β-structure of the coat protein subunits in spherical particles generated by tobacco mosaic virus thermal denaturation

Conversion of the rod-like tobacco mosaic virus (TMV) virions into ball-like particles by thermal denaturation at 90-98 degrees C had been described by R.G. Hart in 1956. We have reported recently that spherical particles (SPs) generated by thermal denaturation of TMV at 94-98 degrees C were highly stable, RNA-free, and water-insoluble. The SPs were uniform in shape but varied widely in size (53-800 nm), which depended on the virus concentration. Here, we describe some structural characteristics of SPs using circular dichroism, fluorescence spectroscopy, and Raman spectroscopy. It was found that the structure of SPs protein differs strongly from that of the native TMV and is characterized by coat protein subunits transition from mainly (about 50%) alpha-helical structure to a structure with low content of alpha-helices and a significant fraction of beta-sheets. The SPs demonstrate strong reaction with thioflavin T suggesting the formation of amyloid-like structures.