a) Comparison of the general structures of various members of the MBL superfamily. For each protein, the characteristic MBL fold domain is indicated in green, while additional domains present in some MBL superfamily members are highlighted in other colors. Metal ions within the active site are shown as spheres, and the Zn2 (or equivalent) site is oriented towards the front. Proteins names ending in an asterisk indicate that the physiological form of protein comprises homodimers or other homooligomers, which are not shown. b) Active-site metal coordination spheres for the MBL superfamily members indicated in panel a). Zn(II), Fe(II)/Fe(III) and Mn(II) ions are represented as grey, orange and light violet spheres, respectively, while water molecules / hydroxide ions are shown as red spheres. PDB codes for the structures are: CcrA – 1ZNB, ZipD – 2CBN, SdsA1 – 2CFU, CPSF73 – 2I7V, FlRd – 4D02, GloB – 2QED, UlaG – 2WYM, PhnP – 3P2U.