Macroscopic aggregation of tobacco mosaic virus coat protein

The relationship between processes of thermal denaturation and heat-induced aggregation of tobacco mosaic virus (TMV) coat protein (CP) was studied. J udging from differential scanning calorimetry "melting" curves, TMV CP in t he form of a trimer-pentamer mixture ("4S-protein") has very low thermal st ability, with a transition temperature at about 40 degreesC. Thermally dena tured TMV CP displayed high propensity for large (macroscopic) aggregate fo rmation. TMV CP macroscopic aggregation was strongly dependent on the prote in concentration and solution ionic strength. By varying phosphate buffer m olarity, it was possible to merge or to separate the denaturation and aggre gation processes. Using far-UV CD spectroscopy, it was found that on therma l denaturation TMV CP subunits are converted into an intermediate that reta ins about half of its initial alpha -helix content and possesses high heat stability. We suppose that this stable thermal denaturation intermediate is directly responsible for the formation of TMV CP macroscopic aggregates.