The human cytomegalovirus gene product US6 inhibits ATP binding by TAP.
Human cytomegalovirus (HCMV) encodes several genes that disrupt the major histocompatibility complex (MHC) class I antigen presentation pathway. We recently described the HCMV-encoded US6 gene product, a 23 kDa endoplasmic reticulum (ER)-resident type I integral membrane protein that binds to the transporter associated with antigen processing (TAP), inhibits peptide translocation and prevents MHC class I assembly. The functional consequence of this inhibition is to prevent the cell surface expression of class I bound viral peptides and their recognition by HCMV-specific cytotoxic T cells. Here we describe a novel mechanism of action for US6. We demonstrate that US6 inhibits the binding of ATP by TAP1. This is a conformational effect, as the ER lumenal domain of US6 is sufficient to inhibit ATP binding by the cytosolic nucleotide binding domain of TAP1. US6 also stabilizes TAP at 37 degrees C and prevents conformational rearrangements induced by peptide binding. Our findings suggest that the association of US6 with TAP stabilizes a conformation in TAP1 that prevents ATP binding and subsequent peptide translocation.
Hewitt
E W
EW
Division of Immunology, Department of Pathology, Wellcome Trust Centre for Molecular Mechanisms in Disease, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, UK.
Gupta
S S
SS
Lehner
P J
PJ
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000345:Affinity Labels; D017951:Antigen Presentation; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D003587:Cytomegalovirus / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004355:Drug Stability; D006367:HeLa Cells; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D015345:Oligonucleotide Probes / Q000235:genetics; D011487:Protein Conformation; D014759:Viral Envelope Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D000345:Affinity Labels; D015395:Histocompatibility Antigens Class I; D015345:Oligonucleotide Probes; C073119:TAP1 protein, human; D014759:Viral Envelope Proteins; C039447:glycoprotein D, Human herpesvirus 1; C071692:TAP2 protein, human; D000255:Adenosine Triphosphate