Å resolution and, in combination with solution studies, show that the activation of LiaR induces the formation of a LiaR dimer that increases LiaR affinity at least 40-fold for the extended regulatory regions upstream of the liaFSR and liaXYZ operons. In vitro, LiaRW73C induces phosphorylation-independent dimerization of LiaR and provides a biochemical basis for non-susceptibility to DAP by the upregulation of the LiaFSR regulon. A comparison of the E. faecalis LiaR, E. faecium LiaR, and the LiaR homolog from Staphylococcus aureus (VraR) and the mutations associated with DAP resistance suggests that physicochemical properties such as oligomerization state and DNA specificity, although tuned to the biology of each organism, share some features that could be targeted for new antimicrobials.
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    Potent and selective inhibition of SH3 domains with dirhodium metalloinhibitors
    (Royal Society of Chemistry, 2015) Vohidov, Farrukh; Knudsen, Sarah E.; Leonard, Paul G.; Ohata, Jun; Wheadon, Michael J.; Popp, Brian V.; Ladbury, John E.; Ball, Zachary T.
    Src-family kinases (SFKs) play important roles in human biology and are key drug targets as well. However, achieving selective inhibition of individual Src-family kinases is challenging due to the high similarity within the protein family. We describe rhodium(II) conjugates that deliver both potent and selective inhibition of Src-family SH3 domains. Rhodium(II) conjugates offer dramatic affinity enhancements due to interactions with specific and unique Lewis-basic histidine residues near the SH3 binding interface, allowing predictable, structure-guided inhibition of SH3 targets that are recalcitrant to traditional inhibitors. In one example, a simple metallopeptide binds the Lyn SH3 domain with 6 nM affinity and exhibits functional activation of Lyn kinase under biologically relevant concentrations (EC50 200 nM).