title: Paddling mechanism for the substrate translocation by AAA+ motor revealed by multiscale molecular simulations.
abstract: Hexameric ring-shaped AAA+ molecular motors have a key function of active translocation of a macromolecular chain through the central pore. By performing multiscale molecular dynamics (MD) simulations, we revealed that HslU, a AAA+ motor in a bacterial homologue of eukaryotic proteasome, translocates its substrate polypeptide via paddling mechanism during ATP-driven cyclic conformational changes. First, fully atomistic MD simulations showed that the HslU pore grips the threaded signal peptide by the highly conserved Tyr-91 and Val-92 firmly in the closed form and loosely in the open form of the HslU. The grip depended on the substrate sequence. These features were fed into a coarse-grained MD, and conformational transitions of HslU upon ATP cycles were simulated. The simulations exhibited stochastic unidirectional translocation of a polypeptide. This unidirectional translocation is attributed to paddling motions of Tyr-91s between the open and the closed forms: downward motions of Tyr-91s with gripping the substrate and upward motions with slipping on it. The paddling motions were caused by the difference between the characteristic time scales of the pore-radius change and the up-down displacements of Tyr-91s. Computational experiments on mutations at the pore and the substrate were in accord with several experiments.
authors.affiliation: Department of Biophysics, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Nobuyasu
authors.initials: N
authors.lastname: Koga
authors.forename: Tomoshi
authors.initials: T
authors.lastname: Kameda
authors.forename: Kei-ichi
authors.initials: K
authors.lastname: Okazaki
authors.forename: Shoji
authors.initials: S
authors.lastname: Takada
mesh_terms: D003198:Computer Simulation; D049071:Endopeptidase Clp / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D013379:Substrate Specificity
chemical_list: D049071:Endopeptidase Clp