Molecular mechanisms underlying the structural diversity of rhamnose-rich cell wall polysaccharides in lactococci - Dynamique de la Paroi Bactérienne
Article Dans Une Revue Journal of Biological Chemistry Année : 2024

Molecular mechanisms underlying the structural diversity of rhamnose-rich cell wall polysaccharides in lactococci

Résumé

In Gram-positive bacteria, cell wall polysaccharides (CWPS) play critical roles in bacterial cell wall homeostasis and bacterial interactions with their immediate surroundings. In lactococci, CWPS consist of two components: a conserved rhamnan embedded in the peptidoglycan layer and a surface-exposed polysaccharide pellicle (PSP), which are linked together to form a large rhamnose-rich CWPS (Rha-CWPS). PSP, whose structure varies from strain to strain, is a receptor for many bacteriophages infecting lactococci. Here, we examined the first two steps of PSP biosynthesis, using in vitro enzymatic tests with lipid acceptor substrates combined with LC-MS analysis, AlfaFold2 modeling of protein 3D-structure, complementation experiments, and phage assays. We show that the PSP repeat unit is assembled on an undecaprenyl-monophosphate (C55P) lipid intermediate. Synthesis is initiated by the WpsA/WpsB complex with GlcNAc-P-C55 synthase activity and the PSP precursor GlcNAc-P-C55 is then elongated by specific glycosyltransferases that vary among lactococcal strains, resulting in PSPs with diverse structures. Also, we engineered the PSP biosynthesis pathway in lactococci to obtain a chimeric PSP structure, confirming the predicted glycosyltransferase specificities. This enabled us to highlight the importance of a single sugar residue of the PSP repeat unit in phage recognition. In conclusion, our results support a novel pathway for PSP biosynthesis on a lipid-monophosphate intermediate as an extracellular modification of rhamnan, unveiling an assembly machinery for complex Rha-CWPS with structural diversity in lactococci.
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hal-04516979 , version 1 (28-03-2024)

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Hugo Guérin, Pascal Courtin, Alain Guillot, Christine Péchoux, Jennifer Mahony, et al.. Molecular mechanisms underlying the structural diversity of rhamnose-rich cell wall polysaccharides in lactococci. Journal of Biological Chemistry, 2024, 300 (1), pp.105578. ⟨10.1016/j.jbc.2023.105578⟩. ⟨hal-04516979⟩
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