Figure 1.

Structure and sequence motifs of the founding member of the UlaG protein family, E. coli L-ascorbate 6-phosphate lactonase. A. Primary sequence of UlaG decorated with structural (from the Mn²⁺-loaded crystal structure, PDB 2wym) and functional annotations. Sequence segments not visible in the experimental electron density are shaded in gray. Secondary structure elements are shown as background colors, red (α-helices) and green (β-strands), and labeled from α1-α14 and βA-βN. Residues that form part of interaction surfaces are in bold and underlined. Finally, residues that directly (or indirectly) contribute to the Mn²⁺-binding site are marked with a star on a yellow background. B. Monomer structure of UlaG determined by X-ray crystallography at 2.6-Å resolution (PDB 2wym). Dashed lines represent missing loops in electron density (residues shaded in gray in A). C. Surface representation of the monomer where the interfacing residues are shown in light orange and are mapped onto the surface. D. Mn²⁺-binding site of UlaG. Side chains of residues from the coordination sphere are shown as sticks in atom colors and liganded Mn²⁺ ion in violet. E. Hexameric arrangement characteristic of the biologically active UlaG enzyme viewed along the threefold molecular symmetry axis.