A Differential Scanning Calorimetric Study of Newcastle Disease Virus: Identification of Proteins Involved in Thermal Transitions

The irreversible thermal denaturation of Newcastle disease virus was investigated using different techniques including high-sensitivity differential scanning calorimetry, thermal gel analysis intrinsic fluorescence, and neuraminidase activity assays. Application of a successive annealing procedure to the scanning calorimetric endotherm of Newcastle disease virus furnished four elementary thermal transitions below the overall endotherm; these were further identified as coming from the denaturation of each viral protein. The shape of these transitions, as well as their scan-rate dependence, was explained by assuming that thermal denaturation takes place according to the kinetic schemeN→kD, wherekis a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation;Nis the native state; andDis the denatured state. On the basis of this model, activation energy values were calculated. The data obtained with the other methods used in this work support the proposed two-state kinetic model.