6kif

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.

References

1. ↑ Park YI, Sandstrom S, Gustafsson P, Oquist G. Expression of the isiA gene is essential for the survival of the cyanobacterium Synechococcus sp. PCC 7942 by protecting photosystem II from excess light under iron limitation. Mol Microbiol. 1999 Apr;32(1):123-9. doi: 10.1046/j.1365-2958.1999.01332.x. PMID:10216865 doi:http://dx.doi.org/10.1046/j.1365-2958.1999.01332.x
2. ↑ Burnap RL, Troyan T, Sherman LA. The highly abundant chlorophyll-protein complex of iron-deficient Synechococcus sp. PCC7942 (CP43') is encoded by the isiA gene. Plant Physiol. 1993 Nov;103(3):893-902. doi: 10.1104/pp.103.3.893. PMID:8022940 doi:http://dx.doi.org/10.1104/pp.103.3.893
3. ↑ Sandstrom S, Park YI, Oquist G, Gustafsson P. CP43', the isiA gene product, functions as an excitation energy dissipator in the cyanobacterium Synechococcus sp. PCC 7942. Photochem Photobiol. 2001 Sep;74(3):431-7. doi:, 10.1562/0031-8655(2001)074<0431:ctigpf>2.0.co;2. PMID:11594057 doi:<0431:ctigpf>2.0.co;2 http://dx.doi.org/10.1562/0031-8655(2001)074<0431:ctigpf>2.0.co;2
4. ↑ Cao P, Cao D, Si L, Su X, Tian L, Chang W, Liu Z, Zhang X, Li M. Structural basis for energy and electron transfer of the photosystem I-IsiA-flavodoxin supercomplex. Nat Plants. 2020 Feb;6(2):167-176. doi: 10.1038/s41477-020-0593-7. Epub 2020 Feb , 10. PMID:32042157 doi:http://dx.doi.org/10.1038/s41477-020-0593-7