Investigation of photosynthetic membrane structure using atomic force microscopy

International audiencePhotosynthetic processes, including light capture, electron transfer, and energy conversion, are not only ensured by the activities of individual photosynthetic complexes but also substantially determined and regulated by the composition and assembly of the overall photosynthetic apparatus at the supramolecular level. In recent years, atomic force microscopy (AFM) has matured as a unique and powerful tool for directly assessing the supramolecular assembly of integral membrane protein complexes in their native membrane environment at submolecular resolution. This review highlights the major contributions and advances of AFM studies to our understanding of the structure of the bacterial pho-tosynthetic machinery and its regulatory arrangement during chromatic adaptation. AFM topographs of other biological membrane systems and potential future applications of AFM are also discussed. Bacterial photosynthetic apparatus Photosynthesis, performed by green plants, algae, and some bacteria, is the major source of energy on the planet. Today, it is rationalised that important lessons can be learned from nature concerning the capture and conversion of abundant solar energy for the development of renewable energy resources. Ideas comprise the use of natural photosynthesis for biofuel generation, devices that partially consist of biological materials, or bio-inspired technology. In all cases, a profound knowledge of how nature designed photosynthetic machineries is a prerequisite for developments. Indeed, through photosynthesis carried out in specialised membrane systems – the photo-synthetic membranes – all green plants, algae, and some bacteria can convert solar radiant energy with high efficiency into chemical energy [1,2]. This energy is then used to power cellular metabolisms. The purple bacterial pho-tosynthetic membranes are intracytoplasmic membranes (ICMs, see Glossary, sometimes also termed chromato-phore), where absorption and conversion of light energy is efficiently accomplished by a multicomponent assembly of pigment–protein photosynthetic complexes. These complexes include light-harvesting complexes (LH2 and LH1) and reaction centres (RCs), which together form the pho-tosynthetic unit (PSU), cytochrome (cyt) bc 1 complexes, and ATP synthases (ATPases) [3]. The physiological arrangement and strong cooperation of these protein constituents are fundamental to efficient light capture and energy transfer mechanisms