Identification of a leucine zipper motif in the ectodomain of sendai virus fusion protein which assembles in solution and in the membrane and specifically binds the virus

We have detected a leucine zipper-like motif in the ectodomain of Sendal virus fusion protein (a. a. 269-307) which is extremely conserved in the family of Sendal viruses. In order to find out a possible role of this motif, a thirty nine residue peptide corresponding to this domain, designated SV-269, and a mutant peptide, MuSV-269, with a heptadic leucine and glutamic acid interchanged their positions, were synthesized and labeled with fluorescent probes at their N-terminal amino acids. We found that the wild type SV-269 specifically binds Sendal virus, whereas MuSV-269 cannot. Fluorescence studies were carried out to characterize their binding to membrane, assembly in membrane and in aqueous solution and ability to disturb the packing of the lipid bilayer. Circular dichroism experiments were performed to determine the secondary structure of the peptides in 40% TFE and 1% SDS. The data suggest a possible rote of this putative leucine zipper motif in the assembly of the Sendal virus fusion protein in solution and membrane. Since most of the heptadic leucines are also conserved in the corresponding domains of other paramyxoviruses like rinderpest, measels, SV5 and para-influenza, it may indicate a similar role of this domain in these viruses as welt.