Model for the Interaction of Gammaherpesvirus 68 RING-CH Finger Protein mK3 with Major Histocompatibility Complex Class I and the Peptide-Loading Complex

• DOI: 10.1128/jvi.78.16.8673-8686.2004
• Publication Date: 2004-07-27T18:42:49Z
• Authors: Xiaoli Wang; Lonnie Lybarger; Rose Connors; Michael R. Harris; Ted H. Hansen
• Keywords: Models, Molecular; Membrane Glycoproteins; Recombinant Fusion Proteins; Histocompatibility Antigens Class I; Molecular Sequence Data; Down-Regulation; Immunoglobulins; Membrane Transport Proteins; Antiporters; Substrate Specificity; 3. Good health; Mice; 03 medical and health sciences; Gammaherpesvirinae; 0302 clinical medicine; Antigens, CD; Herpesvirus 8, Human; Animals; Humans; ATP-Binding Cassette Transporters; Amino Acid Sequence; B7-2 Antigen; ATP Binding Cassette Transporter, Subfamily B, Member 2

ABSTRACTThe 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.