Location: Infectious Bacterial Diseases ResearchTitle: Cell wall peptidolipids of Mycobacterium avium: from genetic prediction to exact structure of a nonribosomal peptide Author
Submitted to: Molecular Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2017
Publication Date: 6/15/2017
Citation: Bannantine, J.P., Etienne, G., Laval, F., Lemassu, A., Daffe, M., Bayles, D.O., Ganneau, C., Bonhomme, F., Branger, M., Cochard, T., Bay, S., Biet, F., Stabel, J.R. 2017. Cell wall peptidolipids of Mycobacterium avium: from genetic prediction to exact structure of a nonribosomal peptide. Molecular Microbiology. 105(4):525-539. https://doi.org/10.1111/mmi.13717. Interpretive Summary: This study focuses on non-ribosomal peptides of a significant bacterial pathogen of cattle and sheep which has a multi-million dollar economic toll in commercial livestock industries worldwide (Mycobacterium avium subspecies paratuberculosis which causes Johne's disease). Specifically, we have discovered and linked a defined genetic difference with a resulting phenotype and we have uncovered a new molecular signature of Mycobacterium that may form the basis in the patho-adaptation of this bacteria. Using an original approach by reverse genetics, we have discovered that specific surface-exposed lipopeptides exist in different forms within highly related subspecies of Mycobacterium avium. This finding was first suggested by our discovery of a previously unknown large sequence change (polymorphism) within a single, large nonribosomal peptide synthase gene. This large polymorphism suggests that all ovine strains (S-type) synthesize a lipotripeptide, compared to the lipopentapeptide known to exist in bovine strains (C-type). The exact structural formula of this unique lipid antigen was conclusively established using multiple physico-chemical approaches. Chemical synthesis of the predicted S-type lipotripeptide, and comparison with the purified natural antigen by thorough biochemical and physico-chemical analyses, demonstrated that typical lipopeptides from this bacteria are indeed different in S-type (lipotripeptide) and C-type strains (lipopentapeptide). These data, in addition to providing a new advancement on how mycobacteria can change their cell wall, also may demonstrate a role of the mycobacterial lipopeptides in evolution toward host specificity (sheep versus cattle) and disease presentation. These findings are of interest primarily to other scientists working in the field.
Technical Abstract: Total lipids from an M. avium subsp. paratuberculosis (Map) ovine strain (S-type) contained no identifiable glycopeptidolipids or lipopentapeptide, yet both lipids are present in other M. avium subspecies. We determined the genetic and phenotypic basis for this difference using sequence analysis and biochemical approaches. This strategy showed that a nonribosomal peptide synthase, encoded by mps1, contains three amino acid specifying modules in all ovine strains analyzed, compared to five modules in bovine strains (C-type). Sequence analysis predicted these modules would produce the tripeptide Phe-N-Methyl-Val-Ala with a lipid moiety, termed lipotripeptide (L3P). Comprehensive physico-chemical analysis of Map S397 extracts confirmed the structural formula of the native L3P as D-Phe-N-Methyl-LVal-L-Ala-OMe attached in N-ter to a 20-carbon fatty acid chain. These data demonstrate that Map S-type strains, which are more adapted in sheep, produce a unique lipid, termed L3P. Implications for these lipid differences may include pathoevolution toward host specificity and disease presentation.