Structural Polymorphs of Self-Assembled Brome Mosaic Virus Capsid Protein

Brome Mosaic Virus (BMV), Cowpea Chlorotic Mottle Virus (CCMV), and Tobacco Mosaic Virus (TMV) are among the few viruses that can be reconstituted in infectious form from their purified components (RNA and capsid protein (CP)), each under special pH and ionic strength conditions. In the latter two cases, extensive studies have been carried out with capsid protein alone, exploring the structural polymorphs that result from self-assemblies corresponding to a broad range of pH and ionic strength. In the present work, we map out the polymorph distribution for BMV, using electron microscopy and atomic force microscopy (AFM), to elucidate the types of quaternary structures that arise. They include spherical, rodlike, and sheet-like assemblies of capsid proteins. We demonstrate that these self-assembled polymorphs are independent of their pH/ionic strength path history and can be reversibly interconverted.