title: Viral inhibition of the transporter associated with antigen processing (TAP): a striking example of functional convergent evolution.
abstract: Herpesviruses are large DNA viruses that are highly abundant within their host populations. Even in the presence of a healthy immune system, these viruses manage to cause lifelong infections. This persistence is partially mediated by the virus entering latency, a phase of infection characterized by limited viral protein expression. Moreover, herpesviruses have devoted a significant part of their coding capacity to immune evasion strategies. It is believed that the close coexistence of herpesviruses and their hosts has resulted in the evolution of viral proteins that specifically attack multiple arms of the host immune system. Cytotoxic T lymphocytes (CTLs) play an important role in antiviral immunity. CTLs recognize their target through viral peptides presented in the context of MHC molecules at the cell surface. Every herpesvirus studied to date encodes multiple immune evasion molecules that effectively interfere with specific steps of the MHC class I antigen presentation pathway. The transporter associated with antigen processing (TAP) plays a key role in the loading of viral peptides onto MHC class I molecules. This is reflected by the numerous ways herpesviruses have developed to block TAP function. In this review, we describe the characteristics and mechanisms of action of all known virus-encoded TAP inhibitors. Orthologs of these proteins encoded by related viruses are identified, and the conservation of TAP inhibition is discussed. A phylogenetic analysis of members of the family Herpesviridae is included to study the origin of these molecules. In addition, we discuss the characteristics of the first TAP inhibitor identified outside the herpesvirus family, namely, in cowpox virus. The strategies of TAP inhibition employed by viruses are very distinct and are likely to have been acquired independently during evolution. These findings and the recent discovery of a non-herpesvirus TAP inhibitor represent a striking example of functional convergent evolution.
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Marieke C
authors.initials: MC
authors.lastname: Verweij
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Daniëlle
authors.initials: D
authors.lastname: Horst
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Griffin
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Rutger D
authors.initials: RD
authors.lastname: Luteijn
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Davison
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Maaike E
authors.initials: ME
authors.lastname: Ressing
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Emmanuel J H J
authors.initials: EJ
authors.lastname: Wiertz
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000276:immunology*; D000818:Animals; D005075:Biological Evolution; D006801:Humans; D057131:Immune Evasion / Q000235:genetics / Q000276:immunology*; D010802:Phylogeny; D014764:Viral Proteins / Q000276:immunology*; D014777:Virus Diseases / Q000235:genetics / Q000276:immunology*; D017735:Virus Latency / Q000276:immunology
chemical_list: D018528:ATP-Binding Cassette Transporters; D014764:Viral Proteins; C477327:transporter associated with antigen processing (TAP)