8.B.43.  The Bacteriocin Immunity Protein (BIP) Family 

Pediocin-like bacteriocins, also designated class IIa bacteriocins, are ribosomally synthesized antimicrobial peptides targeting species closely related to the producers. They act on the cytoplasmic membranes of Gram-positive cells by dissipating the transmembrane electrical potential through pore formation with the mannose phosphotransferase system (man-PTS) as the target/receptor. Bacteriocin-producing strains also synthesize a cognate immunity protein that protects them against their own bacteriocins. Zhu et al. 2022 reported the cryo-EM structure of the bacteriocin-receptor-immunity ternary complex from Lactobacillus sakei. The complex structure reveals that pediocin-like bacteriocins bind to the same position on the Core domain of the man-PTS, while the C-terminal helical tails of bacteriocins delimit the opening range of the Core domain away from the V-motif domain to facilitate transmembrane pore formation. Upon attack of bacteriocins from the extracellular side, the man-PTS exposes its cytosolic side for recognition of the N-terminal four-helix bundle of the immunity protein. The C-terminal loop of the immunity protein then inserts into the pore and blocks leakage induced by bacteriocins (Zhu et al. 2022).