Thermal stabilities of lupin seed conglutin gamma protomers and tetramers

Various experimental approaches have been used in this work to assess the thermal stabilities of lupin seed conglutin gamma at two pH values, 4.5 and 7.5, at which the protein exists as a protomer and a tetramer, respectively. The patterns of thermal unfolding at the two pH values differed significantly; the tetramer aggregated and became insoluble, whereas the protomer was still soluble after thermal treatment. Also, the midpoint transition temperatures were dramatically different, being 60.3 and 75.1 degrees C for the protomer and tetramer, respectively. The behavior of conglutin gamma at neutral pH was also affected by disulfide formation/interchange, in that some unfolded protein molecules became covalently stabilized. More detailed analyses by differential scanning calorimetry and indirect fluorescence measurements, using 8-anilino-1-naphthalenesulfonic acid as a probe, confirmed the remarkable differences observed in the thermal stabilities of the two protein forms and allowed models for their unfolding patterns to be drawn.