User:Neha Priyadarshini Nayak/Sandbox

From Proteopedia

The β-barrel assembly machinery ( BAM) is a vital protein complex involved in the biosynthesis of Outer Membrane Proteins (OMPs) located in the outer surface of Gram-negative bacteria. In Neisseria gonorrhoeae, the NgBAM complex was found in an inward-open conformation, a key finding that differs from that in Escherichia coli. These OMPs play a crucial role in the survival, virulence and evasion of the host bacterium cell. The cryo-EM structure 9CN1 resolves the that mediates the folding and insertion of new OMPs in the membrane.

Bam A, an OMP, is composed of 5 N-terminal polypeptide-associated (POTRA) domains and a 16-stranded beta barrel domain at the C-terminal. These POTRA domains bind to the incoming OMP Substrates, coordinating interactions with other accessory proteins. Specifically, make extensive contact with the associated Bam D chain, thereby stabilising Bam A and positioning it for the initiation of substrate insertion. BamD acts as a regulatory scaffold, communicating the periplasm's need to the membrane barrel.

A key mechanistic feature of BamA is the dynamic formed between the strands β1 and β16 in the barrel wall. The inward-open conformation captured shows that this seam is only partially paired, leading the authors to propose a mechanism where the open seam allows the first β-strand of the incoming OMP substrate to align against BamA's β1 strand. This initial alignment then displaces β16, effectively opening the gate wider to integrate the new substrate and complete the final barrel structure. This structural insight can be examined in BamA Lateral Gate Opening, which explains how BamA begins the folding process while slightly destabilising the surrounding membrane.