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Mapping of the primary binding site of measles virus to its receptor CD46
C J Buchholz1, D Koller, P Devaux
1Institut für Molekularbiologie, Abt.I, Universität Zürich, Hönggerberg, CH-8093 Zürich, Switzerland. cb2@mrc-lmb.cam.ac.uk
Abstract:
The measles virus (MV) hemagglutinin binds to the complement control protein (CCP) CD46 primarily through the two external modules, CCP-I and -II. To define the residues involved in binding, 40 amino acids predicted to be solvent-exposed on the CCP-I-II module surface were changed to either alanine or serine. Altered proteins were expressed on the cell surface, and their abilities to bind purified MV particles, a soluble form of hemagglutinin (sH) and nine CD46-specific antibodies competing to different levels with sH attachment, were measured. All proteins retained, at least in part, MV and sH binding, but some completely lost binding to certain antibodies. Amino acids essential for binding of antibodies weakly or moderately competing with sH attachment are situated in the membrane-distal tip of CCP-I, whereas residues involved in binding of strongly sH competing antibodies cluster in the center of CCP-I (Arg-25, Asp-27) or in CCP-II (Arg-69, Asp-70). Both clusters face the same side of CCP-I-II and map close to amino acid exchanges impairing sH binding (E11A, R29A, P39A, and D70A) or MV binding (D70A and E84A) and to a six-amino acid loop, previously shown to be necessary for sH binding.
Insights
Researchers identified key amino acid residues on the measles virus (MV) hemagglutinin protein responsible for binding to complement control protein (CCP) CD46. These findings are crucial for understanding MV entry and developing antiviral strategies.
Area of Science:
- Virology
- Immunology
- Structural Biology
Background:
- Measles virus (MV) hemagglutinin (H) mediates viral entry by binding to host cell receptors.
- Complement control protein (CCP) CD46 is a primary receptor for MV, interacting mainly through its external CCP-I and -II modules.
- Understanding the precise binding interface is essential for developing targeted antiviral therapies.
Purpose of the Study:
- To identify specific amino acid residues on the CCP-I-II module of CD46 critical for MV hemagglutinin binding.
- To elucidate the roles of these residues in mediating interactions with MV particles, soluble hemagglutinin (sH), and CD46-specific antibodies.
Main Methods:
- Site-directed mutagenesis was used to alter 40 solvent-exposed amino acids on the CD46 CCP-I-II module to alanine or serine.
- Mutated CD46 proteins were expressed on the cell surface and assessed for binding to purified MV, sH, and nine competing antibodies.
- Binding affinities were quantified to determine the impact of amino acid substitutions on protein-protein interactions.
Main Results:
- All CD46 mutants retained partial binding to MV and sH, indicating the robustness of the interaction.
- Specific mutations in CCP-I (membrane-distal tip) affected binding to weakly or moderately competing antibodies.
- Mutations in the center of CCP-I (Arg-25, Asp-27) and CCP-II (Arg-69, Asp-70) impaired binding to strongly competing antibodies and, in some cases, MV/sH binding.
- Identified residues cluster on the same face of CCP-I-II, near previously identified critical regions for sH binding.
Conclusions:
- Specific amino acid clusters on CD46 CCP-I and CCP-II are critical for high-affinity binding of MV hemagglutinin.
- Residues in CCP-I are differentially involved in binding antibodies that compete with sH attachment.
- These findings provide a detailed molecular map of the MV-CD46 interaction, aiding in the design of entry inhibitors.