Canine Distemper Virus Fusion Activation: Critical Role of Residue E123 of CD150/SLAM

• Published in: Journal of virology 2016-02, Vol.90 (3), p.1622-1637
• Main Authors: Khosravi, Mojtaba, Bringolf, Fanny, Röthlisberger, Silvan, Bieringer, Maria, Schneider-Schaulies, Jürgen, Zurbriggen, Andreas, Origgi, Francesco, Plattet, Philippe
• Format: Article
• Language: English
• Subjects: Animals; Antigens, CD - genetics; Antigens, CD - metabolism; Binding Sites; Canine distemper virus; Cell Line; Distemper Virus, Canine - physiology; DNA Mutational Analysis; Host-Pathogen Interactions; Humans; Measles virus; Membrane Fusion Proteins - metabolism; Mutant Proteins - genetics; Mutant Proteins - metabolism; Protein Binding; Receptors, Cell Surface - genetics; Receptors, Cell Surface - metabolism; Signaling Lymphocytic Activation Molecule Family Member 1; Virus Internalization; Virus-Cell Interactions
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/jvi.02405-15

Measles virus (MeV) and canine distemper virus (CDV) possess tetrameric attachment proteins (H) and trimeric fusion proteins, which cooperate with either SLAM or nectin 4 receptors to trigger membrane fusion for cell entry. While the MeV H-SLAM cocrystal structure revealed the binding interface, two distinct oligomeric H assemblies were also determined. In one of the conformations, two SLAM units were sandwiched between two discrete H head domains, thus spotlighting two binding interfaces ("front" and "back"). Here, we investigated the functional relevance of both interfaces in activating the CDV membrane fusion machinery. While alanine-scanning mutagenesis identified five critical regulatory residues in the front H-binding site of SLAM, the replacement of a conserved glutamate residue (E at position 123, replaced with A [E123A]) led to the most pronounced impact on fusion promotion. Intriguingly, while determination of the interaction of H with the receptor using soluble constructs revealed reduced binding for the identified SLAM mutants, no effect was recorded when physical interaction was investigated with the full-length counterparts of both molecules. Conversely, although mutagenesis of three strategically selected residues within the back H-binding site of SLAM did not substantially affect fusion triggering, nevertheless, the mutants weakened the H-SLAM interaction recorded with the membrane-anchored protein constructs. Collectively, our findings support a mode of binding between the attachment protein and the V domain of SLAM that is common to all morbilliviruses and suggest a major role of the SLAM residue E123, located at the front H-binding site, in triggering the fusion machinery. However, our data additionally support the hypothesis that other microdomain(s) of both glycoproteins (including the back H-binding site) might be required to achieve fully productive H-SLAM interactions. A complete understanding of the measles virus and canine distemper virus (CDV) cell entry molecular framework is still lacking, thus impeding the rational design of antivirals. Both viruses share many biological features that partially rely on the use of analogous Ig-like host cell receptors, namely, SLAM and nectin 4, for entering immune and epithelial cells, respectively. Here, we provide evidence that the mode of binding between the membrane-distal V domain of SLAM and the attachment protein (H) of morbilliviruses is very likely conserved. Moreover, although struct