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The PSI1-IsiA13 complex with double-layered IsiA proteins bound to the monomeric PSI core
Structural highlights
FunctionISIA_THEVB Functions as an antenna for photosystem I (PSI) under iron-limiting conditions, when phycobilisomes disappear. In the (PSI)3(Isi3)18 complex most of the harvested energy is probably used by PSI; in other PSI-containing supercomplexes a large part of the energy will probably not be used for light harvesting, but rather is dissipated to protect the organism from light damage.[UniProtKB:Q55274] Publication Abstract from PubMedIron-limitation is a common stress factor in natural environments. To survive under iron-starved conditions, cyanobacteria overexpress iron stress-induced protein A (IsiA), which is crucial for light-harvesting and photoprotection. Multiple IsiA proteins form a single- or double-layered architecture encircling the photosystem I (PSI) core, forming various PSI-IsiA supercomplexes. The assembly and energy transfer mechanisms of double-layered PSI-IsiA supercomplexes remain unelucidated. Here, we present high-resolution structures of two PSI-IsiA supercomplexes isolated from the cyanobacterium Thermosynechococcus elongatus BP-1 cultured under iron-starved conditions. The PSI(3)-IsiA(43) complex contains a trimeric PSI core surrounded by 43 IsiA subunits assembled into a closed double-ring. The PSI(1)-IsiA(13) complex contains 13 IsiA proteins arranged in a double-layered architecture attached to the monomeric PSI core. Atomic force microscopy demonstrates the presence and distribution of different PSI-IsiA complexes within native thylakoid membranes isolated from iron-starved cells. Our findings provide insights into the structural variability and adaptive mechanisms of PSI-IsiA complexes. Structural basis for the assembly and energy transfer between the cyanobacterial PSI core and the double-layered IsiA proteins.,Si L, Zhang Y, Su X, Zhao X, An X, Liu LN, Cao P, Li M Nat Commun. 2025 Dec 20. doi: 10.1038/s41467-025-67295-2. PMID:41422266[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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