biostudies-literatureNagao RMEXT | Japan Society for the Promotion of ScienceJapan Agency for Medical Research and Development920https://www.ebi.ac.uk/biostudies/studies/S-EPMC9938196biostudies-literatureUnknown14(1)Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions. The cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, their binding property and functional roles in PSI are still missing. We analyzed a cryo-electron microscopy structure of a PSI-IsiA supercomplex isolated from Anabaena grown under an iron-deficient condition. The PSI-IsiA structure contains six IsiA subunits associated with the PsaA side of a PSI core monomer. Three of the six IsiA subunits were identified as IsiA1 and IsiA2. The PSI-IsiA structure lacks a PsaL subunit; instead, a C-terminal domain of IsiA2 occupies the position of PsaL, which inhibits the oligomerization of PSI, leading to the formation of a PSI monomer. Furthermore, excitation-energy transfer from INature communicationsStructure of a monomeric photosystem I core associated with iron-stress-induced-A proteins from Anabaena sp. PCC 7120.PMC9938196JP22H04916JP20K06528JP20H02914JP17H06434JP21K19085Tsuboshita NSuzuki TUeno YKawakami KShimizu SEhira SDohmae NFurutani MNakajima YAkimoto SNagao RKato KShen JRHamaguchi TYonekura KfalseStructure of a monomeric photosystem I core associated with iron-stress-induced-A proteins from Anabaena sp. PCC 7120.Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions. The cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, their binding property and functional roles in PSI are still missing. We analyzed a cryo-electron microscopy structure of a PSI-IsiA supercomplex isolated from Anabaena grown under an iron-deficient condition. The PSI-IsiA structure contains six IsiA subunits associated with the PsaA side of a PSI core monomer. Three of the six IsiA subunits were identified as IsiA1 and IsiA2. The PSI-IsiA structure lacks a PsaL subunit; instead, a C-terminal domain of IsiA2 occupies the position of PsaL, which inhibits the oligomerization of PSI, leading to the formation of a PSI monomer. Furthermore, excitation-energy transfer from I2023-01-01T00:00:00Z2023 Feb2026-05-28T16:36:48.586Z2024-10-15T05:17:50.209ZS-EPMC99381963680559810.1038/s41467-023-36504-1