PDBsum entry 1l2t

Transport protein

PDB id: 1l2t

Contents

Protein chains

230 a.a. *

Ligands

ATP ×2

IPA ×2

Metals

_NA ×2

Waters ×417

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Atp binding to the motor domain from an abc transporter drives formation of a nucleotide sandwich dimer.

Authors

P.C.Smith, N.Karpowich, L.Millen, J.E.Moody, J.Rosen, P.J.Thomas, J.F.Hunt.

Ref.

Mol Cell, 2002, 10, 139-149. [DOI no: 10.1016/S1097-2765(02)00576-2]

PubMed id

12150914

Abstract

It has been proposed that the reaction cycle of ATP binding cassette (ABC) transporters is driven by dimerization of their ABC motor domains upon binding ATP at their mutual interface. However, no such ATP sandwich complex has been observed for an ABC from an ABC transporter. In this paper, we report the crystal structure of a stable dimer formed by the E171Q mutant of the MJ0796 ABC, which is hydrolytically inactive due to mutation of the catalytic base. The structure shows a symmetrical dimer in which two ATP molecules are each sandwiched between the Walker A motif in one subunit and the LSGGQ signature motif in the other subunit. These results establish the stereochemical basis of the power stroke of ABC transporter pumps.

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.

Figure 4.
Figure 4. Conformational Differences between ADP-Bound and ATP-Bound MJ0796 MonomersThe crystal structure of Mg-ADP-bound wild-type MJ0796 (Yuan et al., 2001) (lighter colors) is superimposed on that of the Na-ATP-bound E171Q mutant (darker colors) based on least-squares alignment of 65 Cα atoms located in the α helix following the Walker A motif and the 6 β strands in the F1-type ATP binding core. The backbone and sidechains of each model are color coded according to subdomain organization as in Figure 2A. The crystal structure of the E171Q mutant of MJ0796 bound to Mg-ADP is essentially identical to that of the wild-type protein bound to the same ligand (data not shown). This view shows the molecular surface of the monomer facing the intersubunit interface in the nucleotide sandwich dimer.

The above figures are reprinted by permission from Cell Press: Mol Cell (2002, 10, 139-149) copyright 2002.