|
Figure 7.
FIG. 7. Stereo view of the Na^+ binding environment in the
structures of F (free fast form, gold), S (free slow form, red),
FL (PPACK-bound fast form, blue), and SL (PPACK-bound slow form,
green). Shown are all atoms within 3 Å of the bound Na^+
in the F structure, in addition to the side chains of Asp-189
and Asp-221. Note the similarity of the Na^+ coordination shell
between F and FL; the bound Na^+ is coordinated octahedrally by
the backbone O atoms of Lys-224 and Arg-221a and by four buried
water molecules that H-bond to (clockwise) Asp-189, Asp-221,
Gly-223, and Tyr-184a. Only some of these water molecules are
replaced in the absence of Na^+ (S and SL). Note the
rearrangement of the side chain of Asp-189 in the S structure
and the significant shift in the backbone O atom of Arg-221a
that assumes a position incompatible with Na^+ coordination.
H-bonds are shown by broken lines and refer to the F structure.
|
