Functional role of C-terminal sequence elements in the transporter associated with antigen processing.
TAP delivers antigenic peptides into the endoplasmic reticulum (ER) that are subsequently bound by MHC class I molecules. TAP consists of two subunits (TAP1 and TAP2), each with a transmembrane (TMD) and a nucleotide-binding (NBD) domain. The two TAP-NBDs have distinct biochemical properties and control different steps during the peptide translocation process. We noted previously that the nonhomologous C-terminal tails of rat TAP1 and TAP2 determine the distinct functions of TAP-NBD1 and -NBD2. To identify the sequence elements responsible for the asymmetrical NBD function, we constructed chimeric rat TAP variants in which we systematically exchanged sequence regions of different length between the two TAP-NBDs. Our fine-mapping studies demonstrate that a nonhomologous region containing the alpha6/beta10-loop in conjunction with the downstream switch region is directly responsible for the functional separation of the TAP-NBDs. The alpha6/beta10-loop determines the nonsynonymous nucleotide binding of NBD1 and NBD2, whereas the switch region seems to play a critical role in regulating the functional cross-talk between the structural domains of TAP. Based on our findings, we postulate that these two sequence elements build a minimal functional unit that controls the asymmetry of the two TAP-NBDs.
Ehses
Sarah
S
Institute for Genetics, University of Cologne, Zülpicher Strasse 47, 50674 Cologne, Germany.
Leonhardt
Ralf M
RM
Hansen
Guido
G
Knittler
Michael R
MR
D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002678:Chimera; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology*; D051381:Rats
D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; C477327:transporter associated with antigen processing (TAP)