Mode of action and bioengineering of RumC sactipeptides to overcome antibiotic resistance of Gram-positive bacteria – RUMisBAC

Since the discovery of penicillin, humans have widely developed and used antibiotics to protect themselves from microbial infections. However, the intensive use or misused of these compounds has led to the emergence of pathogens resistant to all classes of antibiotics. This major public health threat is prompting scientists to search for new molecules, ideally natural ones, with different structures and modes of action to counter resistance phenomena evolutionary developed. A promising alternative is antimicrobial peptides (AMPs). In this context, bacteria are a treasure trove of multiple classes of naturally occurring antimicrobial peptides, more commonly known as bacteriocins. One example is ribosomally synthesized and post-translationally modified peptides (RiPPs). Of peptidic nature, their ribosomal synthesis differentiates them from conventional antibiotics. RiPPs are first synthetized in the form of a biologically inactive precursor peptide that is subjected to post-translational modifications by dedicated enzymes. Numerous studies show that the intestinal bacterial consortium, well-known as intestinal microbiome, plays a crucial role in the health of the host. For example, the barrier effect implemented by commensal bacteria is achieved through the production of bacteriocins.
RUMisBAC targets the bacterial strain Ruminococcus gnavus E1 (R. gnavus E1), a strict anaerobic Gram-positive bacterium present in the digestive tract of healthy adults. This symbiont produces five compounds belonging to the sactipeptide group, the Ruminococcins C1 to C5 (RumC1-5). This class of antimicrobial peptides involves a maturase enzyme, called sactisynthase, in the post-translational modification step, which introduces covalent thioether bonds into the substrate. More precisely, the thioether bonds of sactipeptides exclusively involve the sulfur atom of a cysteine and the??-carbon of a partner residue. The overall objective of the project, based on the very promising results reported for RumC1, is to take RumC bacteriocins one-step further towards their potential therapeutic use. The first goal is to produce and to characterize both structurally and functionally, the four remaining RumC2-5 bacteriocins. Second, to reach a more clinical level, we sought to evaluate the antimicrobial activity of RumC peptides on a wide panel of human clinical pathogens, isolated from patients, showing resistance and multidrug resistance to the major antibiotics currently used in therapy. Taking into account the bactericidal effect of RumC1 and the lack of toxic effects on eukaryotic cells, a major objective is to evaluate the antimicrobial efficacy of RumC peptides in an in vivo context by using animal models of infection. Another key point of the proposal is to elucidate the mode of action of RumC1 at the molecular level and to identify its molecular target. The successful identification of the cellular target combined with docking experiments will allow the design and the chemical synthesis of RumC biomimetic peptides.