Study of rabies virus by Differential Scanning Calorimetry.

Differential Scanning Calorimetry (DSC) has been used in the past to study the thermal unfolding of many different viruses. Here we present the first DSC analysis of rabies virus. We show that non-inactivated, purified rabies virus unfolds cooperatively in two events centered at approximately 62 and 73 °C. Beta-propiolactone (BPL) treatment does not alter significantly viral unfolding behavior, indicating that viral inactivation does not alter protein structure significantly. The first unfolding event was absent in bromelain treated samples, causing an elimination of the G-protein ectodomain, suggesting that this event corresponds to G-protein unfolding. This hypothesis was confirmed by the observation that this first event was shifted to higher temperatures in the presence of three monoclonal, G-protein specific antibodies. We show that dithiothreitol treatment of the virus abolishes the first unfolding event, indicating that the reduction of G-protein disulfide bonds causes dramatic alterations to protein structure. Inactivated virus samples heated up to 70 °C also showed abolished recognition of conformational G-protein specific antibodies by Surface Plasmon Resonance analysis. The sharpness of unfolding transitions and the low standard deviations of the Tm values as derived from multiple analysis offers the possibility of using this analytical tool for efficient monitoring of the vaccine production process and lot to lot consistency.