Biochim Biophys Acta Proteins Proteom 2019 Mar 13;1867(3):175-183. Epub 2018 Dec 13.
Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina; Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina. Electronic address:
Calreticulin (CRT) is a calcium-binding protein that participates in several cellular processes including the control of protein folding and homeostasis of Ca. Its folding, stability and functions are strongly controlled by the presence of Ca. The oligomerization state of CRT is also relevant for its functions. We studied the thermal transitions of monomers and oligomers of CRT by differential scanning calorimetry (DSC), circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) in the presence and absence of Ca. We found three and two components for the calorimetric transition in the presence and absence of Ca respectively. The presence of several components was also supported by CD and FTIR spectra acquired as a function of the temperature. The difference between the heat capacity of the native and the unfolded state strongly suggests that interactions between protein domains also contribute to the heat uptake in a calorimetry experiment. We found that once unfolded at high temperature the process is reversible and the native state can be recovered upon cooling only in the absence of Ca. We also propose a new simple method to obtain pure CRT oligomers.