Partial symmetrization of the photosynthetic reaction center.
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 alpha helices and pigments are arranged in an approximate C2 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.
Graduate Program in Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge 02139.
S J
SJ
Robles
J
J
Breton
D C
DC
Youvan
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D003001:Cloning, Molecular; D004579:Electron Transport; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D011487:Protein Conformation; D012241:Rhodopseudomonas / Q000032:analysis / Q000235:genetics / Q000254:growth & development; D013053:Spectrophotometry
D001426:Bacterial Proteins; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins