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Figure 4.
Figure 4. (a) Superposition of the (2|F[o]|−|F[c]|),
α[c] map onto the refined structure of I222
streptavidin-biotin, pH 2.00, 1.36 Å resolution, showing
the binding site of biotin and its interaction with Trp120 of a
neighboring subunit. Residues hydrogen bonding to biotin are
labeled in yellow font. (b) Superposition of the
(2|F[o]|−|F[c]|), α[c] map onto the refined structure of I222
streptavidin-2-iminobiotin, pH 3.25, 1.39 Å resolution.
Residues hydrogen bonding to the ligand are labeled in yellow.
Tyr43 is discretely disordered between two well-defined
conformations involving a rotation of 5° in χ1. (c)
Superposition of the (2|F[o]|−|F[c]|), α[c] map onto the
refined structure of I222 streptavidin-glycoluril, pH 2.50, 1.40
Å resolution. Residues hydrogen bonding to the ligand are
labeled in yellow. Normal hydrogen bonds mediating ligand
binding are shown in yellow, and the NH → πTrp108 hydrogen
bond in white. Note that Leu110 is discretely disordered.
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