Virus attachment to cells plays an essential role in viral tropism and disease. Reovirus serotypes 1 and 3 differ in the capacity to target distinct cell types in the murine nervous system and in the efficiency to induce apoptosis. The binding of viral attachment protein sigma1 to unidentified receptors controls these phenotypes. We used expression cloning to identify junction adhesion molecule (JAM), an integral tight junction protein, as a reovirus receptor. JAM binds directly to sigma1 and permits reovirus infection of nonpermissive cells. Ligation of JAM is required for reovirus-induced activation of NF-kappaB and apoptosis. Thus, reovirus interaction with cell-surface receptors is a critical determinant of both cell-type specific tropism and virus-induced intracellular signaling events that culminate in cell death.

Many serotype 3 reoviruses bind to two different host cell molecules, sialic acid and an unidentified protein, using discrete receptor-binding domains in viral attachment protein, 1. To determine mechanisms by which these receptor-binding events cooperate to mediate cell attachment, we generated isogenic reovirus strains that differ in the capacity to bind sialic acid. Strain SA؉, but not SA؊, bound specifically to sialic acid on a biosensor chip with nanomolar avidity. SA؉ displayed 5-fold higher avidity for HeLa cells when compared with SA؊, although both strains recognized the same proteinaceous receptor. Increased avidity of SA؉ binding was mediated by increased k on . Neuraminidase treatment to remove cell-surface sialic acid decreased the k on of SA؉ to that of SA؊. Increased k on of SA؉ enhanced an infectious attachment process, since SA؉ was 50 -100-fold more efficient than SA؊ at infecting HeLa cells in a kinetic fluorescent focus assay. Sialic acid binding was operant early during SA؉ attachment, since the capacity of soluble sialyllactose to inhibit infection decreased rapidly during the first 20 min of adsorption. These results indicate that reovirus binding to sialic acid enhances virus infection through adhesion of virus to the cell surface where access to a proteinaceous receptor is thermodynamically favored.

Reovirus attachment to cells is mediated by the binding of viral attachment protein 1 to junctional adhesion molecule 1 (JAM1). The crystal structure of the extracellular region of human JAM1 (hJAM1) reveals two concatenated Ig-type domains with a pronounced bend at the domain interface. Two hJAM1 molecules form a dimer that is stabilized by extensive ionic and hydrophobic contacts between the N-terminal domains. This dimeric arrangement is similar to that observed previously in the murine homolog of JAM1, indicating physiologic relevance. However, differences in the dimeric structures of hJAM1 and murine JAM1 suggest that the interface is dynamic, perhaps as a result of its ionic nature. We demonstrate that hJAM1, but not the related proteins hJAM2 and hJAM3, serves as a reovirus receptor, which provides insight into sites in hJAM1 that likely interact with 1. In addition, we present evidence that the previously reported structural homology between 1 and the adenovirus attachment protein, fiber, also extends to their respective receptors, which form similar dimeric structures. Because both receptors are located at regions of cellcell contact, this similarity suggests that reovirus and adenovirus use conserved mechanisms of entry and pathways of infection.