A σ1 region important for hemagglutination by serotype 3 reovirus strains

Hemagglutination (HA) by the mammalian reoviruses is mediated by interactions between the viral σ1 protein and sialoglycoproteins on the erythrocyte surface. Three serotype 3 (T3) reovirus strains were identified that do not agglutinate either bovine or type O human erythrocytes (HA negative): T3 clone 43 (T3C43), T3 clone 44 (T3C44), and T3 clone 84 (T3C84). These three strains also showed a diminished capacity to bind the major erythrocyte sialoglycoprotein, glycophorin, in an enzyme-linked immunosorbent assay. To determine the molecular basis for these findings, we examined the deduced σ1 amino acid sequences of the three HA-negative T3 strains and four HA-positive T3 strains. The limited number of sequence differences in the σ1 proteins of these seven strains allowed us to identify single unique amino acid residues in each of the HA-negative strains (aspartate 198 in T3C43, leucine 204 in T3C44, and tryptophan 202 in T3C84) that cluster within a discrete region of the σ1 tail. The identification of σ1 residues important for HA and glycophorin binding suggests that tail-forming sequences are exposed on the virion surface, where they interact with carbohydrate residues on the surface of cells.