Lactococcin B Is Inactivated by Intrinsic Proteinase PrtP Digestion in Lactococcus lactis subsp. lactis BGMN1-501

In our previous study, we showed that PrtP is able to impair bacteriocin LcnB activity despite being produced by the same organism, and even if they were encoded by the same plasmid. However, exact cleavage site within LcnB bacteriocin, as well as the activity of the resulting peptides remained unknown. Here we further explored the interplay between these two proteins and defined, using mass spectrometry, that the hydrolysis occurs between the sixth and seventh amino acid on the N terminus of LcnB. Although it was suspected that the cleaved form of LcnB could retain some level of activity, both chemically synthesized and recombinant variant of truncated LcnB exhibited no antimicrobial activity. Wild type form of LcnB was recombinantly overexpressed using the same expression system, its antimicrobial activity was tested before and after the treatment with PrtP proteinase, and the degradation products were analyzed with reverse-phase high-pressure liquid chromatography. The results confirmed the inactivity of the truncated LcnB and additionally corroborated the PrtP cleavage site in LcnB bacteriocin.