It is very evident that salt bridges are sensitive to pH changes and the low pH causes breakage of salt bridges. This results in interaction of negatively charged Asp or Glu amino acids with the solvent. This interaction would in turn leads to an enhanced net positive charge in the region, resulting in repulsion and partial dissociation of HA1 and HA2 domains. Taking this assumption as a cue, the present work aims

1. Make and break the salt linkages in the HA molecule from X-31 strain.

2. To either destabilize or stabilize the HA protein with respect to salt bridges, and thereby determine the contribution of electrostatic interactions towards HA protein stability.

3. Investigate to determine the important amino acids that are responsible for the stability of the non-fusogenic HA at neutral pH.

4. Experimentally prove the protonation model and there by the metastability of HA protein at low pH.

5. To correlate the mutants with naturally existing variants and based on the results derive a model for early steps of conformational changes leading to successful fusion.