Conformational stability and thermodynamic characterization of the lipoic acid bearing domain of human mitochondrial branched chain alpha-ketoacid dehydrogenase.

The lipoic acid bearing domain (hbLBD) of human mitochondrial branched chain alpha-ketoacid dehydrogenase (BCKD) plays important role of substrate channeling in oxidative decarboxylation of the branched chain alpha-ketoacids. Recently hbLBD has been found to follow two-step folding mechanism without detectable presence of stable or kinetic intermediates. The present study describes the conformational stability underlying the folding of this small beta-barrel domain. Thermal denaturation in presence of urea and isothermal urea denaturation titrations are used to evaluate various thermodynamic parameters defining the equilibrium unfolding. The linear extrapolation model successfully describes the two-step; native state <-->denatured state unfolding transition of hbLBD. The average temperature of maximum stability of hbLBD is estimated as 295.6 +/- 0.9 K. Cold denaturation of hbLBD is also predicted and discussed.