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Mapping amino acids of the measles virus hemagglutinin responsible for receptor (CD46) downregulation.

We compared the amino acid sequences of groups of receptor (CD46) downregulating and nondownregulating measles virus (MV) hemagglutinins (Hs) and identified seven group-specific differences as candidates for the mediation of the observed differential effects. Using site-directed mutagenesis, we mutated the chosen amino acids of the H of MV-strain WTF (WTF-H), a nondownregulating H, and Introduced the corresponding amino acids of Edmonston-H (Edm-H), a downregulating H. We identified four amino acids, 211G, 243R, 451V, and 481Y, which influenced the downregulative function when introduced into WTF-H. The double mutation 451V and 481Y in WTF-H led to a degree of CD46 downregulation comparable to that of Edm-H. Conversely, introducing amino acids 451E and 481N into Edm-H resulted in a loss of the downregulative function. These results indicate that these amino acids play a decisive role in the H-CD46 interaction.