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Figure 2.
Figure 2. Trehalose (Glc-α(1 → 1)α-Glc) binding to
maltoporin and a comparison of its interactions with those
observed for sucrose. (a) Stereo view of the trehalose complex,
with the sugar moiety colored in light blue, while the residues
of the greasy slide and Tyr118 (right) are shown in atom
colors. The extracellular side of the barrel is at the top, the
periplasmic side at the bottom of the panel, with the channel
axis in the plane of the paper. The averaged F[obs]−F[calc]
vector difference map (see Materials and Methods) of the
maltoporin-trehalose complex is contoured at +4 σ and −4 σ
(green and red contours, respectively). Flat continuous density
is found for one glucosyl moiety. Most of the remaining positive
density peaks correspond to water molecules (red spheres) as
determined in the maltoporin-sucrose complex. The water
structure has not been used for the structure determination of
the trehalose complex. The (clipped) C^α-trace of a maltoporin
monomer is shown in yellow, and loop L#2, originating from
the adjacent subunit and contributing Trp#74, in blue. (b)
Superposition of the binding of trehalose (atom colors) and
sucrose (green) to maltoporin, as obtained by structural
alignment of the respective C^α-traces. The leading glucose
moiety in trehalose (bottom) and the glucosyl moiety of sucrose
exhibit essentially identical interactions with the protein. No
density has been found for the other glucosyl residue of
trehalose (a) which has been modeled based on stereochemical
restraints.
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