Recombinant Cytochrome b559 subunit alpha (psbE)
Description
Role in PSII Assembly and Stability
PsbE is indispensable for the assembly of stable PSII reaction centers. Deletion mutants of psbE in Synechocystis sp. PCC 6803 and Chlamydomonas reinhardtii fail to accumulate functional PSII, leading to photoautotrophic growth defects .
Key Mechanisms:
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Structural Nucleation: PsbE interacts with D2 (PsbD) during early PSII assembly, forming a core complex essential for subsequent protein integration .
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Heme Coordination: Mutations disrupting His ligands (e.g., H23Aα in T. elongatus) destabilize the heme, but apoproteins (PsbE/PsbF without heme) still enable PSII assembly in thermophilic organisms .
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Electrostatic Interactions: Arg residues (e.g., R7α, R17α) in PsbE stabilize heme propionates via charge interactions, influencing redox properties .
Photoprotection and Redox Functions
PsbE contributes to secondary electron transfer pathways that mitigate photoinhibition:
Interactions with PsbP:
The N-terminal sequence of PsbP (pN15 peptide) binds PsbE, altering Cyt b559’s redox potential and oxygen-evolving activity. This interaction modulates electron flow and stabilizes the OEC .
Heme-Ligand Mutants
| Organism | Mutation | Phenotype |
|---|---|---|
| Synechocystis | R7Eα, R17Lβ | Slower growth, LP-form dominance, impaired photoprotection |
| T. elongatus | H23Aα, H23Mα | Apo-Cyt b559 assembled; stable PSII despite heme loss |
Gene Amplification in Cyanobacteria
In Synechocystis mutants with destabilized PsbE/PsbF, tandem repeats of the psbEFLJ operon restore PSII accumulation:
| Feature | Wild-Type | Mutant + Amplicon |
|---|---|---|
| psbEFLJ Copies | 1 | 5–15 |
| RNA Levels | Basal | 10–20× elevated |
| PSII Content | 100% | Recovered to ~80% |
This mechanism compensates for protein instability via overexpression .
Product Specs
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Target Background
This b-type cytochrome is integrally associated with the photosystem II (PSII) reaction center. PSII, a light-driven water:plastoquinone oxidoreductase, utilizes light energy to extract electrons from H₂O, producing O₂ and a proton gradient for subsequent ATP synthesis. It comprises a core antenna complex for photon capture and an electron transfer chain that converts photonic excitation into charge separation.
