FIGURE 3.

The modular structure of the secreted epimerases from Azotobacter vinelandii. The AlgE epimerases from A. vinelandii is composed of varying numbers of the two modules designated A and R. The relatedness between individual modules (confer Figure 4) is indicated by the similarity of the colors. The Ca²⁺-binding motifs found at the N-terminal end of each R-module are indicated by vertical lines. The proposed substrate-binding subsites in the A-module of AlgE4 are indicated by lines within the module, the catalytic subsite is marked with an asterisk.