Crystal structures of the MJ1267 ATP binding cassette reveal an induced-fit effect at the ATPase active site of an ABC transporter.
BACKGROUND
ATP binding cassette (ABC) transporters are ubiquitously distributed transmembrane solute pumps that play a causative role in numerous diseases. Previous structures have defined the fold of the ABC and established the flexibility of its alpha-helical subdomain. But the nature of the mechanical changes that occur at each step of the chemical ATPase cycle have not been defined.


RESULTS
Crystal structures were determined of the MJ1267 ABC from Methanococcus jannaschii in Mg-ADP-bound and nucleotide-free forms. Comparison of these structures reveals an induced-fit effect at the active site likely to be a consequence of nucleotide binding. In the Mg-ADP-bound structure, the loop following the Walker B moves toward the Walker A (P-loop) coupled to backbone conformational changes in the intervening "H-loop", which contains an invariant histidine. These changes affect the region believed to mediate intercassette interaction in the ABC transporter complex. Comparison of the Mg-ADP-bound structure of MJ1267 to the ATP-bound structure of HisP suggests that an outward rotation of the alpha-helical subdomain is coupled to the loss of a molecular contact between the gamma-phosphate of ATP and an invariant glutamine in a segment connecting this subdomain to the core of the cassette.


CONCLUSIONS
The induced-fit effect and rotation of the alpha-helical subdomain may play a role in controlling the nucleotide-dependent change in cassette-cassette interaction affinity believed to represent the power-stroke of ABC transporters. Outward rotation of the alpha-helical subdomain also likely facilitates Mg-ADP release after hydrolysis. The MJ1267 structures therefore define features of the nucleotide-dependent conformational changes that drive transmembrane transport in ABC transporters.
Karpowich
N
N
Department of Biological Sciences, 702A Fairchild Center, MC2434, Columbia University, New York, NY 10027, USA.
Martsinkevich
O
O
Millen
L
L
Yuan
Y R
YR
Dai
P L
PL
MacVey
K
K
Thomas
P J
PJ
Hunt
J F
JF
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D026923:Amino Acid Transport Systems, Basic; D001426:Bacterial Proteins; D001665:Binding Sites; D020134:Catalytic Domain; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D008274:Magnesium / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism; D017017:Methanococcus / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010710:Phosphates / Q000378:metabolism; D010802:Phylogeny; D011487:Protein Conformation
D018528:ATP-Binding Cassette Transporters; D026923:Amino Acid Transport Systems, Basic; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D010710:Phosphates; C043828:histidine permease, Bacteria; D000255:Adenosine Triphosphate; D008274:Magnesium