PsaL subunit is required for the formation of photosystem I trimers in the cyanobacterium Synechocystis sp. PCC 6803

Division of Biology, Kansas State University, Manhattan 66506-4901.
FEBS Letters (Impact Factor: 3.17). 01/1994; 336(2):330-4. DOI: 10.1016/0014-5793(93)80831-E
Source: PubMed


When membranes of the wild type strain of the cyanobacterium Synechocystis sp. PCC 6803 were solubilized with detergents and fractionated by sucrose-gradient ultracentrifugation, photosystem I could be obtained as trimers and monomers. We could not obtain trimers from the membranes of any mutant strain that lacked PsaL subunit. In contrast, absence of PsaE, PsaD, PsaF, or PsaJ did not completely abolish the ability of photosystem I to form trimers. Furthermore, PsaL is accessible to digestion by thermolysin in the monomers but not in the trimers of photosystem I purified from wild type membranes. Therefore, PsaL is necessary for trimerization of photosystem I and may constitute the trimer-forming domain in the structure of photosystem I.

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Available from: Parag R Chitnis, Mar 14, 2014
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    • "Unsolubilised membranes were removed by ultracentrifugation at 184,000×g for 30 min at 4°C. Supernatant corresponding to 0.5 mg Chl was applied to 5-step 10–30% sucrose gradients prepared as described by Chitnis and Chitnis (1993) [29]. The sucrose gradients were ultracentrifuged at 270,000×g for 21 hours at 4°C and green bands were carefully collected using a Pasteur pipette or 0.5 mL fractions were collected using a peristaltic pump. "
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    ABSTRACT: Plants produce an immense variety of specialized metabolites, many of which are of high value as their bioactive properties make them useful as for instance pharmaceuticals. The compounds are often produced at low levels in the plant, and due to their complex structures, chemical synthesis may not be feasible. Here, we take advantage of the reducing equivalents generated in photosynthesis in developing an approach for producing plant bioactive natural compounds in a photosynthetic microorganism by functionally coupling a biosynthetic enzyme to photosystem I. This enables driving of the enzymatic reactions with electrons extracted from the photosynthetic electron transport chain. As a proof of concept, we have genetically fused the soluble catalytic domain of the cytochrome P450 CYP79A1, originating from the endoplasmic reticulum membranes of Sorghum bicolor, to a photosystem I subunit in the cyanobacterium Synechococcus sp. PCC 7002, thereby targeting it to the thylakoids. The engineered enzyme showed light-driven activity both in vivo and in vitro, demonstrating the possibility to achieve light-driven biosynthesis of high-value plant specialized metabolites in cyanobacteria.
    PLoS ONE 07/2014; 9(7):e102184. DOI:10.1371/journal.pone.0102184 · 3.23 Impact Factor
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    • "Supporting this idea is the observation that cyanobacterial PSI trimers have been reported in almost every subclass of cyanobacteria. The most well characterized PSI trimers are from Synechocystis, Synechococcus, and Thermosynechococcus, where PsaL is needed for PSI trimerization in these cyanobacteria [94] [95] [96] [97]. In contrast, plant PSI is monomeric in the presence of PsaL, possibly due to interaction with the PsaH subunit that is not found in cyanobacteria [98] [99] [100]. "
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    ABSTRACT: Oxygenic photosynthesis is driven via sequential action of PSII and PSI reaction centers via the Z-scheme. Both of these pigment-membrane protein complexes are found in cyanobacteria, algae, and plants. Unlike PSII, PSI is remarkably stable and does not undergo limiting photo-damage. This stability, as well as other fundamental structural differences, makes PSI the most attractive reaction centers for applied photosynthetic applications. These applied applications exploit the efficient light harvesting and high quantum yield of PSI where the isolated PSI particles are redeployed providing electrons directly as a photocurrent or, via a coupled catalyst to yield H2. Recent advances in molecular genetics, synthetic biology, and nanotechnology have merged to allow PSI to be integrated into a myriad of biohybrid devices. In photocurrent producing devices, PSI has been immobilized onto various electrode substrates with a continuously evolving toolkit of strategies and novel reagents. However, these innovative yet highly variable designs make it difficult to identify the rate-limiting steps and/or components that function as bottlenecks in PSI-biohybrid devices. In this study we aim to highlight these recent advances with a focus on identifying the similarities and differences in electrode surfaces, immobilization/orientation strategies, and artificial redox mediators. Collectively this work has been able to maintain an annual increase in photocurrent density (A cm(-2)) of ~10-fold over the past decade. The potential drawbacks and attractive features of some of these schemes are also discussed with their feasibility on a large-scale. As an environmentally benign and renewable resource, PSI may provide a new sustainable source of bioenergy. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.
    Biochimica et Biophysica Acta 01/2014; 1837(9). DOI:10.1016/j.bbabio.2013.12.013 · 4.66 Impact Factor
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    • "Protein subunits of PS I were reduced about two-fold under low iron conditions (0.45), except PsaL, which was only found under iron limitation. In cyanobacteria, PsaL, generally important for trimer formation, facilitates the formation of IsiA (iron stress induced protein A) rings around PS I monomers under iron-deprivation [34]. We speculate that PsaL might be involved in the organization of PS I light-harvesting structures specifically formed under low-iron conditions and/or oligomerization of PS I in iron-limited T. oceanica. "
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    ABSTRACT: Background Biogeochemical elemental cycling is driven by primary production of biomass via phototrophic phytoplankton growth, with 40% of marine productivity being assigned to diatoms. Phytoplankton growth is widely limited by the availability of iron, an essential component of the photosynthetic apparatus. The oceanic diatom Thalassiosira oceanica shows a remarkable tolerance to low-iron conditions and was chosen as a model for deciphering the cellular response upon shortage of this essential micronutrient. Results The combined efforts in genomics, transcriptomics and proteomics reveal an unexpected metabolic flexibility in response to iron availability for T. oceanica CCMP1005. The complex response comprises cellular retrenchment as well as remodeling of bioenergetic pathways, where the abundance of iron-rich photosynthetic proteins is lowered, whereas iron-rich mitochondrial proteins are preserved. As a consequence of iron deprivation, the photosynthetic machinery undergoes a remodeling to adjust the light energy utilization with the overall decrease in photosynthetic electron transfer complexes. Conclusions Beneficial adaptations to low-iron environments include strategies to lower the cellular iron requirements and to enhance iron uptake. A novel contribution enhancing iron economy of phototrophic growth is observed with the iron-regulated substitution of three metal-containing fructose-bisphosphate aldolases involved in metabolic conversion of carbohydrates for enzymes that do not contain metals. Further, our data identify candidate components of a high-affinity iron-uptake system, with several of the involved genes and domains originating from duplication events. A high genomic plasticity, as seen from the fraction of genes acquired through horizontal gene transfer, provides the platform for these complex adaptations to a low-iron world.
    Genome biology 07/2012; 13(7):R66. DOI:10.1186/gb-2012-13-7-r66 · 10.81 Impact Factor
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