The folding of the α-helix domain hbSBD of the mammalian mitochondrial branched-chain α-ketoacid dehydrogenase complex is studied by the circular dichroism technique in absence of urea. Thermal denaturation is used to evaluate various thermodynamic parameters defining the equilibrium unfolding, which is well described by the two-state model with the folding temperature TF = 317.8 ± 1.95 K and the enthalpy change ΔHG = 19.67 ±2.67 kcal/mol. The folding is also studied numerically using the off-lattice coarse-grained Go model and the Langevin dynamics. The obtained results, including the population of the native basin, the free-energy landscape as a function of the number of native contacts, and the folding kinetics, also suggest that the hbSBD domain is a two-state folder. These results are consistent with the biological function of hbSBD in branched-chain α-ketoacid dehydrogenase.
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