The Spike Protein of Potato Yellow Dwarf Virus and Its Functional Role in the Infection of Insect Vector Cells

Summary Treatment of particles of potato yellow dwarf virus, serotype SYDV, with non-ionic detergents solubilized two of the five structural proteins, G and M1. Since only these proteins were also recovered in lipid vesicles prepared either by a detergent dialysis technique or after organic extraction of purified virus using phosphatidylcholine in n-hexane, it is suggested that M2 protein is not membrane-associated but rather belongs to the core. The SYDV spike protein G was purified by isoelectric focusing during which it appeared to be heterogeneous in charge with most of the protein banding at pH 4.8. The same heterogeneity was observed after two-dimensional protein gel electrophoresis, where SYDV G protein was found largely at pH 4.8, whereas that of the other PYDV serotype, CYDV, was detected largely at pH 4.3. Antibodies raised against purified SYDV G protein reacted specifically with the G protein. When they were present during the inoculation step, G-specific antibodies were able to neutralize the infectivity of SYDV for insect vector cell monolayers, which suggests that G protein has a functional role in the inoculation process. Isolated SYDV G protein or SYDV envelope vesicles containing G protein inhibited the infection of vector cells by SYDV; however, only with SYDV envelope vesicles was the inhibition concentration-dependent. This indicated competition between virions and the vesicles during the inoculation process, possibly for recognition or attachment sites.