Colloidal aspects of photosynthetic membrane proteins

Light-harvesting and reaction center complexes are large transmembrane pigment–protein complexes that play a fundamental role in photosynthesis. Their study is a frontier area of biological energy- and electron-transfer. Suitable detergents are required to solubilize photosynthetic membrane proteins. Actually a solution of these photosynthetic proteins consist of an ensemble of protein–detergent complexes often polydisperse in composition because surfactants, lipids and hydrophobic cofactors (e.g. quinones) are non-homogeneously distributed. Here I describe how knowledge and concepts coming from colloid science and soft matter physics are required to fully understand the behaviour of photosynthetic membrane proteins. The topics covered include solution properties, surfactant–protein interactions, heterogeneity effects, and slow protein dynamics.