Plays a role as antagonist of host tetherin (BST2), disrupting its antiviral effect. Acts by binding to BST2 thereby interfering with its glycosylation. May suppress small interfering RNA (siRNA). May bind to host ITGAL, thereby playing a role in attachment or modulation of leukocytes. Interacts with the spike glycoprotein (PubMed:16840309). Interacts with M protein (PubMed:16580632). Interacts with E protein (PubMed:16580632). Interacts with the ORF3a protein (PubMed:15194747). Interacts with human SGT (PubMed:16580632). Interacts with host ITGAL (PubMed:18020948). Interacts with host BST2 (PubMed:26378163). The di-lysine motif confers endoplasmic reticulum localization for type I membrane proteins.