Fig. 5. Stereoview of the P loop in FPGS (blue bonds)
overlaid with the P loop from p21-ras (red bonds). The location
of the pyrophosphate and the Mg2+ are given in black,
superimposed on F[o]-F[c] omit density for the PPi and the Mg2+.
The proposed location of the -phosphate
is the lobe of F[o]-F[c] density between the PPi and the
sidechain of Lys50. The conserved lysine residue in the P loop
is indicated for FPGS (Lys50, magenta) and p21-ras (Lys16,
orange), along with a conserved acidic residue adjacent to the
active site, which is Glu143 in FPGS and is Asp57 in p21-ras.
The first two residues of the loop
(Ser73 and Pro74) are indicated in cyan.