Figure 4.
FIGURE 4. Conservation of active site structure and
mechanism. A, currently available structures of -carbonic
anhydrases can be divided into two groups: those in which the
conserved aspartate and arginine residues are hydrogen-bonded to
each other (CsoSCA, P. sativum, M. thermoautotrophicum, and
Rv1284) and those in which the hydrogen bonds are broken (P.
purpureum, E. coli, and Rv3588c). These are represented in dark
gray and light gray, respectively. In the former group, a water
molecule serves as the fourth ligand to the zinc ion. In the
latter group, the aspartate plays this role. The duality of
conformations suggests a conformational flexibility that might
play a role in catalysis. Residue numbering corresponds to
CsoSCA. B, a stereo figure showing a superpositioning of CsoSCA
(light gray) and P. sativum (dark gray) enzymes. A ion
was modeled into the active site, based on similarities with the
position of the acetate ion found in the P. sativum structure.
Small changes in orientation of the allowed
hydrogen bonds to form between the and
zinc, His-397, Asp-175, and backbone nitrogens of Ala-254 and
Ala-255.
The above figure is reprinted
by permission from the ASBMB:
J Biol Chem
(2006,
281,
7546-7555)
copyright 2006.
-carbonic
anhydrases can be divided into two groups: those in which the
conserved aspartate and arginine residues are hydrogen-bonded to
each other (CsoSCA, P. sativum, M. thermoautotrophicum, and
Rv1284) and those in which the hydrogen bonds are broken (P.
purpureum, E. coli, and Rv3588c). These are represented in dark
gray and light gray, respectively. In the former group, a water
molecule serves as the fourth ligand to the zinc ion. In the
latter group, the aspartate plays this role. The duality of
conformations suggests a conformational flexibility that might
play a role in catalysis. Residue numbering corresponds to
CsoSCA. B, a stereo figure showing a superpositioning of CsoSCA
(light gray) and P. sativum (dark gray) enzymes. A 
ion
was modeled into the active site, based on similarities with the
position of the acetate ion found in the P. sativum structure.
Small changes in orientation of the