A LEUCINE-ZIPPER MOTIF IN THE ECTODOMAIN OF SENDAI VIRUS FUSION PROTEIN ASSEMBLES IN SOLUTION AND IN MEMBRANES AND SPECIFICALLY BINDS BIOLOGICALLY-ACTIVE PEPTIDES AND THE VIRUS

We have detected a leucine zipper-like motif in the ectodomain of the Sendai virus fusion protein (aa 269-307) which is extremely conserved in the family of Sendai viruses, To find a possible role for this moti f, we synthesized SV-269, a 39 amino acid peptide corresponding to thi s domain, and a mutant peptide, MuSV-269, with an amino acid pair inte rchanged their positions. The peptides were labeled with fluorescent p robes at their N-terminal amino acid and functionally and structurally characterized, The data show that SV-269, but not MuSV-269, specifica lly binds Sendai virus. Expectedly, SV-269 is more active than the mut ant MuSV-269 in inhibiting Sendai virus-mediated hemolysis. Fluorescen ce studies reveal that SV-269 assembles in aqueous solution, binds to zwitterionic PC and negatively-charged PS/PC vesicles, and assembles t herein, Although MuSV-269 similarly binds to both types of vesicles, i t only slightly assembles in solution and nor at all in membranes. Mor eover, SV-269, but not MuSV-269, coassembles with the biologically-act ive heptad repeats SV-150 and SV-473 (Rapaport et al., 1995) in soluti on as revealed by fluorescence and circular dichroism (CD) spectroscop y, and with SV-150 within negatively-charged PS/PC and zwitterionic PC vesicles, Despite these differences, both SV-269 and MuSV-269 adopt s imilar secondary structures in 40% TFE and 1% SDS as revealed by CD sp ectroscopy, and disrupt the packing of the lipid bilayers to the same extent, as shown by the dissipation of diffusion potential, The role o f this leucine zipper motif is discussed in terms of the assembly of t he Sendai virus fusion protein in solution and within membranes, Since most of the heptadic leucines are also conserved in the corresponding domains of other paramyxoviruses such as rinderpest, measles, SV5, an d parainfluenza, it may indicate a similar role of this domain in thes e viruses as well.