Targeting SurA Dynamics: An Achilles Heel in Bacterial Outer Membrane Biogenesis

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In February 2017 the World Health Organisation published its first ever list of antibiotic-resistant "priority pathogens" - a catalogue of 12 families of bacteria that pose the greatest threat to human health. Of these, 9 are Gram-negative bacteria. The outer membrane (OM) of Gram-negative bacteria protects them from potentially damaging molecules such as antibiotics. The OM is packed with outer membrane proteins (OMPs), creating a permeability barrier that is critical for bacterial survival and endows bacterial resistance to many types of antibiotics. Breaking this barrier is thus an attractive route towards the generation of new antibacterial agents. The biosynthesis of OMPs starts in the cytoplasm and ends with their folding and insertion into the OM, where they form cylindrical, barrel-like structures. The molecular chaperone SurA escorts these newly made unfolded OMPs through the periplasm to the OM. Perturbing SurA chaperone function leads to a loss of bacterial viability and affects antibiotic resistance, demonstrating that SurA is an attractive target to control Gram-negative pathogens. One of the current challenges of effective manipulation of SurA activity is our very limited understanding of the molecular basis of how this large, multidomain chaperone machine works to ensure the safe journey of OMPs through the periplasm. While the crystal structure of SurA is known, a wealth of evidence suggests that SurA function predominantly relies on dynamic motions in SurA involving interdependent rearrangements of its three domains and their transient interactions with unfolded OMPs. In this proposal we will exploit the very latest, exciting, developments in solution nuclear magnetic resonance (NMR), along with other biophysical and computational techniques and functional assays in test tubes and in living bacteria, that will enable us to 'watch' the dynamic SurA chaperone machinery in action with atomic resolution. Using these experiments we will be able to understand how conformational rearrangements in SurA enable its chaperone function. In addition, we will elucidate how the transient and dynamic interactions between SurA and its OMP substrates enable efficient substrate recognition and prevent OMP aggregation. Finally, we will explore how SurA function and OMP biosynthesis can be controlled in vivo, paving the way towards new antibacterial agents that impair how pathogenic bacteria build their OM, weakening their defences against antibiotics.