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Figure 2.
Figure 2. Crystal Structure of the MJ0796-E171Q ATP
Sandwich DimerThe stereo ribbon diagrams (Kraulis 1991 and
Merritt and Bacon 1997) are color coded according to subdomain
organization, with the F1-type ATP binding core shown in orange,
the antiparallel β subdomain in green, the α-helical subdomain
in blue, and the γ-phosphate linker in red. This color scheme
is equivalent to that used by Yuan et al. (2001), except for the
presentation of the γ-phosphate linker in red. See Figure 3B
for the location of the subdomains in the primary structure of
the protein.(A) Overall dimer structure. The bound Na-ATP
molecules are shown in space-filling representations, with the
nucleotides shown in magenta and the cation cofactors shown in
yellow. Sidechains contacting either the nucleotides or the
other subunit are shown in ball-and-stick representations,
color-coded according to the subdomain of origin; see Figure 3A
for a detailed contact diagram including the identity of all of
these residues. As shown here, the proximal face of the ABC
contacts the TM domains in the crystal structure of MsbA (Chang
and Roth, 2001).(B) Active site stereochemistry. Lighter shades
are used to indicate segments coming from the “A” subunit
whose Walker A motif is interacting with the nucleotide, while
darker shades are used to indicate segments coming from the
“B” subunit whose LSGGQ signature motif is interacting with
the nucleotide. The dotted lines indicate H bonds and are
colored to correspond to the donor group participating in the
interaction. The yellow sphere indicates the Na^+ cofactor of
the nucleotide. The turquoise spheres indicate water molecules,
with the rightmost one being the putative hydrolytic water.
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