Distinct structural and functional properties of the ATPase sites in an asymmetric ABC transporter.
The ABC transporter associated with antigen processing (TAP) shuttles cytosolic peptides into the endoplasmic reticulum for loading onto class I MHC molecules. Transport is fueled by ATP binding and hydrolysis at two distinct cytosolic ATPase sites. One site comprises consensus motifs shared among most ABC transporters, while the second has substituted, degenerate motifs. Biochemical and crystallography experiments with a TAP cytosolic domain demonstrate that the consensus ATPase site has high catalytic activity and facilitates ATP-dependent dimerization of the cytosolic domains, which is an important conformational change during transport. In contrast, the degenerate site is defective in dimerization and ATP hydrolysis. Full-length TAP mutagenesis demonstrates the necessity for at least one consensus site, supporting our conclusion that the consensus site is the principal facilitator of substrate transport. Since asymmetry of the ATPase site motifs is a feature of many mammalian homologs, our proposed model has broad implications for ABC transporters.
Procko
Erik
E
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Ferrin-O'Connell
Ian
I
Ng
Sze-Ling
SL
Gaudet
Rachelle
R
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D016384:Consensus Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D006868:Hydrolysis; D008954:Models, Biological; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D051381:Rats
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; C486172:Tap1 protein, rat; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases