ИСТИНА

Recently, small-angle scattering (SAXS), analytical ultracentrifugation (AUC) and atomic force microscopy (AFM) were employed to characterize the overall structure and association behavior of the full length Influenza А Virus matrix protein M1 at acidic pH [1]. This condition occurs at the very beginning of cell infection leading to an acid-triggered fusion of the viral membrane. Moreover, change of pH was found to serve as a switch that allowed M1 to carry out its multiple functions in the uncoating, nuclear transport, and assembly of the viral ribonucleocapsid [2]. It is well known also that the isolated M1 can be soluble without detergents only at pH < 5.0 [3]. Still, it was demonstrated that the M1 self-assembly occurs even at acidic pH: SAXS and AFM experiments revealed well ordered structures formed by M1 both in solution and on the lipid bilayer. These helix-like shapes could be treated as pre-matrix protein superstructures, whose formation is an intrinsic biological property of the M1 protein. It can be assumed, however, that the oligomerization tendency of M1 should increase with pH. The aim of the present work was to analyse the structure and self-assembly of M1 at gradually changing pH (up to the neutral pH condition) in solution and on the bare mica surface using SAXS and AFM, correspondingly. We found that the oligomerization processes occur in a similar way in the solution and on the substrate, and quantitatively described these processes. Moreover, pH 6.0 was found to be the condition at which binding between M1 molecules starts to break. Our results provide new insights into the mechanism of M1 to form matrix and virus-like particles alone without partners and give a basis for a further analysis of the hierarchy of M1 in the virus life cycle. This work was supported in part by German Ministry of Education and Science (BMBF) project BIOSCAT (Grant 05K20912), and by Russian Foundation for Basic Researches (project 15-54-74002 EMBL_а). References 1. E. Shtykova et al. PLoS One, 8, (2013) e82431. 2. M. Bu et al. J. Virology, 70, (1996) 8391-8401. 3. O. Zhirnov. Virology, 186, (1992) 324-330.