SPECTROSCOPIC AND THERMODYNAMIC EVIDENCE FOR A COMPLEX DENATURATION MECHANISM OF BOVINE BETA-LACTOGLOBULIN-A

We present a spectroscopic and calorimetric study on the thermal denat uration of bovine beta-lactoglobulin (beta-lg) variant A. Spectroscopi c data allowed detection of a stable intermediate emerging from struct ural modifications restricted to local regions of the native molecule. It is suggested that this kind of intermediate could be a common prop erty of lipocalins. Using the same set of parameters that has successf ully related thermodynamics and structural properties of other protein s, it is shown that the thermally denatured state of beta-lg retains a significant amount of buried hydrophobic surface area. Thus, despite being a small protein composed of a single structural domain, beta-lg exhibits a complex unfolding mechanism, comprising at least two other species different from the native and completely unfolded states.