Light harvesting protein B-800/850
Rhodopseudomonas acidophila (phototrophic bacteria)
Indirectly the sun is responsible for all life on earth. Life is a system of complex interacting processes and these processes consume energy. The energy in its chemical form comes from the conversion of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and phosphate (P), releasing the energy that is contained in this bond. Conversely ATP is made by fusing ADP and P to result in ATP. Since perpetuum mobiles do not exist, the energy for making ATP must come from somewhere else and the origin of this energy is the light from the sun. The process of converting the electromagnetic energy of the light to the chemical energy stored in the bonds of ATP is a process called photosynthesis. Photosynthesis is carried out by large protein complexes that are embedded in cell membranes. One part of this complex is responsible for the formation of ATP, other parts are responsible for capturing light. In some organisms photosystems combine both activities in the same complex, in others the processes are carried out by spatially separate proteins that are near each other in the cell membrane. The first structure of a membrane protein ever determined by crystallography was that of a bacterial reaction center where ATP is made. For this accomplishment Deisenhofer, Huber and Michel, three German scientists, received the 1988 Nobel prize in chemistry.
The structure here shows the light-harvesting complex of such a photosynthesis system. It acts as the antenna catching the solar photons. The basic building block is very simple: two helices, aligned parallel to each other. These basic building blocks assemble to larger aggregates. Associated with them are bacteriochlorophyll (BCL) pigment molecules. These are the molecules that absorb the photons. Six such pigments form a stack on one side of the molecule. Their tails extend into the inside of the molecule, where three more such pigment molecules, tilted roughly 90 degrees, sit. These two groups interact with each other through their long tails.
Protein Data Bank (PDB)
Prince, S.M. Papiz, M.Z. Freer, A.A. McDermott, G. Hawthornthwaite-Lawless, A.M. Cogdell, R.J. Isaacs, N.W.; "Apoprotein structure in the LH2 complex from Rhodopseudomonas acidophila strain 10050: modular assembly and protein pigment interactions."; J. Mol. Biol.; (1997) 268:412-423 PubMed:9159480.
author: Arno Paehler