X-ray crystal structure of 5/B/6 MBL shows the typical MBL fold.

Secondary structural elements are colored deep teal for beta sheets and orange for alpha helices; whereas, turns/coils are colored grey and the Zn2+ atoms are represented by light blue spheres. The left panel shows the overall enzyme structure with lysine residues at the allosteric site in Loop 4 (L4) and Loop 6 (L6). The right structure shows the active site residues that are responsible for coordinating the two Zn2+ ions.