Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530, Japan.
Faculty of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan.
Nat Commun. 2023 Feb 17;14(1):920. doi: 10.1038/s41467-023-36504-1.
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 IsiAs to PSI appeared with a time constant of 55 ps. These findings provide insights into both the molecular assembly of the Anabaena IsiA family and the functional roles of IsiAs.
缺铁条件下，蓝细菌中会表达铁胁迫诱导的 A 蛋白（IsiAs）。鱼腥藻 PCC 7120 有四个 isiA 基因；然而，它们在 PSI 中的结合特性和功能作用仍不清楚。我们分析了在缺铁条件下生长的鱼腥藻中分离出的 PSI-IsiA 超复合体的低温电子显微镜结构。PSI-IsiA 结构包含六个与 PSI 核心单体 PsaA 侧结合的 IsiA 亚基。这六个 IsiA 亚基中的三个被鉴定为 IsiA1 和 IsiA2。PSI-IsiA 结构缺少 PsaL 亚基；相反，IsiA2 的 C 末端结构域占据了 PsaL 的位置，抑制了 PSI 的寡聚化，导致 PSI 单体的形成。此外，从 IsiAs 到 PSI 的能量转移出现了 55 ps 的时间常数。这些发现为鱼腥藻 IsiA 家族的分子组装和 IsiAs 的功能作用提供了深入了解。
