The contributions of glycosylation and GPI-linkage of the murine cytomegalovirus immune evasin, m157, to functional interactions with its lectin-like Ly49 receptors (128.25)

The MCMV-encoded glycoprotein, m157, is recognized by the activating Ly49HC57Bl/6 and inhibitory Ly49I129S lectin-like NK cell receptors. We and others have shown that Ly49H is tolerant to multiple amino acid changes in m157 with the exception of K161, which is predicted to anchor a unique N-terminal α0-helix to the main m157 chain. We undertook site-directed mutagenesis to address the contributions of N-linked glycosylation and the GPI anchor of m157 to Ly49H and Ly49I recognition. Variants of m157 containing single or multiple N-to-Q substitutions at positions N178, N187, N213, and N267, or fusions between the m157 extracellular domain and the transmembrane + cytoplasmic domains of DAP12 or CD4, were expressed in myeloid or fibroblast cell lines. We find that 1) only fully deglycosylated m157 has reduced capacity to activate Ly49H or chimeric Ly49HI reporter cells; 2) m157-CD4 transmembrane versions of m157 fully activate Ly49H and chimeric Ly49HI reporter lines; and 3) Ly49H+ NK cells are activated by all N-glycosylation and transmembrane variants of m157. Thus, neither N-glycosylation nor GPI anchoring of m157 is required for functional trans interactions with lectin-like Ly49 receptors.