The relative unknown conformational stability of monovalent bulks of influenza virus haemagglutinin (HA) from three different strains (B/Guangdong, A/New Caledonia and A/Panama) was investigated with fluorescence and circular dichroism (CD) spectroscopy. Various stress conditions (concentration of denaturant, freeze-thawing, pH and temperature) affected the spectroscopic properties of the haemagglutinin proteins differently. Unfolding experiments revealed a poor stability of Guangdong haemagglutinin (GD-HA) in comparison with New Caledonia (NC-HA) and Panama haemagglutinin (P-HA). Freeze-thawing altered the secondary and tertiary structure of Guangdong haemagglutinin and only the tertiary structure of Panama haemagglutinin. From pH 4.6-9.2 the tertiary structures of Guangdong, New Caledonia and Panama haemagglutinin were all affected to a different extent. The secondary structure was only altered at low pH. Incubation of haemagglutinin at 60°C resulted in denaturation of the protein and a dramatic change of the fluorescence spectrum, indicative of oxidised tryptophan (Trp). In conclusion, fluorescence and circular dichroism spectroscopy are highly suitable techniques to monitor the stability of haemagglutinin in a straightforward and fast way.
- Circular dichroism spectroscopy
- Fluorescence spectroscopy
- Influenza virus haemagglutinin
- Physicochemical characterisation