Model for the interaction of gammaherpesvirus 68 RING-CH finger protein mK3 with major histocompatibility complex class I and the peptide-loading complex.
The mK3 protein of gammaherpesvirus 68 and the kK5 protein of Kaposi's sarcoma-associated herpesvirus are members of a family of structurally related viral immune evasion molecules that all possess a RING-CH domain with ubiquitin ligase activity. These proteins modulate the expression of major histocompatibility complex class I molecules (mK3 and kK5) as well as other molecules like ICAM-1 and B7.2 (kK5). Previously, mK3 was shown to ubiquitinate nascent class I molecules, resulting in their rapid degradation, and this process was found to be dependent on TAP and tapasin, endoplasmic reticulum molecules involved in class I assembly. Here, we demonstrate that in murine cells, kK5 does not affect class I expression but does downregulate human B7.2 molecules in a TAP/tapasin-independent manner. These differences in substrate specificity and TAP/tapasin dependence between mK3 and kK5 permitted us, using chimeric molecules, to map the sites of mK3 interaction with TAP/tapasin and to determine the requirements for substrate recognition by mK3. Our findings indicate that mK3 interacts with TAP1 and -2 via their C-terminal domains and with class I molecules via their N-terminal domains. Furthermore, by orienting the RING-CH domain of mK3 appropriately with respect to class I, mK3 binding to TAP/tapasin, rather than the presence of unique sequences in class I, appears to be the primary determinant of substrate specificity.
Department of Pathology and Immunology, Box 8118, Washington University School of Medicine, 4566 Scott Ave., St. Louis, MO 63110, USA.
Xiaoli
X
Wang
Lonnie
L
Lybarger
Rose
R
Connors
Michael R
MR
Harris
Ted H
TH
Hansen
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D017920:Antiporters / Q000378:metabolism*; D051940:B7-2 Antigen; D015536:Down-Regulation; D018142:Gammaherpesvirinae / Q000378:metabolism* / Q000472:pathogenicity; D019288:Herpesvirus 8, Human / Q000378:metabolism / Q000472:pathogenicity; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013379:Substrate Specificity; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D015703:Antigens, CD; D017920:Antiporters; D051940:B7-2 Antigen; C497964:CD86 protein, human; C497965:Cd86 protein, mouse; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; D014764:Viral Proteins; C107762:tapasin; D044767:Ubiquitin-Protein Ligases