POTRA3s

POTRA3s are a subset of POTRA (polypeptide-transport-associated) domains, specifically the third domain found in multi-domain POTRA-containing proteins. They are most commonly discussed in the context of the Beta-barrel Assembly Machinery (BAM) complex in Gram-negative bacteria, where POTRA domains cooperate with periplasmic chaperones to guide and fold outer membrane proteins.

In terms of structure, POTRA domains are small, soluble modules of roughly 70 to 100 amino acids that form a beta-rich core. The third POTRA domain exhibits sequence conservation with other POTRA domains but also contains distinctive residues that mediate specific protein–protein interactions, particularly with substrates destined for outer membrane insertion and with BamA partner proteins such as BamD and SurA.

Functionally, POTRA3s participate in recognition and binding of nascent outer membrane proteins and in presenting them to the BamA beta-barrel for insertion into the outer membrane. Mutations in POTRA3s can impair outer membrane protein (OMP) assembly, reduce membrane integrity, and increase sensitivity to envelope stress.

Distribution across bacteria is uneven: while many components of the BAM pathway encode multiple POTRA domains, the exact set and arrangement vary by lineage. The term POTRA3s is used primarily by structural and functional studies that compare domain-specific roles within the BAM pathway.

See also BamA, SurA, and outer membrane protein assembly. Further reading includes reviews on POTRA-domain architecture and BAM complex function.