How BamA recruits OMP substrates via poly-POTRAs domain.

Almost all the outer membrane proteins (OMPs) fold into an invariant β-barrel fold via the polypeptide-transport-associated (POTRA) motif and β-barrel assembly machinery (BAM). However, whether and how poly-POTRAs interact with OMPs remain largely unknown. Here, we have characterized the structures of Haemophilus influenzae poly-POTRAs via X-ray crystallography, small angle X-ray scattering, and molecular dynamics simulation. Unexpectedly, crystal packing reveals a putative OMP travel pathway spiraled by the conserved α2-β2 edges in poly-POTRAs. Supportively, the structure-based mutations targeting the OMP binding sites significantly disrupt OMP biogenesis, resulting in severe cell growth defects. Another notable feature in H. influenzae POTRA structures is flexibility. As characterized by ELISA assays, poly-POTRAs could recruit OMP substrates in a step-wise manner. More importantly, the restriction of POTRA-POTRA linkage and flexibility significantly impairs the BamA function and causes cell growth defect. Altogether, these results suggest that the β-strand augmentations and intrinsic flexibility are important factors for BamA-OMP recruitment.-Ma, X., Wang, Q., Li, Y., Tan, P., Wu, H., Wang, P., Dong, X., Hong, L., Meng, G. How BamA recruits OMP substrates via poly-POTRAs domain.