Analysis of the elementary processes in the light-driven Cl- pump of halorhodopsin

点击翻译按钮获取中文摘要

Halorhodopsin (HR) is an inward light-driven Cl- pump in the membrane of halophilic archaea. Illumination triggers the photoreaction of HR called photocycle where the intermediates of K, L1, L2, N, O, NpHR' form and decay sequentially. During this cyclic reaction, HR releases Cl- to the cytoplasmic (CP) medium and captures another Cl- from the extracellular medium. To examine the elementary processes for Cl- translocation, we analyzed the photocycle using the flash-photolysis technique and obtained the following results: 1) Cl- release and uptake occur during N to O and O to NpHR' transitions, respectively. The subsequent NpHR' to original NpHR transition involves Cl- displacement inside the protein. 2) The Cl- binding affinity decreases at the Cl- releasing step. This decreased binding affinity contributes to maintain the Cl- pumping activity even in the presence of the interior negative membrane potential.