Organization and dynamics of Trp14 of hemagglutinin fusion peptide in membrane mimetic environment.

The fusion peptide of influenza hemagglutinin (HA) is important for cellular entry of influenza virus. Previous studies showed that HA fusion peptide assumes a bent structure in membrane environment, which is extremely important for its fusion-promoting activity. In this work, we have measured the organization and dynamics of the tryptophan (Trp14) residue in presence of sodium dodecyl sulfate (SDS) to investigate the conformational flexibility of tryptophan in membrane-mimetic environment. The steady state and time-resolved fluorescence measurements were employed to investigate the location and rotational flexibility of the tryptophan residue in the SDS micelles. We have calculated the apparent rotational correlation time of Trp14 from the fluorescence anisotropy and fluorescence lifetime data, and apparent rotational correlation time shows a substantial increase in presence of SDS. We have further measured the red edge excitation shift (REES) of Trp14 fluorescence in absence and in presence of two different concentrations of SDS. A large magnitude of REES at post-micellar concentration of SDS indicates the polar confined environment of Trp14 residue in the micellar milieu. Taken together, our results confirm that the tryptophan is located in a motionally restricted interfacial region of micelles. The interfacial location and slow dynamics of Trp14 might be important to adopt the appropriate structure of HA fusion peptide in membrane environment.