Porin flexibility in Providencia stuartii: cell-surface-exposed loops L5 and L7 are markers of Providencia porin OmpPst1

Epidemiologically unrelated Providencia stuartii strains isolated in hospitals in the south of France were investigated for their porin sequences and profiles. Noticeable resistance to β-lactams was found to be associated with production of extended spectrum β-lactamases or AmpC overproduction, but not metallo-β-lactamases. At the same time, the expression level of outer membrane porins was unmodified in these isolates. The identity of the amino acid sequences of the major porin OmpPst1 was less than 90% in the tested clinical strains, whereas sequences of the second major porin OmpPst2 were found to be identical in all isolates. Sequence diversity identified in the OmpPst1 porins was mainly located in two cell-surface-exposed loops (L5 and L7): these loops were found to be responsible for 80% of the main movements of the protein. Parallel tempering MD simulations indicated possible coordinated movement of these loops that might affect the electrostatic interaction of the porin with membrane components (e.g. LPS) or with external molecules/surfaces. This suggests that such flexibility of surface-exposed domains of OmpPst1 may participate in bacterial adaptation to the environment.