Use of Functional Polymorphisms To Elucidate the Peptide Binding Site of TAP Complexes.
TAP1/TAP2 complexes translocate peptides from the cytosol to the endoplasmic reticulum lumen to enable immune surveillance by CD8(+) T cells. Peptide transport is preceded by peptide binding to a cytosol-accessible surface of TAP1/TAP2 complexes, but the location of the TAP peptide-binding pocket remains unknown. Guided by the known contributions of polymorphic TAP variants to peptide selection, we combined homology modeling of TAP with experimental measurements to identify several TAP residues that interact with peptides. Models for peptide-TAP complexes were generated, which indicate bent conformation for peptides. The peptide binding site of TAP is located at the hydrophobic boundary of the cytosolic membrane leaflet, with striking parallels to the glutathione binding site of NaAtm1, a transporter that functions in bacterial heavy metal detoxification. These studies illustrate the conservation of the ligand recognition modes of bacterial and mammalians transporters involved in peptide-guided cellular surveillance.
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109; and.
Jie
J
Geng
Department of Medicinal Chemistry, College of Pharmacy, University of Michigan Medical School, Ann Arbor, MI 48109.
Irina D
ID
Pogozheva
Department of Medicinal Chemistry, College of Pharmacy, University of Michigan Medical School, Ann Arbor, MI 48109.
Henry I
HI
Mosberg
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109; and malinir@umich.edu.
Malini
M
Raghavan
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics*; D002645:Chickens; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008285:Major Histocompatibility Complex / Q000235:genetics; D026901:Membrane Transport Proteins / Q000235:genetics*; D008958:Models, Molecular; D011110:Polymorphism, Genetic; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000235:genetics; D051381:Rats; D061987:Sf9 Cells; D018411:Spodoptera
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D026901:Membrane Transport Proteins; C073119:TAP1 protein, human; C071692:TAP2 protein, human