Thermodynamic characterization of the conformational stability of the homodimeric protein, pea lectin

The conformational stability of the homodimeric pea lectin was determined b y both isothermal urea-induced and thermal denaturation in the absence and presence of urea. The denaturation profiles were analyzed to obtain the the rmodynamic parameters associated with the unfolding of the protein. The dat a not only conform to the simple A(2) double left right arrow 2U model of u nfolding but also are well described by the linear extrapolation model for the nature of denaturant-protein interactions. In addition, both the confor mational stability (Delta G(s)) and the Delta C-p for the protein unfolding is quite high, at about 18.79 kcal/ mol and 5.32 kcal/(mol K), respectivel y, which may be a reflection of the relatively larger size of the dimeric m olecule (M-r 49 000) and, perhaps, a consequent larger buried hydrophobic c ore in the folded protein. The simple two-state (A(2) double left right arr ow 2U) nature of the unfolding process, with the absence of any monomeric i ntermediate, suggests that the quaternary interactions alone may contribute significantly to the conformational stability of the oligomer-a point that may be general to many oligomeric proteins.