Braun, Werner

ABSTRACTSignaling lymphocytic activation molecule (SLAM, CD150) is the universal morbillivirus receptor. Based on the identification of measles virus (MV) hemagglutinin (H) amino acids supporting human SLAM-dependent cell entry, we mutated canine distemper virus (CDV) H and identified residues necessary for efficient canine SLAM-dependent membrane fusion. These residues are located in two nearby clusters in a new CDV H structural model. To completely abolish SLAM-dependent fusion, combinations of mutations were necessary. We rescued a SLAM-blind recombinant CDV with six mutations that did not infect ferret peripheral blood mononuclear cells while retaining full infectivity in epithelial cells.

ABSTRACTMeasles virus (MV) enters cells either through the signaling lymphocyte activation molecule SLAM (CD150) expressed only in immune cells or through the ubiquitously expressed regulator of complement activation, CD46. To identify residues on the attachment protein hemagglutinin (H) essential for fusion support through either receptor, we devised a strategy based on analysis of morbillivirus H-protein sequences, iterative cycles of mutant protein production followed by receptor-based functional assays, and a novel MV H three-dimensional model. This model uses the Newcastle disease virus hemagglutinin-neuraminidase protein structure as a template. We identified seven amino acids important for SLAM- and nine for CD46 (Vero cell receptor)-induced fusion. The MV H three-dimensional model suggests (i) that SLAM- and CD46-relevant residues are located in contiguous areas in propeller β-sheets 5 and 4, respectively; (ii) that two clusters of SLAM-relevant residues exist and that they are accessible for receptor contact; and (iii) that several CD46-relevant amino acids may be shielded from direct receptor contacts. It appears likely that certain residues support receptor-specific H-protein conformational changes. To verify the importance of the H residues identified with the cell-cell fusion assays for virus entry into cells, we transferred the relevant mutations into genomic MV cDNAs. Indeed, we were able to recover recombinant viruses, and we showed that these replicate selectively in cells expressing SLAM or CD46. Selectively receptor-blind viruses will be used to study MV pathogenesis and may have applications for the production of novel vaccines and therapeutics.