title: Ras conformational switching: simulating nucleotide-dependent conformational transitions with accelerated molecular dynamics.
abstract: Ras mediates signaling pathways controlling cell proliferation and development by cycling between GTP- and GDP-bound active and inactive conformational states. Understanding the complete reaction path of this conformational change and its intermediary structures is critical to understanding Ras signaling. We characterize nucleotide-dependent conformational transition using multiple-barrier-crossing accelerated molecular dynamics (aMD) simulations. These transitions, achieved for the first time for wild-type Ras, are impossible to observe with classical molecular dynamics (cMD) simulations due to the large energetic barrier between end states. Mapping the reaction path onto a conformer plot describing the distribution of the crystallographic structures enabled identification of highly populated intermediate structures. These structures have unique switch orientations (residues 25-40 and 57-75) intermediate between GTP and GDP states, or distinct loop3 (46-49), loop7 (105-110), and alpha5 C-terminus (159-166) conformations distal from the nucleotide-binding site. In addition, these barrier-crossing trajectories predict novel nucleotide-dependent correlated motions, including correlations of alpha2 (residues 66-74) with alpha3-loop7 (93-110), loop2 (26-37) with loop10 (145-151), and loop3 (46-49) with alpha5 (152-167). The interconversion between newly identified Ras conformations revealed by this study advances our mechanistic understanding of Ras function. In addition, the pattern of correlated motions provides new evidence for a dynamic linkage between the nucleotide-binding site and the membrane interacting C-terminus critical for the signaling function of Ras. Furthermore, normal mode analysis indicates that the dominant collective motion that occurs during nucleotide-dependent conformational exchange, and captured in aMD (but absent in cMD) simulations, is a low-frequency motion intrinsic to the structure.
authors.affiliation: Department of Chemistry and Biochemistry and Center for Theoretical Biological Physics, University of California San Diego, La Jolla, California, United States of America. bgrant@mccammon.ucsd.edu
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Grant
authors.forename: Alemayehu A
authors.initials: AA
authors.lastname: Gorfe
authors.forename: J Andrew
authors.initials: JA
authors.lastname: McCammon
mesh_terms: D001665:Binding Sites; D003198:Computer Simulation; D004789:Enzyme Activation; D008956:Models, Chemical; D008958:Models, Molecular; D009711:Nucleotides / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D018631:ras Proteins / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D009711:Nucleotides; D018631:ras Proteins