6kif
From Proteopedia
Structure of cyanobacterial photosystem I-IsiA-flavodoxin supercomplex
Structural highlights
Function[PSAC_SYNE7] Apoprotein for the two 4Fe-4S centers FA and FB of photosystem I (PSI); essential for photochemical activity. FB is the terminal electron acceptor of PSI, donating electrons to ferredoxin. The C-terminus interacts with PsaA/B/D and helps assemble the protein into the PSI complex. Required for binding of PsaD and PsaE to PSI. PSI is a plastocyanin/cytochrome c6-ferredoxin oxidoreductase, converting photonic excitation into a charge separation, which transfers an electron from the donor P700 chlorophyll pair to the spectroscopically characterized acceptors A0, A1, FX, FA and FB in turn.[HAMAP-Rule:MF_01303] [FLAV_SYNE7] Low-potential electron donor to a number of redox enzymes. [PSAB_SYNE7] PsaA and PsaB bind P700, the primary electron donor of photosystem I (PSI), as well as the electron acceptors A0, A1 and FX. PSI is a plastocyanin/cytochrome c6-ferredoxin oxidoreductase, converting photonic excitation into a charge separation, which transfers an electron from the donor P700 chlorophyll pair to the spectroscopically characterized acceptors A0, A1, FX, FA and FB in turn. Oxidized P700 is reduced on the lumenal side of the thylakoid membrane by plastocyanin or cytochrome c6. [PSAJ_SYNE7] May help in the organization of the PsaE and PsaF subunits.[HAMAP-Rule:MF_00522] [PSAA_SYNE7] PsaA and PsaB bind P700, the primary electron donor of photosystem I (PSI), as well as the electron acceptors A0, A1 and FX. PSI is a plastocyanin/cytochrome c6-ferredoxin oxidoreductase, converting photonic excitation into a charge separation, which transfers an electron from the donor P700 chlorophyll pair to the spectroscopically characterized acceptors A0, A1, FX, FA and FB in turn. Oxidized P700 is reduced on the lumenal side of the thylakoid membrane by plastocyanin or cytochrome c6. [ISIA_SYNE7] Functions as an antenna for photosystem I (PSI) under iron-limiting conditions, when phycobilisomes disappear. Also functions as a dissipator of light energy, protecting cells from excessive light under iron-deficient conditions. Sequesters chlorophyll when cells are growing in iron-deficient conditions; it may bind up to 50% of the chlorophyll in iron-starved cells.[1] [2] [3] [PSAE_SYNE7] Stabilizes the interaction between PsaC and the PSI core, assists the docking of the ferredoxin to PSI and interacts with ferredoxin-NADP oxidoreductase. Publication Abstract from PubMedUnder iron-deficiency stress, which occurs frequently in natural aquatic environments, cyanobacteria reduce the amount of iron-enriched proteins, including photosystem I (PSI) and ferredoxin (Fd), and upregulate the expression of iron-stress-induced proteins A and B (IsiA and flavodoxin (Fld)). Multiple IsiAs function as the peripheral antennae that encircle the PSI core, whereas Fld replaces Fd as the electron receptor of PSI. Here, we report the structures of the PSI3-IsiA18-Fld3 and PSI3-IsiA18 supercomplexes from Synechococcus sp. PCC 7942, revealing features that are different from the previously reported PSI structures, and a sophisticated pigment network that involves previously unobserved pigment molecules. Spectroscopic results demonstrated that IsiAs are efficient light harvesters for PSI. Three Flds bind symmetrically to the trimeric PSI core-we reveal the detailed interaction and the electron transport path between PSI and Fld. Our results provide a structural basis for understanding the mechanisms of light harvesting, energy transfer and electron transport of cyanobacterial PSI under stressed conditions. Structural basis for energy and electron transfer of the photosystem I-IsiA-flavodoxin supercomplex.,Cao P, Cao D, Si L, Su X, Tian L, Chang W, Liu Z, Zhang X, Li M Nat Plants. 2020 Feb;6(2):167-176. doi: 10.1038/s41477-020-0593-7. Epub 2020 Feb , 10. PMID:32042157[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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