Molecular organizations and function of iron-stress-induced-a protein family in Anabaena sp. PCC 7120.

Nagao, Ryo; Yokono, Makio; Ueno, Yoshifumi; Suzuki, Takehiro; Kato, Koji; Kato, Ka-Ho; Tsuboshita, Naoki; Jiang, Tian-Yi; Dohmae, Naoshi; Shen, Jian-Ren; Ehira, Shigeki; Akimoto, Seiji

Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions, and surround photosystem I (PSI) trimer with a ring formation. A cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, it is unknown how the IsiAs are associated with PSI. Here we report on molecular organizations and function of the IsiAs in this cyanobacterium. A deletion mutant of the isiA1 gene was constructed, and the four types of thylakoids were prepared from the wild-type (WT) and ΔisiA1 cells under iron-replete (+Fe) and iron-deficient (Fe) conditions. Immunoblotting analysis exhibits a clear expression of the IsiA1 in the WT - Fe. The PSI-IsiA1 supercomplex is found in the WT - Fe, and excitation-energy transfer from IsiA1 to PSI is verified by time-resolved fluorescence analyses. Instead of the IsiA1, both IsiA2 and IsiA3 are bound to PSI monomer in the ΔisiA1 - Fe. These findings provide insights into multiple-expression system of the IsiA family in this cyanobacterium.