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Figure 3.
Figure 3. Crystal Structures of Three TAP1-NBD Constructs
with ATP
(A) TAP1-NBD D→N·ATP is a dimer with two
ATP-Mg^2+ at the interface. The two NBDs, colored light and dark
blue, are viewed from the TMDs looking down onto the NBDs.
Important functional motifs are highlighted in one active site.
(B) NBDs from the three structures were superimposed via
their ATPase subdomains (lighter shades). This demonstrates
rigid-body motions of the helical subdomain (darker shades).
(C and D) σA-weighted 2F[o]–F[c] map, contoured at 1.3
σ, for the consensus (TAP1-NBD D→Q/Q→H) (C) and hybrid
(TAP1-NBD D→N) (D) active sites. The putative hydrolytic water
is labeled.
(E) The degenerate TAP1-NBD SG→AV/D→N
signature motif structure (magenta) superimposed onto the
consensus active site (green). Polar contacts from S621 of the
consensus signature motif are shown.
(F) Stereoview of the
superposition in (E), zooming in on the two residues that differ
between the consensus (green) and degenerate (magenta) signature
motifs. The van der Waals radii of V622 and a Mg^2+-coordinated
water are shown with a dotted surface, demonstrating a steric
clash.
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