Targeted Molecular Dynamics Simulation of Conformational Change-Application to the T ↔ R Transition in Insulin

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Abstract
A novel method to calculate transition pathways between two known protein conformations is presented. It is based on a molecular dynamics simulation starting from one conformational state as initial structure and using the other for a directing constraint. The method is exemplified with the T ↔ R transition of insulin. The most striking difference between these conformational states is that in T the 8 N-terminal residues of the B chain are arranged as an extended strand whereas in R they are forming a helix. Both the transition from T to R and from R to T were simulated. The method proves capable of finding a continuous pathway for each direction which are moderately different. The refolding processes are illustrated by a series of transient structures and pairs of Ø, ψ angles selected from the time course of the simulations. In the T → R direction the helix is formed in the →last third of the transition, while in the R → T direction it is preserved during more than half of the simulation period. The results are discussed in comparison with those of an atternative method recently apptied to the T → R transition of insulin which is based on targeted energy minimisation.