1. A Tweezers-like Motion of the ATP-Binding Cassette Dimer in an ABC Transport Cycle 
Jue Chen, Gang Lu, Jeffrey Lin, Amy L Davidson, Florante A Quiocho 
Molecular Cell 
Volume 12, Issue 3, Pages (September 2003)
DOI: /j.molcel

2. Figure 1
Ribbon Diagram of the Structure of E.c. MalK Homodimer with Bound ATP
(A) Subunit structure (molecule A in the asymmetric unit) with the nucleotide binding domain (NBD) (residues 1–235) in green/cyan color and regulatory domain (RD) (residues 236–370) in gray color. Different colors further distinguish the subdomains or segments in the NBD: green, RecA-like subdomain (residues 4–87 and 158–235); cyan, helical subdomain (residues 88–157); magenta, LSGGQ motif; red, Walker A motif. The ATP is represented in ball-and-stick model (O atom, red; N atom, blue; and P atom, yellow). NH2 and COOH identify the amino- and carboxyl-terminal ends, respectively.
(B) The homodimer, consisting of molecules A and B, viewed down the local 2-fold axis. The color schemes for the domains of the B molecule are similar to that of the A molecule shown in (A), except that they are rendered in lighter color.
(C) Stereoview of the homodimer obtained by a 90° clockwise rotation of the structure shown in (B) about a horizontal axis.
Molecular Cell  , DOI: ( /j.molcel )

3. Figure 2
Structure-Based Sequence Alignment of All ABC ATPases for Which the Dimeric Structures Have Been Published
E.c. MalK, T.l. MalK, MJ0796 E171Q mutant, and BtuD (Diederichs et al., 2000; Locher et al., 2002; Smith et al., 2002). Critical conserved sequence motifs (Walker A, Q loop, LSGGQ, Walker B, D loop and switch) (Gaudet and Wiley, 2001) are highlighted. Walker A and LSGGQ are colored according to Figure 1. Secondary structure elements are indicated above the sequence of E.c. MalK.
Molecular Cell  , DOI: ( /j.molcel )

4. Figure 3
ATP Binding
(A) Stereoview of the electron density (1.5 σ contour level) of one of the ATPs bound in the AB homodimer obtained from a simulated annealing Fo-Fc omit map. The refined ATP molecule was omitted in the structure factor calculation. Also shown are the residues from subunits A and B that are making contact with the ATP.
(B) Schematic diagram of the interaction between one of the two ATPs bound to the homodimer. Black lines represent van der Waals contacts, and blue lines correspond to hydrogen bonds and salt bridges. Color identification is as in Figure 1.
Molecular Cell  , DOI: ( /j.molcel )

5. Figure 4
Closed, Semi-Open, and Open Structures of MalK Homodimer with Superimposed RDs
The distances between two H89 residues in a homodimer are indicated.
(A) Superimposed closed form with bound ATP (yellow) and semi-open form without bound ATP (blue). The excellent overlap of the RDs is evident by the green color resulting from the combination of yellow and blue colors.
(B) Overlay of the semi-open (blue) and the open (red) nucleotide-free structures.
Molecular Cell  , DOI: ( /j.molcel )

6. Figure 5
A Model of the Interaction between the EAA Loops of MalF and MalG Transmembrane Proteins and the Q Loop of MalK
(A) Model of the docking of the L loop of BtuC to the Q loop of MalK. To obtain this model, the NBD of MalK from the ATP-bound structure was aligned with the NBD of BtuCD. Color codes: cyan, the BtuC L loop; blue, the Q loop of MalK; red and purple, the Walker A motif of one subunit and the LSGGQ motif of the other subunit, respectively. ATP is shown in ball-and-stick.
(B) Predicted helix-loop-helix motif of the EAA loops of MalF and MalG. The L loop in the crystal structure of BtuCD, which displays a helix-loop-helix configuration (Locher et al., 2002), is the equivalent of the EAA loops.
Molecular Cell  , DOI: ( /j.molcel )

7. Figure 6 A Model for Maltose Transport
In the ground state, the two NBDs of MalK are separated from each other, and a transmembrane translocation pathway is open to the cytoplasm. Maltose-loaded MBP binds to MalFGK2 and triggers major conformational changes that stimulate ATP hydrolysis and promote maltose transport across the membrane. In an intermediate state that is stabilized by the tight binding of MBP to the transporter, the NBDs have closed, permitting ATP hydrolysis to occur. MBP has opened in this intermediate, weakening the interaction between MBP and maltose and facilitating the transfer of sugar to the low-affinity binding site in MalFGK2. Opening of MBP and closing of the NBDs on opposite sides of the membrane could be tied to each other through a rocking motion in the transmembrane subunits that results in closure of maltose exit pathway into cytoplasm and opening of entrance into the membrane region at the periplasmic side. In the final stage, maltose is transported, and MBP is released after the reexposure of the internal binding site to the cytoplasm. MalFGK2 releases ADP and resets into the ground state. Modified from Chen et al. (2001).
Molecular Cell  , DOI: ( /j.molcel )