Figure 3 - full size


Figure 3.
Fig. 3. Schematic drawing showing the CA XII dimer in the membrane; orientation is the same as that in Fig. 2. The extracellular CA domains (molecules A and B) are colored blue and green, respectively. Zinc ions appear as white spheres, disulfide linkages are yellow, and acetazolamide molecules appear as balls-and-sticks. The yellow transmembrane helices are modeled after the structure of the glycophorin A dimer reported by MacKenzie and colleagues (42): both CA XII and glycophorin A contain transmembrane GXXXG dimerization motifs (40, 41). The intracellular C-terminal domains appear as orange spheres. These domains contain potential phosphorylation sites but are currently of unknown structure. Note that membrane association orients the enzyme active sites toward the extracellular milieu, poised for catalysis.