Molecular dynamics simulations of human serum albumin and role of disulfide bonds.

Atomistic molecular dynamics simulations of human serum albumin in the presence and absence of disulfide bonds are presented. Simulations of 70 ns duration provide information on the relevance of disulfide bonds in the dynamics and structural conformation of HSA. Significant conformational changes are observed in the absence of disulfide bonds after 35 ns that could impact the functionality and stability of the protein. Changes in the secondary structure, hydrogen bonds, B factors, and cross-correlations reveal which disulfide bonds are important for keeping the secondary and tertiary structure and dynamics of the protein (e.g., Cys168-Cys177, Cys278-Cys289) and which have little effect on the local structure and dynamics (e.g., Cys200-Cys246, Cys461-Cys477). Removing all disulfide bonds in the protein appears to be a practical prescreening tool for identifying disulfide bonds relevant to structure and dynamics. In the absence of disulfide bonds, certain hydrogen bonds and correlated motions vanish, affecting the structure of neighboring residues. The structure of the primary binding sites of HSA is partially affected when disulfide bonds are removed. For the native structure, simulations clearly reveal the conformational changes that allow the only free cysteine to be exposed on the protein surface to form intermolecular disulfide bonds; this information could not be resolved from the static crystal structure alone. The absence of specific disulfide bonds could lead to partially unfolded structures; such structures are known to be prone to protein aggregation. Removing disulfide bonds could have similar consequences in other proteins of interest, such as immunoglobulin G.