Towards structural and functional characterization of photosynthetic and mitochondrial supercomplexes

Bioenergetic reactions in chloroplasts and mitochondria are catalyzed by large multi-subunit membrane proteins. About two decades ago it became clear that several of these large membrane proteins further associate into supercomplexes and since then a number of new ones have been described. In this review we focus on supercomplexes involved in light harvesting and electron transfer in the primary reactions of oxygenic photosynthesis and on the mitochondrial supercomplexes that catalyze electron transfer and ATP synthesis in oxidative phosphorylation. Functional and structural aspects are overviewed. In addition, several relevant technical aspects are discussed, including membrane solubilization with suitable detergents and methods of purification. Some open questions are addressed, such as the lack of high-resolution structures, the outstanding gaps in the knowledge about supercomplexes involved in cyclic electron transport in photosynthesis and the unusual mitochondrial protein complexes of protists and in particular of ciliates.