The periplasmic chaperone SurA plays a key role in outer membrane protein (OMP) biogenesis. E. coli SurA comprises a core domain and two peptidylprolyl isomerase domains (P1 and P2), but its mechanisms of client binding and chaperone function have remained unclear. Here, we use chemical cross-linking, hydrogen-deuterium exchange mass spectrometry, single-molecule FRET and molecular dynamics simulations to map the client binding site(s) on SurA and interrogate the role of conformational dynamics in OMP recognition. We demonstrate that SurA samples an array of conformations in solution in which P2 primarily lies closer to the core/P1 domains than suggested in the SurA crystal structure. OMP binding sites are located primarily in the core domain, and OMP binding results in conformational changes between the core/P1 domains. Together, the results suggest that unfolded OMP substrates bind in a cradle formed between the SurA domains, with structural flexibility between domains assisting OMP recognition, binding and release.

Astbury Centre for Structural Molecular Biology and School of Medicine University of Leeds Leeds LS2 9JT UK

Astbury Centre for Structural Molecular Biology School of Chemistry University of Leeds Leeds LS2 9JT UK

Astbury Centre for Structural Molecular Biology School of Molecular and Cellular Biology Faculty of Biological Sciences University of Leeds Leeds LS2 9JT UK

Faculty of Science University of South Bohemia Ceske Budejovice Czech Republic

National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health Bethesda MD 20892 USA

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