title: Conserved amino acids within the adenovirus 2 E3/19K protein differentially affect downregulation of MHC class I and MICA/B proteins.
abstract: Successful establishment and persistence of adenovirus (Ad) infections are facilitated by immunosubversive functions encoded in the early transcription unit 3 (E3). The E3/19K protein has a dual role, preventing cell surface transport of MHC class I/HLA class I (MHC-I/HLA-I) Ags and the MHC-I-like molecules (MHC-I chain-related chain A and B [MICA/B]), thereby inhibiting both recognition by CD8 T cells and NK cells. Although some crucial functional elements in E3/19K have been identified, a systematic analysis of the functional importance of individual amino acids is missing. We now have substituted alanine for each of 21 aas in the luminal domain of Ad2 E3/19K conserved among Ads and investigated the effects on HLA-I downregulation by coimmunoprecipitation, pulse-chase analysis, and/or flow cytometry. Potential structural alterations were monitored using conformation-dependent E3/19K-specific mAbs. The results revealed that only a small number of mutations abrogated HLA-I complex formation (e.g., substitutions W52, M87, and W96). Mutants M87 and W96 were particularly interesting as they exhibited only minimal structural changes suggesting that these amino acids make direct contacts with HLA-I. The considerable number of substitutions with little functional defects implied that E3/19K may have additional cellular target molecules. Indeed, when assessing MICA/B cell-surface expression we found that mutation of T14 and M82 selectively compromised MICA/B downregulation with essentially no effect on HLA-I modulation. In general, downregulation of HLA-I was more severely affected than that of MICA/B; for example, substitutions W52, M87, and W96 essentially abrogated HLA-I modulation while largely retaining the ability to sequester MICA/B. Thus, distinct conserved amino acids seem preferentially important for a particular functional activity of E3/19K.
authors: Department of Biological Sciences, University of Warwick, Coventry, United Kingdom.
authors: Martina
authors: M
authors: Sester
authors: Katja
authors: K
authors: Koebernick
authors: Douglas
authors: D
authors: Owen
authors: Minghui
authors: M
authors: Ao
authors: Yana
authors: Y
authors: Bromberg
authors: Ed
authors: E
authors: May
authors: Emily
authors: E
authors: Stock
authors: Lawrence
authors: L
authors: Andrews
authors: Veronika
authors: V
authors: Groh
authors: Thomas
authors: T
authors: Spies
authors: Alexander
authors: A
authors: Steinle
authors: Beatrice
authors: B
authors: Menz
authors: Hans-Gerhard
authors: HG
authors: Burgert
mesh_terms: D000257:Adenoviridae Infections / Q000235:genetics / Q000378:metabolism*; D017503:Adenovirus E3 Proteins / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D015536:Down-Regulation; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D014162:Transfection
chemical_list: D017503:Adenovirus E3 Proteins; D015395:Histocompatibility Antigens Class I; C099187:MHC class I-related chain A; C098080:MICB antigen