title: Structural and functional analysis of the TAP-inhibiting UL49.5 proteins of varicelloviruses.
abstract: Viral infections are counteracted by virus-specific cytotoxic T cells that recognize the infected cell via MHC class I (MHC I) molecules presenting virus-derived peptides. The loading of the peptides onto MHC I molecules occurs in the endoplasmic reticulum (ER) and is facilitated by the peptide loading complex. A key player in this complex is the transporter associated with antigen processing (TAP), which translocates the viral peptides from the cytosol into the ER. Herpesviruses have developed many strategies to evade cytotoxic T cells. Several members of the genus Varicellovirus encode a UL49.5 protein that prevents peptide transport through TAP. These include bovine herpesvirus (BoHV) 1, BoHV-5, bubaline herpesvirus 1, cervid herpesvirus 1, pseudorabies virus, felid herpesvirus 1, and equine herpesvirus 1 and 4. BoHV-1 UL49.5 inhibits TAP by preventing conformational changes essential for peptide transport and by inducing degradation of the TAP complex. UL49.5 consists of an ER luminal N-terminal domain, a transmembrane domain and a cytosolic C-terminal tail domain. In this study, the following features of UL49.5 were deciphered: (1) chimeric constructs of BoHV-1 and VZV UL49.5 attribute the lack of TAP inhibition by VZV UL49.5 to its ER-luminal domain, (2) the ER-luminal and TM domains of UL49.5 are required for efficient interaction with and inhibition of TAP, (3) the C-terminal RXRX sequence is essential for TAP degradation by BoHV-1 UL49.5, and (4) in addition to the RXRX sequence, the cytoplasmic tail of BoHV-1 UL49.5 carries a motif that is required for efficient TAP inhibition by the protein. A model is presented depicting how the different domains of UL49.5 may block the translocation of peptides by TAP and target TAP for proteasomal degradation.
authors.affiliation: Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Marieke C
authors.initials: MC
authors.lastname: Verweij
authors.forename: Andrea D
authors.initials: AD
authors.lastname: Lipińska
authors.forename: Danijela
authors.initials: D
authors.lastname: Koppers-Lalic
authors.forename: Edwin
authors.initials: E
authors.lastname: Quinten
authors.forename: Jessica
authors.initials: J
authors.lastname: Funke
authors.forename: Hans C
authors.initials: HC
authors.lastname: van Leeuwen
authors.forename: Krystyna
authors.initials: K
authors.lastname: Bieńkowska-Szewczyk
authors.forename: Joachim
authors.initials: J
authors.lastname: Koch
authors.forename: Maaike E
authors.initials: ME
authors.lastname: Ressing
authors.forename: Emmanuel J H J
authors.initials: EJ
authors.lastname: Wiertz
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D002469:Cell Separation; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D016133:Polymerase Chain Reaction; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology; D018140:Varicellovirus / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; C099455:UL49.5 protein, bovine herpesvirus type 1; D014759:Viral Envelope Proteins; C477327:transporter associated with antigen processing (TAP)