A 3D model for the measles virus receptor CD46 based on homology modeling, Monte Carlo simulations, and hemagglutinin binding studies

Abstract

The two terminal complement control protein (CCP) modules of the CD46 glycoprotein mediate measles virus binding. Three-dimensional models for these two domains were derived based on the NMR structures of two CCP modules of factor H. Both CD46 CCP modules are about 35 8, long, and form a five-stranded antiparallel P-barrel structure. Monte Carlo simulations, sampling the backbone torsion angles of the linker peptide and selecting possible orientations on the basis of minimal solvent-exposed hydrophobic area, were used to predict the orientation of CCP-I relative to CCP-11. We tested this procedure successfully for factor H. For CD46, three clusters of structures differing in the tilt angle of the two domains were obtained. To test these models, we mutagenized the CCP modules. Four proteins, two without an oligosaccharide chain and two with mutated short amino acid segments, reached the cell surface efficiently. Only the protein without the CCP-I oligosaccharide chain maintained binding to the viral attachment protein hemagglutinin. These results are consistent with one of our models and suggest that the viral hemagglutinin does not bind at the membrane-distal tip of CD46, but near the concave CCP-1-11 interface region.

Dissecting Sites Important for Complement Regulatory Activity in Membrane Cofactor Protein (MCP; CD46)

“…24)). This same region has been implicated in MV binding by multiple groups (24,25,27,36,37). Thus, these results point to a second site in MCP, encompassing amino acids 94 -103, important for both C4b and MV interactions.…”

Mapping of the Primary Binding Site of Measles Virus to Its Receptor CD46

“…Proteins-Mutagenesis studies in the CD46 CCP-I-II modules revealed that exchange of short peptide segments often resulted in loss of surface expression and in reduced reactivity to several CD46 mAbs, suggesting impaired protein folding (27). To minimize folding problems, we opted for a mutagenesis technique based on replacement of single amino acids by small residues (alanine for charged and polar, serine for apolar residues), thus likely allowing maintenance of the …”

“…We previously approached the definition of the primary MV binding site by H protein binding studies based on a threedimensional model of CCP-I-II (27). The three-dimensional model was based on the NMR structure of the CCP modules from another member of the RCA protein family, the human complement factor H. Each of the two CD46 modules is predicted to be about 35 Å long and to form a five-stranded ␤-barrel structure (27).…”

“…The three-dimensional model was based on the NMR structure of the CCP modules from another member of the RCA protein family, the human complement factor H. Each of the two CD46 modules is predicted to be about 35 Å long and to form a five-stranded ␤-barrel structure (27). The two modules are tilted.…”

“…We constructed proteins with intermodule exchanges of CCP-I and -II segments. Two of the few altered proteins that reached the cell surface efficiently, a six-amino acid CCP-I exchange mutant (P39-T44, the one letter amino acid code is used) and a 12-amino acid CCP-II exchange mutant (N94-L105), lost H protein binding (27). Partial (P39-T44) or total (N94-L105) loss of reactivity with conformation-depend-ent antibodies indicated that both mutant proteins did not maintain the native conformation of the CCP modules.…”