Recombinant Cyanothece sp. Cytochrome b6-f complex subunit 4 (petD)
Description
Cytochrome b6-f Complex
The cytochrome b6-f complex is a protein complex that functions as a plastoquinol-plastocyanin oxidoreductase, mediating electron transport between Photosystem II (PSII) and Photosystem I (PSI) . It is involved in:
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Photosynthetic redox control of energy distribution between the two photosystems and gene expression
In cyanobacteria such as Cyanothece sp., and in plants, the cytochrome b6-f complex resides in thylakoid membranes .
petD Subunit
The petD subunit is one of the major subunits of the cytochrome b6-f complex . In M. laminosus, the cytochrome b6-f complex contains eight polypeptide subunits, including petA (cyt f), petB (cyt b6), petC (Rieske ISP), and petD (subunit IV) . The molecular weights of these subunits are 30.9, 24.7, 19.3, and 17.5 kDa, respectively, in spinach thylakoid membranes . The petD subunit corresponds to the C-terminal half of the cytochrome b subunit of the bc1 complex .
Structure and Function of the Cytochrome b6-f Complex
The cytochrome b6-f complex is a symmetric dimer with a molecular weight of approximately 220 kDa . Each monomer contains eight subunits, 13 trans-membrane helices, and seven prosthetic groups (four hemes, one [2Fe-2S] cluster, one chlorophyll a, and one β-carotene) . The core of the complex consists of the cytochrome b6 and subunit IV polypeptides .
Key features of the cytochrome b6-f complex include :
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An additional heme, cn, coupled closely and tightly to heme bn.
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Electron input into b6-f through ferredoxin and perhaps FNR.
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The position of the cyt f heme, on top of the elongate cyt f.
Recombinant petD
Recombinant petD is produced using genetic engineering techniques, where the gene encoding the petD subunit from Cyanothece sp. is expressed in a host organism like E. coli . The recombinant protein can then be purified and used for various research purposes .
Table 1: Properties of Recombinant Full Length Cyanothece sp. Cytochrome b6-f Complex Subunit 4(petD) Protein
| Property | Description |
|---|---|
| Source | E. coli |
| Tag | His |
| Protein Length | Full Length (1-160aa) |
| Form | Lyophilized powder |
| AA Sequence | MAVLKKPDLSDPKLRAKLAKGMGHNYYGEPAWPNDLLYVFPVVIMGTIGLVVGLAVLDPGMIGEPADPFATPLEILPEWYLYPVFQILRILPNKLLGIACQAAIPLGLMLIPFIESVNKFQNPFRRPVATTFFMIGTLVTLWLGAGAIFPIDKSLTLGLF |
| Purity | Greater than 90% as determined by SDS-PAGE |
| Storage | Store at -20°C/-80°C upon receipt, aliquoting is necessary for multiple uses. Avoid repeated freeze-thaw cycles. |
| Storage Buffer | Tris/PBS-based buffer, 6% Trehalose, pH 8.0 |
| Reconstitution | Reconstitute protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL. Add 5-50% of glycerol (final concentration). |
| Gene Name | petD |
| Synonyms | petD; PCC7424_2252; Cytochrome b6-f complex subunit 4; 17 kDa polypeptide |
| UniProt ID | B7KHH9 |
Product Specs
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Target Background
Recombinant Cyanothece sp. Cytochrome b6-f complex subunit 4 (petD) is a component of the cytochrome b6-f complex. This complex facilitates electron transfer between photosystem II (PSII) and photosystem I (PSI), cyclic electron flow around PSI, and state transitions.
KEGG: cyp:PCC8801_3537
STRING: 41431.PCC8801_3537
Q&A
Basic Research Questions
What methodologies are optimal for expressing and purifying recombinant PetD in heterologous systems?
Recombinant PetD is typically expressed in E. coli due to its tractability and scalability. Key steps include:
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Vector design: Use plasmids with inducible promoters (e.g., T7 or lacUV5) and affinity tags (e.g., N-terminal His-tag) for purification .
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Expression optimization: Test induction temperatures (e.g., 16–25°C) and IPTG concentrations to balance solubility and yield.
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Purification: Employ immobilized metal affinity chromatography (IMAC) followed by size-exclusion chromatography to ensure monodispersity .
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Storage: Stabilize purified protein in Tris-based buffers with 50% glycerol at -20°C or -80°C to prevent aggregation .
How can researchers confirm PetD’s functional role in the cytochrome b6f complex?
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Genetic knockout studies: In Synechocystis sp. PCC 6803, disruption of petD leads to merodiploid strains, indicating its essentiality for complex stability .
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Biochemical assays: Compare oxygen evolution rates in wild-type vs. ΔpetD mutants. A 70% reduction in activity was observed in Anabaena variabilis PetN-deficient mutants, reversible via TMPD-mediated electron bypass .
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Inhibitor sensitivity: Assess insensitivity to 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB), which targets cytochrome b6f .
Advanced Research Questions
How to resolve contradictions regarding cytochrome b6f’s role in cyanobacterial state transitions?
Studies conflict on whether cytochrome b6f is required for state transitions . Methodological approaches include:
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Comparative physiology: Test mutants (e.g., ΔpetD) under varying light conditions while monitoring PSI/PSII ratios via 77 K fluorescence .
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Redox profiling: Measure plastoquinone pool reduction states using spectrophotometry .
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Kinase activity assays: Investigate phosphorylation dynamics of light-harvesting complexes in ΔpetD backgrounds .
What strategies identify PetD’s interaction partners in photosynthetic membranes?
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Co-immunoprecipitation (Co-IP): Express FLAG-tagged PetD in Synechocystis sp. PCC 6803, immunoprecipitate under native conditions, and analyze bound proteins via mass spectrometry (MS) .
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Far-Western blotting: Use recombinant PetD-SUMO fusion proteins to probe membrane protein extracts for direct interactions .
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Crosslinking-MS: Apply chemical crosslinkers (e.g., DSS) to stabilize transient interactions in intact cells before MS analysis.
How can structural insights into PetD inform mutagenesis studies?
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Homology modeling: Leverage sequences from Cyanothece sp. (UniProt: B1WWL0) and Synechocystis (PetD: 17.5 kDa) to predict transmembrane helices and ligand-binding sites.
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Site-directed mutagenesis: Target conserved residues (e.g., MAIEKKPDLS motif in Cyanothece PetD ) to assess impacts on complex assembly using blue native PAGE.
What experimental designs address PetD’s essentiality in cyanobacteria?
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Conditional knockouts: Use copper-inducible promoters to regulate petD expression in Synechocystis .
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CRISPR interference (CRISPRi): Repress petD transcription via dCas9 and monitor photosynthetic phenotypes in real time .
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Complementation assays: Introduce petD orthologs from divergent species (e.g., Chlorella) to test functional conservation .
