The varicellovirus UL49.5 protein blocks the transporter associated with antigen processing (TAP) by inhibiting essential conformational transitions in the 6+6 transmembrane TAP core complex.
TAP translocates virus-derived peptides from the cytosol into the endoplasmic reticulum, where the peptides are loaded onto MHC class I molecules. This process is crucial for the detection of virus-infected cells by CTL that recognize the MHC class I-peptide complexes at the cell surface. The varicellovirus bovine herpesvirus 1 encodes a protein, UL49.5, that acts as a potent inhibitor of TAP. UL49.5 acts in two ways, as follows: 1) by blocking conformational changes of TAP required for the translocation of peptides into the endoplasmic reticulum, and 2) by targeting TAP1 and TAP2 for proteasomal degradation. At present, it is unknown whether UL49.5 interacts with TAP1, TAP2, or both. The contribution of other members of the peptide-loading complex has not been established. Using TAP-deficient cells reconstituted with wild-type and recombinant forms of TAP1 and TAP2, TAP was defined as the prime target of UL49.5 within the peptide-loading complex. The presence of TAP1 and TAP2 was required for efficient interaction with UL49.5. Using deletion mutants of TAP1 and TAP2, the 6+6 transmembrane core complex of TAP was shown to be sufficient for UL49.5 to interact with TAP and block its function. However, UL49.5-induced inhibition of peptide transport was most efficient in cells expressing full-length TAP1 and TAP2. Inhibition of TAP by UL49.5 appeared to be independent of the presence of other peptide-loading complex components, including tapasin. These results demonstrate that UL49.5 acts directly on the 6+6 transmembrane TAP core complex of TAP by blocking essential conformational transitions required for peptide transport.
Verweij
Marieke C
MC
Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands.
Koppers-Lalic
Danijela
D
Loch
Sandra
S
Klauschies
Florian
F
de la Salle
Henri
H
Quinten
Edwin
E
Lehner
Paul J
PJ
Mulder
Arend
A
Knittler
Michael R
MR
Tampé
Robert
R
Koch
Joachim
J
Ressing
Maaike E
ME
Wiertz
Emmanuel J H J
EJ
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D019281:Dimerization; D007242:Herpesvirus 1, Bovine / Q000502:physiology*; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D014759:Viral Envelope Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010455:Peptides; C073119:TAP1 protein, human; C099455:UL49.5 protein, bovine herpesvirus type 1; D014759:Viral Envelope Proteins; C107762:tapasin; C477327:transporter associated with antigen processing (TAP); C071692:TAP2 protein, human