A theoretical study of the unfolding pathway of reduced human serum albumin.

The unfolding of the reduced human serum albumin (HSA) was simulated by generating four molecular dynamics (MD) trajectories of 160 ns each at 350, 375, 400, and 425 K, respectively. A principal components analysis (PCA) was performed on the four trajectories. Based on this analysis, 17 representative protein conformers were identified and subsequently used to construct a sequence of partially unfolded structures. They were ordered according to their decreasing α-helix fractions. The structural evolution in this unfolding sequence was found to be continuous at global but also at local level supporting the hypothesis that the protein unfolding pathway is not significantly dependent on the simulation temperature. As a result, the α-helix fraction of the protein appears to be a good reaction coordinate for the unfolding process, as it was previously suggested by experiments. Based on this observation, two conformers in the unfolding sequence were predicted to be close to the equilibrium structure of reduced HSA thus providing a first theoretical model for this protein form.