Intrinsic Fluorescence as a Probe of Structural Dynamics and Interactions of Human Adenovirus with Surfactants and Liposomes.

In this work, the intrinsic fluorescence of Human Adenovirus serotype 2 (HAdV-2), arising from tryptophan (Trp) and tyrosine (Tyr) residues present in viral proteins, was used to monitor structural changes in the three-dimensional organization of the viral particle as a function of the inactivation method employed (UV irradiation or paraformaldehyde (PFA) treatment), temperature, and the presence of negatively and positively charged surfactants. Steady-state fluorescence anisotropy was used to investigate the interaction between HAdV-2 and zwitterionic or negatively charged liposomes by monitoring both the extrinsic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) inserted into the lipid bilayer and the intrinsic anisotropy of Trp residues from viral proteins. Tyr fluorescence emission proved to be more sensitive to temperature variations, whereas Trp emission was more strongly affected in samples inactivated with PFA. In the presence of surfactants, stronger interactions were observed with negatively charged micelles, resulting in enhanced Tyr fluorescence and quenched Trp fluorescence. The most pronounced effect was observed for the interaction between HAdV-2 and negatively charged 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol), sodium salt (DPPG) liposomes. In the presence of viral particles, the phase transition temperature (Tm) of DPPG liposomes increased by approximately 11 °C, while no detectable structural changes were observed in the three-dimensional organization of the viral particle itself. Overall, these results highlight intrinsic fluorescence as a valuable approach for probing the structural organization of HAdV-2 under different environmental and interfacial conditions.