Specific binding of recombinant foamy virus envelope protein to host cellscorrelates with susceptibility to infection

The interaction of simian foamy viruses (FVs) with their putative cellular receptor(s) was studied with two types of recombinant envelope protein (Env ). Transient expression of fun-length Env in BHK-21 cells induced syncytia formation. However, selected stable transfectants fused with naive cells bu t not with each other. A soluble fusion protein of the Env surface domain w ith the Fe fragment of a human IgG1 heavy chain (EnvSU-Ig) was produced in the baculovirus expression system, purified to homogeneity, and used for bi nding and competition analyses. EnvSU-Ig but not unrelated lg fusion protei ns bound to cells specifically. Neutralizing serum blocked binding of EnvSU -Ig and, vice versa, serum-mediated neutralization was abrogated by the chi meric protein. Concomitant reduction of EnvSU-Ig binding and Ri susceptibil ity was seen in Env-expressing target cells. Although EnvSU-Ig did not inhi bit FV infection, very likely due to its displacement by multivalent virus- cell interactions, this divalent ligand should help to characterize functio nally and to identity the ubiquitous FV receptor. (C) 1999 Academic Press.