Abstract
CD55, or decay-accelerating factor (DAF), is a cell surface glycoprotein which regulates complement activity by accelerating the decay of C3/C5 convertases. Recently, we and others have established that this molecule acts as a cellular receptor for echovirus 7 and related viruses. DAF consists of five domains: four short consensus repeats (SCRs) and a serine/threonine-rich region, attached to the cell surface by a glycosylphosphatidyl inositol anchor. Chinese hamster ovary cells stably transfected with deletion mutants of DAF or DAF-membrane cofactor protein recombinants were analyzed for virus binding. The results indicate that the binding of echovirus 7 to DAF specifically requires SCR2, SCR3, and SCR4. There is also a nonspecific requirement for the S/T-rich region which probably functions to project the binding region away from the cell membrane. The three nonpeptide modifications of DAF, N-linked glycosylation, O-linked glycosylation, and the glycosylphosphatidyl inositol anchor, are not required for virus binding. The SCRs of membrane cofactor protein, the closest known relative of DAF, cannot substitute for those of DAF with retention of virus binding activity. The monoclonal antibody used to identify DAF as an echovirus receptor, and which inhibits binding of the virus (monoclonal antibody 854), binds to SCR3.