Fig. 2.

The catalytic domain of SdsA1. (A) Cartoon with coloring as in Fig. 1. Side chains coordinating Zn ions (yellow spheres) are shown as sticks. The active-site dome (gray) is not conserved in other MBL fold enzymes. The sulfate recognition loop βN/α8 is shown in purple. (B) Structure-based sequence alignment of SdsA1 and B. fragilis β-lactamase (PDB: 1A7T). Secondary structure elements of SdsA1 are depicted by rods and arrows. Conserved residues are marked in red; those conserved in all enzymes (see Table 2, which is published as supporting information on the PNAS web site) are marked by asterisks, and metal ion ligands are marked by yellow circles.