Structure and activity of a class II lanthipeptide from a thermophilic bacterium

Lanthipeptides represent the largest group of ribosomally synthesized and post-translationally modified peptides (RiPPs). Lanthipeptides offer promising avenues for discovering new antibacterial and antifungal agents. Here, we identify and structurally analyze the product of the tla BGC, which encodes a class II lanthipeptide in the thermophilic bacterium Thermoactinomyces sp. DSM 45891. Heterologous co-expression of the lanthipeptide synthetase TlaM resulted in modification of the two precursor peptides TlaA1 and TlaA2, which share 58% identity. TlaA1 was dehydrated seven times and TlaA2 six times. In both peptides, four thioether rings were formed with two overlapping DL-(methyl)lanthionine rings at the C-terminus. Both peptides also contain two central and N-terminal non-overlapping DL-methyllanthionines. These findings demonstrate that these peptides deviate from the general rule of stereoselective LL-(methyl)lanthionine formation from a DhxDhxXxxXxxCys motif (Dhx = dehydroalanine or dehydrobutyrine). AspN-cleaved TlaM-modified TlaA1 displayed anti-microbial activity against a subset of bacteria including Gram-negative ESKAPE pathogens. We named the lantibiotic thermolanthin.