Berninamycin

Propionibacterium acnes has been detected in diseased human prostate tissue, and cell culture experiments suggest that the bacterium can establish a low-grade inflammation. Here, we investigated its impact on human primary prostate epithelial cells. Microarray analysis confirmed the inflammation-inducing capability of P. acnes but also showed deregulation of genes involved in the cell cycle. qPCR experiments showed that viable P. acnes downregulates a master regulator of cell cycle progression, FOXM1. Flow cytometry experiments revealed that P. acnes increases the number of cells in S-phase. We tested the hypothesis that a P. acnes-produced berninamycin-like thiopeptide is responsible for this effect, since it is related to the FOXM1 inhibitor siomycin. The thiopeptide biosynthesis gene cluster was strongly expressed; it is present in subtype IB of P. acnes, but absent from type IA, which is most abundant on human skin. A knock-out mutant lacking the gene encoding the berninamycin-like peptide precursor was unable to downregulate FOXM1 and to halt the cell cycle. Our study reveals a novel host cell-interacting activity of P. acnes.

Berninamycin is a member of the pyridine-containing thiopeptide class of antibiotics that undergoes massive posttranslational modifications from ribosomally generated preproteins. Berninamycin has a 2-oxazolyl-3-thiazolyl-pyridine core embedded in a 35-atom macrocycle rather than typical trithiazolylpyridine cores embedded in 26-atom and 29-atom peptide macrocycles. We describe the cloning of an 11-gene berninamycin cluster from Streptomyces bernensis UC 5144, its heterologous expression in Streptomyces lividans TK24 and Streptomyces venezuelae ATCC 10712, and detection of variant and incompletely processed scaffolds. Posttranslational maturation in S. lividans of both the wild-type berninamycin prepeptide (BerA) and also a T3A mutant generates macrocyclic compounds as well as linear variants, which have failed to form the pyridine and the macrocycle. Expression of the gene cluster in S. venezuelae generates a variant of the 35-atom skeleton of berninamycin, containing a methyloxazoline in the place of a methyloxazole within the macrocyclic framework.

The mode of action of berninamycin on bacterial protein synthesis is related to that of thiostrepton, a dissimilar compound. Both antibiotics bind to the complex of 23S RNA with protein L11 and both affect various functions of the ribosomal A site. Also, Streptomyces bernensis and Streptomyces azureus (which, respectively, produce berninamycin and thiostrepton) possess similar ribosomal RNA methylases capable of rendering ribosomes resistant to these compounds. Resistance involves specific pentose-methylation of 23S ribosomal RNA.