Figure 3.
Fig. 3. (Left) View of CA26, molecule A. Those parts of
the molecule located at the front are light gray, those at the
back dark; glucose residues G are numbered 1-26. Curved arrows
indicate the "directions" of the two V-helices. The location of
the pseudo-twofold rotation axis ( ) is
between water molecules W1 and W2 and vertical to the plane of
the paper. Disordered water molecules filling the channel-like
cavities in the two V-helical segments are shown in red, as are
two five-coordinated water molecules, W1 and W2, in strategic
positions conferring stability to the folding of CA26. They are
hydrogen bonded in bidentate mode to O5/O6 atoms; W1 to G21 and
G2; W2 to G8 and G15, with additional single hydrogen bonds
W1···O(2)[8] and
W2···O(2)[21]. Water molecules W3 and W4
are not shown, as they are at the "back" of the molecule and
nearly overlap with W1 and W2. (Right) View as in Left, but
rotated 90° so that the pseudo-twofold axis (blue arrow) is
now horizontal. Shown is the interface between the two V-helices
where the band-flip segments, glucoses G26-G1 and G13-G14, are
connected by direct and water (W3 and W4)-mediated hydrogen
bonds to glucoses G7 and G20. Note superposition of G7 on G20,
forming part of the interface between the V-helices. Oxygen
atoms of glucose 1 are labeled. Drawn with INSIGHT II (32).
) is
between water molecules W1 and W2 and vertical to the plane of
the paper. Disordered water molecules filling the channel-like
cavities in the two V-helical segments are shown in red, as are
two five-coordinated water molecules, W1 and W2, in strategic
positions conferring stability to the folding of CA26. They are
hydrogen bonded in bidentate mode to O5/O6 atoms; W1 to G21 and
G2; W2 to G8 and G15, with additional single hydrogen bonds
W1···O(2)[8] and
W2···O(2)[21]. Water molecules W3 and W4
are not shown, as they are at the "back" of the molecule and
nearly overlap with W1 and W2. (Right) View as in Left, but
rotated 90° so that the pseudo-twofold axis (blue arrow) is
now horizontal. Shown is the interface between the two V-helices
where the band-flip segments, glucoses G26-G1 and G13-G14, are
connected by direct and water (W3 and W4)-mediated hydrogen
bonds to glucoses G7 and G20. Note superposition of G7 on G20,
forming part of the interface between the V-helices. Oxygen
atoms of glucose 1 are labeled. Drawn with INSIGHT II (32).