Figure 8 - full size

 

Figure 8.
Figure 8. (a) Stereo view of the active site of the ternary complex of EcoRV cocrystallized with cognate DNA and Ca 2+ . The position of the leaving 30 oxygen atom of the scissile bond is indicated. In this conformation, in-line attack of the hydroxide ion to form the expected trigonal bipyramid in the transition state must be from the face opposite the position of the carboxylate groups. The calcium ion (#283 CL) binds between Asp90, Asp74 and the scissile phos- phate groups. Helix B is at the left. (b) Detailed view of the ligation of the calcium ion in subunit I of the EcoRV- DNA-Ca 2+ complex, including distances (in Å ) as determined from the final refined coordinate set. The scissile phos- phate group is shown at the top. The ligation of Ca 2+ in subunit II is very similar, except that electron density for one apical water molecule is not apparent in electron density maps, and the two oxygen atoms of Asp90 are located in the equatorial plane at distances of 2.53 Å and 2.46 Å from the calcium ion.

The above figure is reprinted by permission from Elsevier: J Mol Biol (1997, 273, 207-225) copyright 1997.