Antimicrobial peptide active against Gram-positive bacteria (MIC=4->125 ug/ml) (PubMed:22983711). May act by forming transmembrane ion channels, since the peptide rapidly depolarizes the bacterial cytoplasmic membrane, simultaneously decreasing the membrane potential and intracellular potassium contents (PubMed:22983711). Epimerization of most, and perhaps all, L- to D-amino acids is catalyzed by PoyD, when PoyA and PoyD are coexpressed in E.coli. N-methylations are catalyzed by PoyE, when PoyA and PoyE are coexpressed in E.coli. To obtain 2-oxo-5,5-dimethylhexanoate, Thr-97 is firstly dehydrated by PoyF (PubMed:22983711). The second step possibly corresponds to methylation by PoyB/C, and the third step may be a cleavage by PoyH/J (Probable). The name 'proteusin' is inspired by Proteus, a Greek shape-shifting sea god. Compared to polytheonamide B, polytheonamide A has an additional sulfoxide moiety at Met-141, which arises from spontaneous oxidation during polytheonamide isolation.