ИСТИНА

Influenza virus M1 protein play important roles during quite different stages of Influenza virus lifecycle, such as virion disassembly and RNPs release during infection, on the one hand, and proper assembly and budding of new viruses on the other. These processes take place at different pH conditions, so the function of M1 is also strongly dependent on pH. Therefore, it is of great interest to investigate the structural changes of M1 protein itself and viral protein scaffold under pH changing. For this reason we combined solution studies of full-length M1 protein using small angle X-ray scattering (SAXS) with atomic force microscopy (AFM) of protein layers on solid support to investigate processes of the protein self-assembly in the whole physiologically relevant range of pH, from 4 to 7. We revealed the tendency of M1 protein to form helical structures, even in acidic medium, and found that the threshold of transition from predominantly monomeric form of the protein to complete helical structures lies at pH around 6, while the structure of the individual protein molecule remains the same. Atomic force microscopy demonstrated fundamental difference in the adsorption of M1 protein on the negatively charged surface in neutral compared to acidic conditions. Performing the measurements of M1 adsorption at different ionic strengths of the solution, we estimated the charge of M1 in the concerned range of pH. Our results show that at pH of late endosome scaffold protein M1 significantly changes its charge meaning that electrostatics could be the main driving force in disassembly of Influenza A virus protein envelope. On the other hand, we demonstrated that assembly of M1 molecules in helices should occur in a pH-independent manner. Modelling these processes using Derjagin-Landau-Verwey-Overbeek theory (DLVO) allows us to estimate the energy of M1-M1 interaction. This work was supported in part by Russian Science Foundation (project 15-04-00060) and Russian Foundation for Basic Researches (project 15-54- 74002 EMBL_а).