Electron Conduction and Photocurrent Generation of a Light-Harvesting/Reaction Center Core Complex in Lipid Membrane Environments

To reveal the structure–function relationship of membrane proteins, a membrane environment is often used to establish a suitable platform for assembly, functioning, and measurements. The control of the orientation of membrane proteins is the main challenge. In this study, the electron conductivity and photocurrent of a light-harvesting/reaction center core complex (LH1-RC) embedded in a lipid membrane were measured using conductive atomic force microscopy (C-AFM) and photoelectrochemical analysis. AFM topographs showed that LH1-RC molecules were well-orientated, with their H-subunits toward the membrane surface. Rectified conductivity was observed in LH1-RC under precise control of the applied force on the probe electrode (<600 pN). LH1-RC embedded in a membrane generated photocurrent upon irradiation when assembled on an electrode. The observed action spectrum was consistent with the absorption spectrum of LH1-RC. The control of the orientation of LH1-RC by lipid membranes provided well-defined conductivity and photocurrent

Construction and Structural Analysis of Tethered Lipid Bilayer Containing Photosynthetic Antenna Proteins for Functional Analysis

The construction and structural analysis of a tethered planar lipid bilayer containing bacterial photosynthetic membrane proteins, light-harvesting complex 2 (LH2), and light-harvesting core complex (LH1-RC) is described and establishes this system as an experimental platform for their functional analysis. The planar lipid bilayer containing LH2 and/or LH1-RC complexes was successfully formed on an avidin-immobilized coverglass via an avidin–biotin linkage. Atomic force microscopy (AFM) showed that a smooth continuous membrane was formed there. Lateral diffusion of these membrane proteins, observed by a fluorescence recovery after photobleaching (FRAP), is discussed in terms of the membrane architecture. Energy transfer from LH2 to LH1-RC within the tethered membrane was observed by steady-state fluorescence spectroscopy, indicating that the tethered membrane can mimic the natural situation