Calcium binding site in AA10 LPMO from Vibrio cholerae suggests modulating effects during environment survival and infection

Despite major efforts towards its eradication, cholera remains a major health and economic burden in many developing countries. Between outbreaks, the bacterium responsible for the disease, Vibrio cholerae, survives in aquatic environmental reservoirs, where it commonly forms biofilms, e.g., on zooplankton. N-acetyl glucosamine binding protein A (GbpA) is an adhesin that binds to the chitinaceous surface of zooplankton and breaks its dense crystalline packing thanks to its lytic polysaccharide monooxygenase (LPMO) activity, which provides V. cholerae with nutrients. In addition, GbpA is an important colonization factor associated with bacterial pathogenicity, allowing the binding to mucins in the host intestine. Here, we report the discovery of a cation-binding site in proximity of the GbpA active site, which allows Ca2+, Mg2+ or K+ to bind close to its carbohydrate-binding surface. In addition to the X-ray crystal structures, we explored how the presence of ions affects the stability of the protein, compared the new GbpA LPMO structures to those of other LPMOs, and discussed the relevance of our discovery for bacterial survival. Calcium ions, abundant in natural sources of chitin, have been found to have the strongest effect on GbpA stability. Our findings suggest a V. cholerae-specific cation-binding site in GbpA that may fine-tune activity and binding to the different substrates during environmental survival and host infection.