Molecular Dynamics Study of Insulin Mutants

Abstract

Human insulin, a small protein hormone consisting of A-chain (21 residues) and B-chain (30 residues) linked by three disulfide bonds, is crucial for controlling the hyperglycemia in type I diabetes. In the present work molecular dynamics simulation (MD) with human insulin and its mutants was used to assess the influence of 10 point mutations (His^A8, Val^A10, Asp^B10, Gln^B17, Ala^B17, Gln^B18, Asp^B25, Thr^B26, Glu^B27, Asp^B28), 6 double mutations (Glu^A13+Glu^B10, Ser^A13+Glu^B27, Glu^B1+Glu^B27, Ser^B2+Asp^B10, Asp^B9+Glu^B27, Glu^B16+Glu^B27) and one triple mutation (Glu^A15+Asp^A18+Asp^B3) in the protein sequence on the structure and dynamics of human insulin. A series of thermal unfolding MD simulations with wild type (WT) human insulin and its mutants was performed at 400 K with GROMACS software (version 5.1) using the CHARMM36m force field. The MD results have been analyzed in terms of the parameters characterizing both the global and local protein structure, such as the backbone root mean-square deviation, gyration radius, solvent accessible surface area, the root mean-square fluctuations and the secondary structure content. The MD simulation data showed that depending on time evolution of integral characteristics, the examined mutants can be tentatively divided into three groups: 1) the mutants His^A8, Val^A10, Ala^B17, Asp^B25, Thr^B26, Glu^B27, Glu^A13+Glu^B10, Glu^B1+Glu^B27 and Glu^B16+Glu^B27, which exert stabilizing effect on the protein structure in comparison with wild type insulin; 2) the mutants Gln^B17, Asp^B10, Ser^B2+Asp^B10 and Glu^A15+Asp^A18+Asp^B3 that did not significantly affect the dynamical properties of human insulin with a minimal stabilizing impact; 3) the mutants Asp^B28, Asp^B9+Glu^B27 and Ser^A13+Glu^B27, Gln^B18, destabilizing the protein structure. Analysis of the secondary structure content provided evidence for the influence of Asp^B28, Asp^B9+Glu^B27 and Ser^A13+Glu^B27, Gln^B18 on the insulin unfolding. Our MD results indicate that the replacement of superficial nonpolar residues in the insulin structure by hydrophilic ones gives rise to the increase in protein stability in comparison with the wild type protein.