Flow-induced structural transition in the β-switch region of glycoprotein Ib

The impact of fluid flow on structure and dynamics of biomolecules has recently gained much attention. In this article, we present a molecular-dynamics algorithm that serves to generate stable water flow under constant temperature, for the study of flow-induced protein behavior. Flow simulations were performed on the 16-residue beta-switch region of platelet glycoprotein Ib alpha, for which crystal structures of its N-terminal domain alone and in complex with the A1 domain of von Willebrand factor have been solved. Comparison of the two structures reveals a conformational change in this region, which, upon complex formation, switches from an unstructured loop to a beta-hairpin. Interaction between glycoprotein Ib alpha and von Willebrand factor initiates platelet adhesion to injured vessel walls, and the adhesion is enhanced by blood flow. It has been hypothesized that the loop to beta-hairpin transition in glycoprotein Ib alpha is induced by flow before binding to von Willebrand factor. The simulations revealed clearly a flow-induced loop ->beta-hairpin transition. The transition is dominated by the entropy of the protein, and is seen to occur in two steps, namely a dihedral rotation step followed by a side-group packing step.