Why is a specific amino acid sequence of F glycoprotein required for the membrane fusion reaction between envelope of HVJ (Sendai virus) and target cell membranes?

Since homology among the fusogenic sequences of the F glycoprotein of paramyxoviruses is high compared with other hydrophobic sequences such as transmembrane sequences and signal peptides, specific binding of this segment to some membrane component was suspected. Thus, temperature-dependent binding of cholesterol to F protein was found. A virus inhibitory peptide (Z-D-Phe-L-Phe-Gly) was found to bind to virus particles also temperature dependently. These dependency are very similar to that of the fusion reaction. Binding of cholesterol and the peptide to the fusogenic sequence of F protein was suggested based on construction of molecular models. Importance of these bindings for understanding the fusion mechanism is discussed.