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

Abstract

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.

A Bacterial Multidomain NAD-Independent d -Lactate Dehydrogenase Utilizes Flavin Adenine Dinucleotide and Fe-S Clusters as Cofactors and Quinone as an Electron Acceptor for d -Lactate Oxidization

“…Another feature of Fe-S proteins is that they are often linked to biomembranes (55)(56)(57). Fe-S D-iLDH has been previously identified as a membrane-associated enzyme (34), but no possible transmembrane helix was predicted for the whole Fe-S D-iLDH (http://www.ch.embnet.org/software/TMPRED_form.html).…”

Effects of Light and Oxygen on Chlorophyll d Biosynthesis in a Marine Cyanobacterium Acaryochloris marina

“…Through the analysis of the glucose transporter GlcP and the glucokinase (glk), the accumulation of unmetabolized glucose in the cells caused the growth defect [ 13 ]. Additionally, it has been reported that the loss of FesM, a protein involved in PSI cyclic electron transfer, in Synechococcus sp PCC 7002 prevents mixotrophic growth using glycerol, suggesting that the addition of glycerol affects the reduction state of the PQ pool, leading to poor growth [ 14 ]. In this experiment, the growth of Acaryochloris species was inhibited by the addition of glycerol, sucrose, and glucose, suggesting that the influx of reducing power from these exogenous carbon sources affects the reduction state of the PQ pool, which resulted in inhibited growth ( Figure 2 ).…”

Significant energy transfer from CpcG2‐phycobilisomes to photosystem I in the cyanobacterium Synechococcus sp. PCC 7002 in the absence of ApcD‐dependent state transitions

“…Fluorescence emission spectra at 77 K were measured according to Zhao et al [17]. Thylakoid membranes were isolated based on the phase partition method [18] which was modified according Xu et al [19]. Detection of GFP with immunoblotting was performed according Zhao et al [20].…”