FesM, a membrane iron-sulfur protein, is required for cyclic electron flow around photosystem I and photoheterotrophic growth of the cyanobacterium Synechococcus sp. PCC 7002.
While it is known that cyclic electron flow around photosystem I is an important pathway of photosynthetic electron transfer for converting light energy to chemical energy, some components of cyclic electron flow remain to be revealed. Here, we show that fesM, encoding a novel membrane iron-sulfur protein, is essential to cyclic electron flow in the cyanobacterium Synechococcus sp. PCC 7002. The FesM protein is predicted to have a cAMP-binding domain, an NtrC-like domain, a redox sensor motif, and an iron-sulfur (4Fe-4S) motif. Deletion of fesM (fesM-D) led to an inability for Synechococcus cells to grow in the presences of glycerol and 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Photoheterotrophic growth was restored by a complete fesM gene present on a replicable plasmid. A mutant fesM gene encoding a truncated FesM protein lacking the cAMP domain failed to restore the phenotype, suggesting this domain is important to the function of FesM. Measurements of reduction of P700(+) and the redox state of interphotosystem electron carriers showed that cells had a slower rate of respiratory electron donation to the interphotosystem electron transport chain, and cyclic electron flow around photosystem I in fesM-D was impaired, suggesting that FesM is a critical protein for respiratory and cyclic electron flow. Phosphatase fusion analysis showed that FesM contains nine membrane-spanning helices, and all functional domains of FesM are located on the cytoplasmic face of the thylakoid membranes.
Xu
Dongyi
D
State Key Laboratory of Protein and Genetic Engineering, College of Life Science, Peking University, Beijing 100871, China.
Liu
Xianwei
X
Zhao
Jiao
J
Zhao
Jindong
J
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004579:Electron Transport; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008027:Light; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D046939:Synechocystis / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects
D001426:Bacterial Proteins; D017931:DNA Primers; D007506:Iron-Sulfur Proteins; D008565:Membrane Proteins; D045331:Photosystem I Protein Complex