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
Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
Institute of Low Temperature Science, Hokkaido University, Hokkaido 060-0819, Japan.
Biochim Biophys Acta Bioenerg. 2021 Jan 1;1862(1):148327. doi: 10.1016/j.bbabio.2020.148327. Epub 2020 Oct 15.
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.
铁胁迫诱导蛋白（IsiAs）在缺铁条件下于蓝藻中表达，并以环状结构围绕光系统I（PSI）三聚体。蓝藻鱼腥藻Anabaena sp. PCC 7120有四个isiA基因；然而，尚不清楚IsiAs如何与PSI相关联。在此，我们报道了该蓝藻中IsiAs的分子组织和功能。构建了isiA1基因的缺失突变体，并在铁充足（+Fe）和缺铁（-Fe）条件下从野生型（WT）和ΔisiA1细胞中制备了四种类囊体。免疫印迹分析显示WT-Fe中IsiA1有明显表达。在WT-Fe中发现了PSI-IsiA1超复合物，并且通过时间分辨荧光分析证实了从IsiA1到PSI的激发能转移。在ΔisiA1-Fe中，IsiA2和IsiA3均与PSI单体结合，而不是IsiA1。这些发现为该蓝藻中IsiA家族的多重表达系统提供了见解。
