Browsing by Author "Ladbury, John E."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Grb2 monomer–dimer equilibrium determines normal versus oncogenic function
    (Macmillan Publishers Limited, 2015) Ahmed, Zamal; Timsah, Zahra; Suen, Kin M.; Cook, Nathan P.; Lee, Gilbert R. IV; Lin, Chi-Chuan; Gagea, Mihai; Marti, Angel A.; Ladbury, John E.
    The adaptor protein growth factor receptor-bound protein 2 (Grb2) is ubiquitously expressed in eukaryotic cells and involved in a multitude of intracellular protein interactions. Grb2 plays a pivotal role in tyrosine kinase-mediated signal transduction including linking receptor tyrosine kinases to the Ras/mitogen-activated protein (MAP) kinase pathway, which is implicated in oncogenic outcome. Grb2 exists in a constitutive equilibrium between monomeric and dimeric states. Here we show that only monomeric Grb2 is capable of binding to SOS and upregulating MAP kinase signalling and that the dimeric state is inhibitory to this process. Phosphorylation of tyrosine 160 (Y160) on Grb2, or binding of a tyrosylphosphate-containing ligand to the SH2 domain of Grb2, results in dimer dissociation. Phosphorylation of Y160 on Grb2 is readily detectable in the malignant forms of human prostate, colon and breast cancers. The self-association/dissociation of Grb2 represents a switch that regulates MAP kinase activity and hence controls cancer progression.
  • Thumbnail Image
    Item
    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).
  • Thumbnail Image
    Item
    Targeting the Src Homology 2 (SH2) Domain of Signal Transducer and Activator of Transcription 6 (STAT6) with Cell-Permeable, Phosphatase-Stable Phosphopeptide Mimics Potently Inhibits Tyr641 Phosphorylation and Transcriptional Activity
    (American Chemical Society, 2015) Mandal, Pijus K.; Morlacchi, Pietro; Knight, J. Morgan; Link, Todd M.; Lee, Gilbert R. IV; Nurieva, Roza; Singh, Divyendu; Dhanik, Ankur; Kavraki, Lydia; Corry, David B.; Ladbury, John E.; McMurray, John S.
    Signal transducer and activator of transcription 6 (STAT6) transmits signals from cytokines IL-4 and IL-13 and is activated in allergic airway disease. We are developing phosphopeptide mimetics targeting the SH2 domain of STAT6 to block recruitment to phosphotyrosine residues on IL-4 or IL-13 receptors and subsequent Tyr641 phosphorylation to inhibit the expression of genes contributing to asthma. Structure–affinity relationship studies showed that phosphopeptides based on Tyr631 from IL-4Rα bind with weak affinity to STAT6, whereas replacing the pY+3 residue with simple aryl and alkyl amides resulted in affinities in the mid to low nM range. A set of phosphatase-stable, cell-permeable prodrug analogues inhibited cytokine-stimulated STAT6 phosphorylation in both Beas-2B human airway cells and primary mouse T-lymphocytes at concentrations as low as 100 nM. IL-13-stimulated expression of CCL26 (eotaxin-3) was inhibited in a dose-dependent manner, demonstrating that targeting the SH2 domain blocks both phosphorylation and transcriptional activity of STAT6.