Human cytomegalovirus US2 endoplasmic reticulum-lumenal domain dictates association with major histocompatibility complex class I in a locus-specific manner.
The human cytomegalovirus-encoded US2 glycoprotein targets endoplasmic reticulum-resident major histocompatibility complex (MHC) class I heavy chains for rapid degradation by the proteasome. We demonstrate that the endoplasmic reticulum-lumenal domain of US2 allows tight interaction with class I molecules encoded by the HLA-A locus. Recombinant soluble US2 binds properly folded, peptide-containing recombinant HLA-A2 molecules in a peptide sequence-independent manner, consistent with US2's ability to broadly downregulate class I molecules. The physicochemical properties of the US2/MHC class I complex suggest a 1:1 stoichiometry. These results demonstrate that US2 does not require additional cellular proteins to specifically interact with soluble class I molecules. Binding of US2 does not significantly alter the conformation of class I molecules, as a soluble T-cell receptor can simultaneously recognize class I molecules associated with US2. The lumenal domain of US2 can differentiate between the products of distinct class I loci, as US2 binds several HLA-A locus products while being unable to bind recombinant HLA-B7, HLA-B27, HLA-Cw4, or HLA-E. We did not observe interaction between soluble US2 and either recombinant HLA-DR1 or recombinant HLA-DM. The substrate specificity of US2 may help explain the presence in human cytomegalovirus of multiple strategies for downregulation of MHC class I molecules.
Gewurz
B E
BE
Department of Pathology, , Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Wang
E W
EW
Tortorella
D
D
Schust
D J
DJ
Ploegh
H L
HL
D003587:Cytomegalovirus / Q000737:chemistry / Q000378:metabolism*; D015536:Down-Regulation; D004926:Escherichia coli; D015789:HLA-A2 Antigen / Q000096:biosynthesis / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000096:biosynthesis / Q000378:metabolism*
D015789:HLA-A2 Antigen; D015395:Histocompatibility Antigens Class I; D011994:Recombinant Proteins; C118670:US2 protein, Varicellovirus; D014759:Viral Envelope Proteins