Denaturation of apolipoprotein A‐I and the monomer form of apolipoprotein A‐IMilano

In this study the thermal and denaturant induced unfolding of apolipoprotein A‐I (apo A‐I) and the monomer form of apolipoprotein A‐I Milano (apo A‐I M ) was followed. Dimer apo A‐I M was reduced with dithiothreitol, which was present in the protein solutions in all experiments. Thermal denaturation is followed by differential scanning calorimetry (DSC) and far‐UV and near‐UV CD. Both apo A‐I and monomer apo A‐I M have a broad asymmetric DSC peak that could be deconvoluted into three non two‐state transitions, apo A‐I being more stable than the monomer apo A‐I M . Estimation of melting of tertiary structure by near‐UV CD is lower than that for secondary structure determined from far‐UV. This together with the non two‐state unfolding of the proteins observed with DSC is indicative of unfolding via a molten globular‐like state. Apo A‐I and monomer apo A‐I M are equally susceptible to guanidinum chloride, half‐unfolded at 1.2 m denaturant. The presence of 0.5 and 1.0 m denaturant, lower and equalize the denaturation temperatures of the proteins, respectively.