Interaction of rotavirus cores with the nonstructural glycoprotein NS28

The nonstructural rotavirus receptor glycoprotein NS28 is 175 amino acids long and oriented in the RER membrane with the NH2 terminus on the luminal side and approximately 131 amino acids accessible from the cytoplasmic side. Au et al. (1988) have demonstrated that NS28 is able to interact with rotavirus single-shelled particles (cores) in a receptor:ligand interaction in which NS28 appears to act as the receptor and the rotavirus core as the ligand. This interaction appears to model the events that occur in the infected cell in which virus maturation involves budding of the core into the lumen of the RER. We have investigated the nature of the interaction between cores and NS28 in vitro using membranes derived from SA11 rotavirus-infected MA104 cells and membranes from cells where NS28 and other rotavirus proteins have been expressed using a series of recombinant vaccinia viruses that incorporate appropriate cloned rotavirus genes. The interaction between the core and the receptor is enhanced by the presence of Ca2+ and Mg2+ and Scatchard analysis yields a dissociation constant (Kd) of 5 x 10(-11) M. The major core protein VP6 is the ligand involved because (i) a monoclonal antibody specific for VP6 blocks the reaction, (ii) membranes prepared from cells infected with a double recombinant vaccinia virus which expresses both NS28 and VP6 exhibit a reduced capacity to bind cores, and (iii) VP6 prepared from virus blocks the ability of membranes to bind cores. When VP6, VP7, VP4, and NS28 are expressed singly as the sole viral proteins present in the cell, only membranes from cells expressing NS28 mediate receptor function, indicating that the presence of NS28 is sufficient to mediate the interaction between cores and the membrane and that other viral proteins probably are not involved in the initial receptor:ligand interaction.