Structure and Activity of Class II Lanthipeptides from a Thermophilic Bacterium

Lanthipeptides represent a large group of ribosomally synthesized and post-translationally modified peptides (RiPPs). They 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. Co-expression of the lanthipeptide synthetase TlaM with its substrates in Escherichia coli resulted in modification of the two precursor peptides TlaA1 and TlaA2, which share 58% sequence identity. TlaA1 was dehydrated up to seven times, with the major products having undergone five and six dehydrations, whereas TlaA2 was dehydrated seven 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 non-overlapping DL-methyllanthionines near the N-terminus and in the center of the peptide. These peptides deviate from the general rule of stereoselective LL-(methyl)lanthionine formation from a Dhx-Dhx-Xxx-Xxx-Cys 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.