MOMP from Campylobacter jejuni is a trimer of 18-stranded β-barrel monomers with a Ca(2+) ion bound at the constriction zone. by Ferrara, L, Wallat, G, Moynié, L, Dhanasekar, N, Aliouane, S, Acosta-Gutiérrez, S, Pagès, J, Bolla, J, Winterhalter, M, Ceccarelli, M, Naismith, J