Project description:Tripartite resistance nodulation and cell division multidrug efflux pumps span the periplasm and are major drivers of multidrug resistance among Gram-negative bacteria. Cations, such as Mg2+, become concentrated within the periplasm and, in contrast to the cytoplasm, it’s pH is sensitive to conditions outside the cell. Here, we reveal an interplay between Mg2+ and pH in modulating the structural dynamics of the periplasmic adaptor protein, AcrA, and its function within the prototypical AcrAB-TolC multidrug pump from Escherichia coli. In the absence of Mg2+, AcrA becomes increasingly plastic within acidic conditions, but when Mg2+ is bound this is ameliorated, resulting instead in domain specific organisation. We establish a unique histidine residue directs these dynamics and is essential for sustaining pump activity across acidic, neutral, and basic regimes. Overall, we propose Mg2+ conserves AcrA structural mobility to ensure optimal AcrAB-TolC function within rapid changing environments commonly faced during bacterial infection and colonization.
Project description:Membrane efflux pumps play a major role in bacterial multidrug resistance. The tripartite multidrug efflux pump system from Escherichia coli, AcrAB-TolC, is a target for inhibition to lessen resistance development and restore antibiotic efficacy, with homologs in other ESKAPE pathogens. Here, we rationalize a mechanism of inhibition against the periplasmic adaptor protein, AcrA, using a combination of hydrogen/deuterium exchange mass spectrometry, cellular efflux assays, and molecular dynamics simulations. We define the structural dynamics of AcrA and find that an inhibitor can inflict long-range stabilisation across all four of its domains, whereas an interacting efflux substrate has minimal effect. Our results support a model where an inhibitor forms a molecular wedge within a cleft between the lipoyl and αβ domains of AcrA, diminishing its conformational transmission of drug-evoked signals from AcrB to TolC. This work provides molecular insights into multidrug adaptor protein function which could be valuable for developing antimicrobial therapeutics.
Project description:Hydrogen deuterium exchange mass spectrometry of HSL in the presence of artificial lipid droplets to analyze lipid droplets binding.
Project description:Bacteria have evolved numerous biochemical processes that underpin their biology and pathogenesis. The small, non-enzymatic bacterial (Salmonella) effector SteE mediates kinase reprogramming, whereby the canonical serine/threonine host kinase GSK3 gains tyrosine-directed activity towards neosubstrates, promoting Salmonella virulence. Yet, both the mechanism behind the switch in GSK3’s activity and the diversity of this phenomenon remain to be determined. Here we show that kinase reprogramming of GSK3 is mediated by putative homologues from diverse Gram-negative pathogens. Next, we identify both the molecular basis of how SteE targets GSK3 and then uncover that the SteE-induced tyrosine activity conferred on GSK3 occurs by mimicry of an L/xGxP motif, previously shown to mediate GSK3 autophosphorylation on a tyrosine. Together, we demonstrate how a family of intrinsically disordered proteins mediate kinase reprogramming through the molecular mimicry of eukaryotic short linear motifs. With these advances comes the potential for the rationale design of synthetic reprogramming proteins
Project description:Harnessing the potential beneficial effects of kinase signalling through the generation of direct kinase activators remains an underexplored area of drug development. This also applies to the PI 3-kinase (PI3K) signalling pathway which has been extensively targeted by inhibitors for conditions with PI3K overactivation, such as cancer and immune dysregulation1-3. Here we report on the discovery of UCL-TRO-1938 (further referred to as 1938), a small molecule activator of the PI3Kα isoform, a critical effector of growth factor signalling. 1938 allosterically activates PI3Kα through a unique mechanism, by enhancing multiple steps of the PI3Kα catalytic cycle, and causes both local and global conformational changes in the PI3Kα structure. This compound is selective for PI3Ka over other PI3K isoforms and multiple protein and lipid kinases. It transiently activates PI3K signalling in all rodent and human cells tested, resulting in cellular responses such as proliferation and neurite outgrowth. In rodent models, acute treatment with 1938 provides cardioprotection from ischaemia reperfusion injury and, upon local administration, enhances nerve regeneration following nerve crush. This study identifies a unique chemical tool to directly probe PI3Kα signalling and a novel approach to modulate PI3K activity, widening the therapeutic potential of targeting these enzymes, through short-term activation for tissue protection and regeneration. Our findings illustrate the potential of activating kinases for therapeutic benefit, a currently largely untapped area of drug development.
Project description:Hydrogen/deuterium exchange (HDX) methods for studying protein dynamics would benefit from millisecond-scale incubations to probe intrinsically disordered proteins, highly dynamic regions and conformation changes. Here we investigate droplet microfluidics for rapid mixing to trigger D2O labelling, uniform incubations and rapid droplet merging for acid quenching in advance of mass spectrometry. A surfactant-free merging approach combining expansion elements for synchronised droplet collision proved robust. The high diffusive flux of D2O and protons enable microsecond mixing to trigger and arrest D2O labelling, respectively, affording the possibility of single millisecond incubations. Millisecond droplet HDX processors were used to measure forward exchange and demonstrate that D2O labelling is the rate-limiting step, in essence defining 10 milliseconds as the minimum practical incubation time. With the ability to access millisecond time scales the fast dynamics of calmodulin, a model of calcium-triggered allostery with rapid conformational switching, was investigated. Calcium binding increases D2O accessibility to the linker region, reporting the flexibility which enables the scissor-like motion of calmodulin for capturing proteins. The millisecond precision of droplet microfluidic HDX paves the way to advance our understanding of protein structural dynamics.
Project description:The Rag GTPases recruit the master kinase mTORC1 to lysosomes to regulate cell growth and proliferation in response to amino acid availability. The nucleotide state of Rag heterodimers is critical for their association with mTORC1. Our cryo-EM structure of RagA/RagC in complex with mTORC1 shows the details of RagA/C binding to the RAPTOR subunit of mTORC1 and explains why only the RagAGTP/RagCGDP nucleotide state binds mTORC1. Previous kinetic studies suggested that GTP binding to one Rag locks the heterodimer to prevent GTP binding to the other. Our crystal structures and dynamics show the mechanism for this locking, and explain how oncogenic hotspot mutations disrupt this process. In contrast to allosteric activation by RHEB, Rag heterodimer binding does not change mTORC1 conformation and activates mTORC1 by targeting it to lysosomes.
Project description:The enzyme glutamate decarboxylase (GAD) produces the neurotransmitter GABA, using pyridoxal-5’-phosphate. GAD exists as two isoforms, GAD65 and GAD67. Only GAD65 acts as a major autoantigen, with its autoantibodies frequently found in type 1 diabetes and other autoimmune diseases. Here we characterize the structure and dynamics of GAD65 and its interaction with the autoimmune polyendocrine syndrome type 2-associated autoantibody b96.11. Combining hydrogen-deuterium exchange mass spectrometry (HDX), X-ray crystallography, cryo-electron microscopy and computational approaches, we dissect the conformational dynamics of the inactive apo- and the active holo-forms of GAD65, as well as the structure of the GAD65-autoantibody complex. HDX reveals the local dynamics that accompany autoinactivation, with the catalytic loop playing a key role in promoting collective dynamics at the interface between CTD and PLP domains. In the GAD65-b96.11 complex, heavy chain CDRs dominate the interaction, with the relatively long CDRH3 at the interface centre and uniquely bridging the GAD65 dimer via extensive electrostatic interactions with the 260PEVKEK265 motif. The autoantibody bridges structural elements on GAD65 that contribute to conformational change in GAD65, thus connecting the unique and intrinsic conformational flexibility that governs the autoinactivation mechanism of the enzyme to its autoantigenicity. The intrinsic dynamics, rather than sequence differences within epitopes, appear to be responsible for the contrasting autoantigenicities of GAD65 and GAD67.
Project description:Muscarinic acetylcholine receptor M3 (M3) and its downstream effector Gq/11 are critical drug development targets given their involvement in numerous physiological processes and diseases. Although a cryo-electron microscopy study previously defined the structure of the M3-miniGq complex, the lack of information on the intracellular loop 3 (ICL3) of M3 and α-helical domain (AHD) of Gαq has made it difficult to comprehend the molecular mechanism of M3-Gq coupling fully. Here, we present the molecular mechanism underlying the dynamic interactions between the wild-type full-length M3 and heterotrimeric Gq using hydrogen-deuterium exchange mass spectrometry and NanoLuc Binary Technology-based cell systems. This study suggests potential binding interfaces between M3 and Gq in pre-assembled and fully active nucleotide-free complexes. In addition to well-known binding interfaces, we observed the interaction of long ICL3 with Gβγ. Furthermore, M3 ICL3 negatively affected M3-Gq coupling, and the Gαq AHD underwent unique conformational changes during M3-Gq coupling. Therefore, we propose a comprehensive molecular mechanism of M3-Gq coupling by analyzing previously well-defined binding interfaces and neglected regions, such as M3 ICL3 and the Gαq AHD.
Project description:Nuclear receptors function as ligand-regulated transcription factors whose ability to regulate diverse physiological processes is closely linked with conformational changes induced upon ligand binding. Understanding how conformational populations of nuclear receptors are shifted by various ligands could illuminate strategies for the design of synthetic modulators to regulate specific transcriptional programs. Here, we investigate ligand-induced conformational changes using a reconstructed, ancestral nuclear receptor. By making substitutions at a key position, we engineer receptor variants with altered ligand specificities. We use atomistic molecular dynamics (MD) simulations with enhanced sampling to generate ensembles of wildtype and engineered receptors in combination with multiple ligands, followed by conformational analysis and prediction of ligand activity. We combine cellular and biophysical experiments to allow correlation of MD-based predictions with functional ligand profiles, as well as elucidation of mechanisms underlying altered transcription in receptor variants. We determine that conformational ensembles accurately predict ligand responses based on observed population shifts, even within engineered receptors that were constitutively active or transcriptionally unresponsive in experiments. These studies provide a platform which will allow structural characterization of physiologically-relevant conformational ensembles, as well as provide the ability to design and predict transcriptional responses in novel ligands.