Tritium planigraphy: Differences in the spatial structures of the influenza virus M1 protein in crystal, solution, and virion

The structure of the M1 protein of the influenza virus A/Puerto Rico/8/34 (PR8, subtype H1N1) in solution at acidic pH and in the composition of the virion has been studied by the tritium planigraphy method. A model of the spatial structure was constructed using a special algorithm simulating the experiment and a set of algorithms for predicting the secondary structure and disordered regions in proteins. The tertiary structure was refined using the Rosetta program. For a comparison of the structures in solution and inside the virion, the data of Xray diffraction analysis for the NM domain were also used. The main difference in the structures of the protein in solution and the crystalline state is observed in the region of contact of N and M domains, which in the crystalline state is packed more densely. The regions of the maximum label incorpora� tion almost completely coincide with unstructured regions in the protein that were predicted by the bioinfor� matics analysis. These regions are concentrated in the C domain and in loop regions between M, N, and C domains. The data were confirmed by analytical centrifugation and dynamic light scattering. Anomalous hydrodynamic dimensions and a low structuration of the M1 protein in solution were found. The polyfunc� tionality of the protein in the cell is probably related to its flexible tertiary structure, which, owing to unstruc� tured regions, provides contact with various partner molecules.