Partial Symmetrization of the Photosynthetic Reaction Center

• Published in: Science (American Association for the Advancement of Science) 1990-06, Vol.248 (4961), p.1402-1405
• Main Authors: Robles, Steven J., Breton, Jacques, Youvan, Douglas C.
• Format: Article
• Language: English
• Subjects: 140505 - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-); Absorption spectra; Amino Acid Sequence; Amino acid sequencing; Amino acids; Analysis; Bacteria, Photosynthetic; Bacterial Proteins - genetics; Bacteriochlorophylls; Biological and medical sciences; Charge separation; CHEMICAL REACTIONS; Cloning, Molecular; DATA; Electron transfer; Electron Transport; Electrons; EXPERIMENTAL DATA; Fundamental and applied biological sciences. Psychology; Genetic mutation; Genetics; INFORMATION; KINETICS; Macromolecular Substances; Membrane proteins; Molecular biophysics; Molecular Sequence Data; Molecular Structure; Molecules; Mutation; NUMERICAL DATA; ORGANIC COMPOUNDS; PEPTIDES; PHOTOCHEMICAL REACTIONS; PHOTOSYNTHESIS; Photosynthetic bacteria; Photosynthetic Reaction Center Complex Proteins; Pigments; Protein Conformation; PROTEINS; Quinones; REACTION KINETICS; Rhodopseudomonas - analysis; Rhodopseudomonas - genetics; Rhodopseudomonas - growth & development; SOLAR ENERGY; Spectrophotometry; Structure in molecular biology; SYNTHESIS; Tridimensional structure
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.2192455

The bacterial photosynthetic reaction center (RC) is a pigmented intrinsic membrane protein that performs the primary charge separation event of photosynthesis, thereby converting light to chemical energy. The RC pigments are bound primarily by two homologous Peptides, the L and M subunits, each containing five transmembrane helices. These α helices and pigments are arranged in an approximate C$_2$ symmetry and form two possible electron transfer pathways. Only one of these pathways is actually used. In an attempt to identify nonhomologous residues that are responsible for functional differences between the two branches, homologous helical regions that interact extensively with the pigments were genetically symmetrized (that is, exchanged). For example, replacement of the fourth transmembrane helix (D helix) in the M subunit with the homologous helix from the L subunit yields photosynthetically inactive RCs lacking a critical photoactive pigment. Photosynthetic revertants have been isolated in which single amino acid substitutions (intragenic suppressors) compensate for this partial symmetrization.