Figure 3.
Figure 3. Difference in magnesium ion hydration in monomers A
and B. The 2Fo-Fc electron density maps of the hydrated
magnesium ions in the active sites of monomers A and B are
shown, contoured at 1.0 .
In monomer A, each of the coordinating water molecules is
clearly defined. In contrast, although three coordinating waters
are well defined in monomer B, and the temperature factors of
the magnesium ions and coordinating waters are similar, no
coordinating water at position 1 (asterisk) is visible in the
electron density map. As this position is the site of
interaction with the -phosphate
oxygen of bound GTP, facile exchange may be functionally
significant. The magnesium omit difference map allowed for an
identical interpretation. Thr112 and the phosphate groups of the
bound GDP are shown in each figure. The map cover radius was 1.1
Å, including the missing water position.
The above figure is reprinted
by permission from John Wiley & Sons, Inc.:
Proteins
(2004,
54,
222-230)
copyright 2004.
.
In monomer A, each of the coordinating water molecules is
clearly defined. In contrast, although three coordinating waters
are well defined in monomer B, and the temperature factors of
the magnesium ions and coordinating waters are similar, no
coordinating water at position 1 (asterisk) is visible in the
electron density map. As this position is the site of
interaction with the 
-phosphate
oxygen of bound GTP, facile exchange may be functionally
significant. The magnesium omit difference map allowed for an
identical interpretation. Thr112 and the phosphate groups of the
bound GDP are shown in each figure. The map cover radius was 1.1
Å, including the missing water position.