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AKB: Biologische Physik

AKB 55: Molecular Motors

AKB 55.3: Vortrag

Dienstag, 8. März 2005, 15:00–15:15, TU H2013

Molecular dynamics simulations of spontaneous and forced motions of isolated subunits of F₁-ATPase — •U. Kleinekathöfer¹, B. Isralewitz², M. Dittrich², and K. Schulten² — ¹Institut für Physik, Technische Universität Chemnitz, 09107 Chemnitz — ²Beckman Institute, University of Illinois, Urbana, USA.

The F₁ unit of ATP synthase converts a torque applied to its central stalk into chemical synthesis of ATP at binding sites nearly 100 Å away. F₁ has three-fold pseudo-symmetry, consisting of three non-catalytic α-subunits and three catalytic β-subunits. During synthesis, the torque-driven central stalk rotation causes the β-subunit to assume several different conformations at different points in the synthesis cycle. The reverse happens during hydrolysis: conformation changes in the β-subunits drive rotation of the central stalk. We examine the tendency towards spontaneous conformation change of isolated open, half-closed, and closed β- subunits of bovine mitochondrial F1-ATP synthase. In 10-ns molecular dynamics equilibrations, the subunit structural changes can be decomposed into two motions: one parallel to the pseudo-symmetry axis of F1 and one perpendicular to this axis. We also examine the behavior of the central stalk when a β-subunit is forced to close, simulating F1 functioning in hydrolysis mode. In a model system consisting of the central stalk and a single β- subunit, steered molecular dynamics transforms an isolated β-subunit from an half-closed state to a closed state, while the central stalk is constrained to rotate on the pseudo-symmetry axis. We describe how central stalk rotation proceeds as closing is enforced, and how several β-subunit structures effect the force transfer.