TRANSFER OF AN ESTERASE-RESISTANT RECEPTOR ANALOG TO THE SURFACE OF INFLUENZA-C VIRIONS RESULTS IN REDUCED INFECTIVITY DUE TO AGGREGATE FORMATION

A synthetic sialic acid, N-acetyl-9-thioacetamidoneuraminic acid (9-Th ioAcNeu5Ac), is recognized by influenza C virus as a receptor determin ant but - in contrast to the natural receptor determinant, N-acetyl-9- O-acetylneuraminic acid - is resistant to inactivation by the viral ac etylesterase. This sialic acid analog was used to analyze the importan ce of the receptor-destroying enzyme of influenza C virus in keeping t he viral surface free of receptor determinants. Enzymatic transfer of 9-ThioAcNeu5Ac to the surface of influenza C virions resulted in the l oss of the hemagglutinating activity. The ability to agglutinate eryth rocytes was restored when the synthetic sialic acid was released from the viral surface by neuraminidase treatment. Infectivity of influenza C virus containing surface-bound 9-ThioAcNeu5Ac was reduced about 20- fold. Sedimentation analysis as well as electron microscopy indicated that virions resialylated with the esterase-resistant sialic acid anal og formed virus aggregates. These results indicate that the receptor-d estroying enzyme of influenza C virus is required to avoid the presenc e of receptor determinants on the virion surface and thus to prevent a ggregate formation and a reduction of the infectious titer. (C) 1996 A cademic Press, Inc.