Chlorophyll‐binding Proteins

Chlorophylls and bacteriochlorophylls are the dominant pigments on Earth and serve – noncovalently bound to specific proteins – as principal light-harvesting as well as energy-transforming cofactors in photosynthetic organisms. The major groups of (bacterio)chlorophyll-binding proteins are the photosynthetic reaction centres (RCs) and the associated light-harvesting (antenna) complexes. Other proteins include water-soluble chlorophyll-binding proteins as well the chlorophyll biosynthetic and degrading enzymes. Although all RCs show structural homologies and appear to have evolved from a common ancestor, light-harvesting antenna designs vary considerably. The enormous progress that has been achieved in the elucidation of structures and functions of chlorophyll-binding proteins is reviewed. It has become increasingly clear that light-harvesting complexes do not only serve to enlarge the absorption cross-sections of the RCs but are important in the adaptation of the photosynthetic apparatus and regulation of the energy-transforming processes in response to environmental and endogenous conditions. Key Concepts: Chlorophylls and bacteriochlorophylls serve – noncovalently bound to specific proteins – as principal energy-transforming cofactors in photosynthesis. Light-harvesting antenna complexes ensure optimised light harvesting and transfer of excitation energy to the reaction centres of the photosystems. Reaction centre proteins remained fairly conserved during evolution, whereas photosynthetic organisms developed many distinct forms of light-harvesting complexes. Oxygenic photosynthesis evolved to two different photosystems that have most likely emerged from a common ancestor. The antenna system of plants and algae can ‘switch’ from effective light harvesting to photoprotective excess excitation dissipation to prevent photo-oxidative damage. Keywords: bacteriochlorophylls; chlorophylls; light-harvesting complexes; photosynthesis; pigment–protein complexes; reaction centres; electron transport; photosystems; photoprotection; nonphotochemical quenching