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.
Wang
Xiaoli
X
Department of Pathology and Immunology, Box 8118, Washington University School of Medicine, 4566 Scott Ave., St. Louis, MO 63110, USA.
Lybarger
Lonnie
L
Connors
Rose
R
Harris
Michael R
MR
Hansen
Ted H
TH
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