Определение термодинамических параметров связывания и характер взаимодействия гемагглютинина вируса гриппа А/BANGKOK/1/1979 (Н3N2) с липосомами из фосфатидилхолина
The study of interaction between surface viral proteins and model phospholipids is important for learning more details about the mechanisms of viral penetration into cells during infection. Suitable systems for modeling a cell membrane are liposomes. The binding of hemagglutinin (HA) of influenza virus with phosphatidylcholine liposomes was studied by equilibrium adsorption. It was interesting to identify changes that occur in the protein structure when a protein molecule transitions from the surface into the interior of the membrane. In this work, we studied the following characteristics of the protein-lipid interaction during the formation of a complex of HA with phospholipids: adsorption of HA on a phospholipid bilayer. Using the Scatchard equation and the Gibbs-Helmholtz equation at pH 4.0 and 6.0 thermodynamic parameters were determined. The results concluded the hydrophobic type of interaction between viral protein and liposomes. The additional confirmation of hydrophobic protein-lipid interaction presence was determination of hemagglutinin distribution constants in two-phase systems: dextran-polyethylene glycol (K1) and dextran-polyethylene glycol esterified with palmitic acid (K2). The presence of hydrophobic interaction between HA and the liposome membrane was also confirmed using the quenching method of intrinsic protein fluorescence by a neutral quencher with acrylamide. At pH = 4.0, an increase in the Stern-Volmer quenching constant was observed for the HA + liposome from phosphatidylcholine system, which is caused by structural changes in HA upon incorporation into the liposome bilayer. The fluorescence quenching rate constants calculated using the Stern-Volmer equation indicate a static quenching mechanism in which the quencher interacts with fluophors of a stationary protein molecule. The obtained results are interesting for not only studying virus and cell fusion theoretically, but also have practical applications. Using values of protein-bilayer binding constant and free energy constant, it is possible to select the optimal phospholipid composition of liposomes or virosomes to obtain a stronger complex with various viral proteins. With two-phase systems, it is possible to determine the presence of hydrophobic sites on the viral protein surface, which can be used for evaluation both protein-lipid and protein-protein interaction.