Role of the Longest Arm of Phycobilisome Core-Membrane Linker in Assembling the Phycobilisomes From Synechocystis sp. PCC 6803
Year: 2025
Type: article
Abstract: Background: The phycobilisomes (PBS) of cyanobacteria and red algae are unique light-harvesting protein-pigment complexes that utilize bilin derivatives for light absorption and energy transfer. These extramembranous mega-Dalton complexes are specifically organized and anchored to photosystem II (PSII) via the multi-domain core-membrane linker (LCM). While Arm2 is the longest segment in LCM domain, its specific functions remain uncharacterized. Methods: A series of Synechocystis sp. PCC 6803 mutants with complete or partial deletions of Arm2 and its adjacent Rep domains within LCM were constructed. The assembled PBSs were isolatedand characterized using sucrose gradient ultracentrifugation, absorption and fluorescence spectroscopy, and SDS-PAGE. Physiological functions were further assessed by analyzing growth, photosynthetic performance, state transitions, and non-photochemical quenching (NPQ). Results: Our results reveal that the super-secondary element of helix-turn-helix of Arm2 is critical for assembling the two longitudinal halves of PBS. The truncation of either or both helices of Arm2 results in the specific degradation of the longitudinal half harboring the terminal emitter, ApcD. Consequently, these mutants were deficient in state transitions and exhibited accelerated recovery from orange carotenoid protein (OCP)-mediated NPQ. We also identified the Arm2(37–67) motif likely involved in attaching the rods to the core, whereas the Arm2(68–129) region had no significant impact on PBS assembly. Conclusions: The helix-loop-helix element of Arm2 is essential for the longitudinal integrity of the PBS core and is a prerequisite for state transitions. These results suggest that state transitions may involve longitudinal rearrangements within the PBS structure, rather than lateral movements of the two halves, implicating that state transitions result from the longitudinal instead of the lateral moves of the two halves of the PBSs.
Source: Frontiers in Bioscience-Landmark
DOI: 10.31083/fbl47370
Authors: Nannan Niu, Ning Chen, Huanhuan Feng, Xueli Du
Institution: Luoyang Polytechnic
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $2,500
OpenAlex ID: W7117685083