THERMOPHILIN-13, A NONTYPICAL ANTILISTERIAL PORATION COMPLEX BACTERIOCIN, THAT FUNCTIONS WITHOUT A RECEPTOR

A novel broad host range antimicrobial substance, Thermophilin 13, has been isolated and purified from the growth medium of Streptococcus th ermophilus. Thermophilin 13 is composed of the antibacterial peptide T hmA (M-r of 5776) and the enhancing factor ThmB (M-r of 3910); the lat ter peptide increased the activity of ThmA similar to 40 x, Both pepti des are encoded by a single operon, and an equimolar ratio was optimal for Thermophilin 13 activity, Despite the antilisterial activity of T hermophilin 13, neither ThmA nor ThmB contain the YGNGV-C consensus se quence of Listeria active peptides, and post-translational modificatio ns comparable to that in the lantibiotics are also absent, Mass spectr ometry did reveal the apparent oxidation of methionines in ThmA, which resulted in a peptide that could not be enhanced any longer by ThmB, whereas the intrinsic bactericidal activity was normal, Thermophilin 1 3 dissipated the membrane potential and the pH gradient in liposomes, and this activity was independent of membrane components from a sensit ive strain (e.g. lipid or proteinaceous receptor), Models of possible poration complexes formed are proposed on the basis of sequence compar isons, structure predictions, and the functional analysis of Thermophi lin 13.