Regensburg 2004 – wissenschaftliches Programm

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SYLS: Life Sciences on the Nanometer Scale - Physics Meets Biology

SYLS 5: Symposium "Life Sciences on the Nanometer Scale - Physics Meets Biology"

SYLS 5.3: Vortrag

Donnerstag, 11. März 2004, 12:00–12:15, H 37

Molecular dynamics simulations of isolated β-subunits of F₁-ATPase — •U. Kleinekathöfer¹, B. Isralewitz², M. Dittrich², and K. Schulten² — ¹International University Bremen, 28725 Bremen — ²Beckman Institute, University of Illinois, Urbana-Champaign, USA.

The F₁ unit of ATPase has three-fold symmetry and consists of three noncatalytic α and three catalytic β-subunits. The β-subunits furnish the binding sites where ADP is transformed into ATP. We have investigated the properties of isolated β-subunits as a step towards explaining the function of the integral F₁ unit. The β-subunits exist in different conformations at any moment of the F₁ unit reaction cycle.

The open conformation of the AlF₃-inhibited β-subunit of bovine ATPase had been equilibrated for about 10 ns and a spontaneous change in conformation was observed. The change can be decomposed into two rotations: one around an axis parallel to the pseudo-symmetry axis of F₁-ATPase and one around an axis perpendicular to the first axis . In several runs the equilibrated subunit was in a conformation about half-way between the open and the closed conformation. This partially confirms the assumption that elastic energy is stored in the open confirmation. It is unclear if there is a further spontaneous closing motion on longer time scales. To test the effect of the adjacent alpha subunit we performed simulations of the joined units and found only a negligible effect. We also equilibrated isolated β-subunits for the AlF₄⁻-inhibited F₁-ATPase starting from the the half-closed state with ADP bound and from modified half-closed states with bound ATP. The simulations again revealed spontaneous motion towards the closed conformation.