STOPPED-FLOW, CLASSICAL, AND DYNAMIC LIGHT-SCATTERING ANALYSIS OF MATRIX PROTEIN-BINDING TO NUCLEOCAPSIDS OF VESICULAR STOMATITIS-VIRUS

During the process of assembly of enveloped viruses, binding of the nu cleoprotein core of the virus (nucleocapsid) to the host membrane is m ediated by the viral matrix (M) protein. Light scattering properties o f vesicular stomatitis virus (VSV) nucleocapsids and nucleocapsid-M pr otein (NCM) complexes assembled in vivo were determined following solu bilization of the virion envelope with detergents at varying ionic str ength to vary the extent of M protein binding. Three factors were foun d to contribute to the light scattering properties of VSV nucleocapsid s: their conformation, extent of self-association, and amount of bound M protein. All three were affected by changes in ionic strength but c ould be distinguished by several parameters. Conformational changes in nucleocapsids and NCM complexes occurred rapidly (millisecond time sc ale) upon changing salt concentration and were reflected in changes in the angular dependence of light scattering intensity (i.e., changes i n radius of gyration, R(G)). Changes in extent of self-association occ urred relatively slowly (seconds to minutes time scale) and could be d istinguished by the concentration dependence of the apparent molecular mass and diffusion coefficient of the NCM complex. Changes in M prote in binding occurred on an intermediate time scale (t(1/2) approximatel y 1 s) and reflected changes in both molecular mass and R(G). The data presented here provide criteria for assessing binding of M protein to nucleocapsids under conditions of minimal perturbation of the NCM com plex assembled in vivo and at low protein concentrations so that self- association of the NCM complex was minimal and reversible.