Molecular dynamics of biomolecules at interfaces: Insulin-insulin interactions

Understanding the intermolecular forces and dynamics of insulin self-assembly is crucial for devising formulations for the treatment of insulin-dependent diabetes. Insulin must dissociate from its hexameric storage form, through an intermediate dimer form, to the bioactive monomer before receptor binding. Specifically, the dimer dissociation is a pivotal step to control insulin dynamics and self-assembly.;Steered molecular dynamics simulations were performed on native insulin to provide molecular insight into the insulin dissociation force spectroscopy experiment. Our simulation results of force-induced dimer dissociation revealed that the dimer dissociation occurs near the limit of extensibility of the B-chain with significant conformational changes to the monomer(s). These long-range interactions, consistent with our experiments, are due to stronger inter-monomer interactions across the anti-parallel beta-sheet interface than any other intra-monomer interaction. Novel atomistic data played an important role in detailed structural characterization of multiple unfolding and dissociation pathways that depend on the relative strength of the inter-monomer interactions and the intra-monomer interactions. Comparative simulations of two rapid-acting insulin analogues (LysB28ProB29, Asp B28) to native insulin were performed to investigate the effect of sequence on the dimer dissociation. The hypothesis is that site-specific alterations to the dimer-forming surface of two rapid-acting analogues will result in a weakening of the inter-monomer interactions, which would be reflected during force-induced dimer dissociation. The results revealed that these analogues dissociates with lower probability of long-range interactions and a corresponding reduction in B-chain extension. B-chain extensibility is thus a characteristic marker of inter-monomer interactions and multiple unfolding pathways. These data agree with the design strategies of sequence modifications to the weakened inter-monomer interface applied to the synthesis of rapid-acting insulin analogues.;In contrast, the ligand-induced alteration to the strengthened inter-monomer interactions through a specific GluB13s-zinc bridge contributed to the unique unfolding force curves, so it can be applicable as design strategy to the development of a novel long-acting analogue. Overall, our force spectroscopy studies on insulin native and analogues have successfully provided atomistic insights into the dimer dissociation characteristics and control strategies of self-assembly. In addition, this study would provide a framework for the structure-dynamics-function relationships of insulin-insulin receptor binding.