Table 2.
Effects of mutations at position 1 of the HA fusion peptide: composite data from studies a and b
| Amino acid | Study | Lipid mixing (study a) | Fusion pores (study a) | Content mixing (study a) | Syncytia formation (study b) |
|---|---|---|---|---|---|
| Gly | a,b | + | + | + | + |
| Ala | a,b | + | + | ± | ± |
| Ser | a,b | + | − | − | − |
| Val | a | − | nd | − | nd |
| Glu | a | − | nd | − | −a |
| Gln | a | − | nd | − | nd |
| His | b | nd | nd | nd | − |
| Leu | b | nd | nd | nd | − |
| Ile | b | nd | nd | nd | − |
| Lys | a | − | nd | − | nd |
| Phe | b | nd | nd | nd | − |
Study a is the current study. Study b is Steinhauer et al. (1995). Amino acids are rank-ordered by side-chain volume; values for residues not listed in Table 1 are (in Å3) His, 167.3; Leu, 167.9; Ile, 168.8; Phe, 203.4. In study b, Steinhauer et al. (1995) reported that Gly1Ala showed reduced syncytia-forming activity and that a synthetic Gly1Ala fusion peptide showed 50% hemolytic activity. Walker and Kawaoka (1993) showed that the mutation Gly1Ala in an H5 HA showed ∼40% syncytia-forming activity.
Lack of lipid mixing, content mixing, and syncytia formation have also been observed with Gly1Glu HA from the Japan strain of influenza (Gething et al., 1986; Guy et al., 1992; Schoch and Blumenthal, 1993).