Analysis of domain movements in glutamine-binding protein with simple models.

In this work, the mechanism of domain movements of glutamine-binding protein (GlnBP), especially the influence of the ligand on GlnBP dynamic behavior is investigated with the aid of a Gaussian network model (GNM) and an anisotropy elastic network model. The results show that the "open-closed" transition mainly appears as the large movement of the small domain, especially the top region including two alpha-helices and two beta-strands. The slowest mode of each three forms of GlnBP--ligand-free open, ligand-bound closed, and ligand-free closed GlnBP--shows that the open-closed motion of the two domains has a common hinge axis centered on Lys-87 and Gln-183. Accompanying the conformational transition, the residues within both large and small domains move in a highly coupled way. The peaks of the fast modes correspond to residues that were thought, in the GNM, to be important for the stability of the protein, and these residues may be involved in the interactions with the membrane-bound components. With the contacts between the large domain and the small domain increasing, the ability of the "open-closed" motion is decreased. All the results agree well with those of molecular dynamics simulations, and it is thought that the open-closed conformation transition is the nature of the topology structure of GlnBP. Also, the influence of the ligand on GlnBP is studied with a modified GNM method. The results obtained show that the ligand does not influence the closed-to-open transition tendency.