Potential contacts between the M regions with increased deuterium uptake (magenta: active site residues; red: other M residues) and the other regions of the M domain in the presence of scFv3-1. Zinc ion is depicted as a green sphere. (A) A polar contact between the side chain of Asn107 in the α2 helix and the backbone of Gly219 in the α4 helix, which contains 3 of the 4 residues in the active site, is illustrated. (B) Polar contacts between the side chain of Gln269 in the α5 helix and the backbone of Glu233 immediately N-terminal to His234, which helps coordinate the zinc ion; and the side chains of α5 residues S263 and S266 with the side chain of Asp235 immediately C-terminal to His234, are illustrated.