Modified FGF4 signal peptide inhibits entry of herpes simplex virus type 1

Entry of herpes simplex virus type 1 (HSV-1) into host cells occurs through fusion of the viral envelope with the plasma membrane and involves complex and poorly understood interactions between several viral and cellular prot eins. One strategy for dissecting the function of this fusion machine is th rough the use of specific inhibitors. We identified a peptide with antivira l activity that blocks HSV-1 infection at the entry stage and during cell-t o-tell spreading. This peptide (called EB for "entry blocker") consists of the FGF4 signal sequence with an RRKK tetramer at the amino terminus to imp rove solubility. The activity of EB depends exclusively but not canonically on the signal sequence. Inhibition of virus entry (hrR3) and plaque format ion (BOS) strongly depend on virus concentrations and serum addition, with 50% inhibitory concentrations typically ranging from 1 to 10 muM Blocking p readsorbed virus requires higher EB concentrations. Cytotoxic effects (tryp an blue exclusion) are first noted at 50 muM EB in serum-free medium and at greater than or equal to 200 muM in the presence of serum. EB does not aff ect gC-dependent mechanisms of virus attachment and does not block virus at tachment at 4 degreesC. Instead, EB directly interacts with virions and ina ctivates them irreversibly, without, however disrupting their physical inte grity as judged by electron microscopy. At subvirucidal concentrations, EB changes the adhesive properties of virions, causing aggregation at high vir us concentrations. This peptide may he a useful tool for studying viral ent ry mechanisms.