The human cytomegalovirus gene product US6 inhibits ATP binding by TAP

• Published in: The EMBO journal 2001-02, Vol.20 (3), p.387-396
• Main Authors: Hewitt, Eric W., Gupta, Soma Sen, Lehner, Paul J.
• Format: Article
• Language: English
• Subjects: ABC transporter; Adenosine Triphosphate - metabolism; Affinity Labels; Antigen Presentation; ATP; ATP Binding Cassette Transporter, Subfamily B, Member 2; ATP Binding Cassette Transporter, Subfamily B, Member 3; ATP-Binding Cassette Transporters - chemistry; ATP-Binding Cassette Transporters - metabolism; ATP-binding protein; Base Sequence; Binding Sites; Cell Line; Cytomegalovirus; Cytomegalovirus - genetics; Cytomegalovirus - immunology; Cytomegalovirus - metabolism; Drug Stability; HeLa Cells; Histocompatibility Antigens Class I - metabolism; Human cytomegalovirus; Humans; In Vitro Techniques; Oligonucleotide Probes - genetics; Peptides; Protein Conformation; TAP; TAP protein; TAP1 protein; Translocation; US6; US6 protein; Viral Envelope Proteins - genetics; Viral Envelope Proteins - immunology; Viral Envelope Proteins - metabolism
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/20.3.387

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°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.