Dynamic Lateral Gate of BamA and TamA Regulated by POTRA Domains

Abstract

The β-barrel assembly machinery (BAM) complex, which is responsible for the biogenesis of β-barrel membrane proteins, is thought to function through the lateral gating of its central component BamA. BamA contains 5 periplasmic polypeptide-transport-associated (POTRA) domains and a transmembrane β-barrel. However, how the lateral gate of the β-barrel is regulated and promotes the insertion of nascent substrate β-barrels remains unknown. To elucidate the mechanism, we carry out 36 μs of equilibrium simulations of BamA with and without POTRA domains from Escherichia coli, Salmonella enterica, Haemophilus ducreyi and Neisseria gonorrhoeae, together with BamA's homolog, TamA, of Escherichia coli in their native membranes. From these equilibrium simulations, we observe membrane thinning near the lateral gate in all of our systems, while unexpectedly TamA systems also have a thinner membrane at the opposite side of lateral gate. We also see occasional spontaneous lateral gate opening and sliding of the β-strands at the gate, indicating that the lateral gate is dynamic. Additionally, PMF calculations for lateral gate opening for all of our systems suggest that POTRA domains play an important role in regulating lateral gate opening.