Biology subjects

Cupellini, L.

Publications and source records attributed to Cupellini, L..

4 recordsLinked to original sources

bioRxiv2025

Structural determinants for red-shifted absorption in higher-plants Photosystem I

- Higher plants Photosystem I absorbs near-infrared light through long-wavelength chlorophylls, enriched under vegetation canopies, to enhance photon capture. Far-red absorption originates from chlorophylls pairs within the Lhca3 and Lhca4 subunits of the LHCI antenna, known as the "red cluster" composed of chlorophylls a603 and a609. - We used reverse genetics to produce an Arabidopsis mutant devoid of red-shifted absorption, and we obtained high-resolution cryo-EM structures from purified PSI-LHCI complexes in both wild-type and mutant plants. - Computed excitonic coupling values suggested a possible contribution of additional nearby pigment molecules, namely chlorophyll a615 and violaxanthin in L2 site, to far-red absorption. Therefore, we investigated the structural determinants of far-red absorption and analyzed the spectroscopic effects of these additional pigments by producing further Arabidopsis transgenic lines. The two experimental structures were used for quantum mechanics calculations, revealing that excitonic interactions alone cannot explain far-red absorption, while charge transfer states were needed for accurate spectral simulations. - Our findings demonstrate that the molecular mechanisms of light-harvesting under shaded conditions rely on very precise tuning of chromophore interactions, an understanding of which is crucial for designing light-harvesting complexes with engineered absorption spectra

plant biology↗

bioRxiv2023

Structural and quantum chemical basis for OCP-mediated quenching of phycobilisomes

Cyanobacteria employ large antenna complexes called phycobilisomes (PBS) for light harvesting. However, intense light triggers non-photochemical quenching, where the Orange Carotenoid Protein (OCP) binds to PBS, dissipating excess energy as heat. The mechanism of efficiently transferring energy from phycocyanobilins in PBS to canthaxanthin in OCP remains insufficiently understood. Using advanced cryogenic-electron microscopy, we unveiled the OCP-PBS complex structure at 1.6-2.1 [A] resolution, showcasing its inherent flexibility. Employing multiscale quantum chemistry, we disclosed the quenching mechanism. Identifying key protein residues, we clarified how canthaxanthins transition dipole moment in its lowest-energy dark state becomes large enough for efficient energy transfer from phycocyanobilins. Our energy transfer model offers a detailed understanding of the atomic determinants of light harvesting regulation and antenna architecture in cyanobacteria. One sentence summaryHigh-resolution cryo-EM structure of the OCP-PBS complex reveals intrinsic motions and enables the atomic simulation of the quenching mechanism

biophysics↗

bioRxiv2022

Quantum chemical elucidation of a sevenfold symmetric bacterial antenna complex

The light-harvesting complex 2 (LH2) of purple bacteria is one of the most studied photosynthetic antenna complexes. Its symmetric structure and ring-like bacteriochlorophyll arrangement make it an ideal system for theoreticians and spectroscopists. LH2 complexes from most bacterial species are thought to have eightfold or ninefold symmetry, but recently a sevenfold symmetric LH2 structure from the bacterium Mch. purpuratum was solved by Cryo-Electron microscopy. This LH2 also possesses unique nearinfrared absorption and circular dichroism (CD) spectral properties. Here we use an atomistic strategy to elucidate the spectral properties of Mch. purpuratum LH2 and understand the differences with the most commonly studied LH2 from Rbl. acidophilus. Our strategy exploits a combination of molecular dynamics simulations, multiscale polarizable quantum mechanics/molecular mechanics calculations, and lineshape simulations. Our calculations reveal that the spectral properties of LH2 complexes are tuned by site energies and exciton couplings, which in turn depend on the structural fluctuations of the bacteriochlorophylls. Our strategy proves effective in reproducing the absorption and CD spectra of the two LH2 complexes, and in uncovering the origin of their differences. This work proves that it is possible to obtain insight into the spectral tuning strategies of purple bacteria by quantitatively simulating the spectral properties of their antenna complexes.

biophysics↗

bioRxiv2021

Structure of the stress-related LHCSR1 complex determined by an integrated computational strategy

Light-harvesting complexes (LHCs) are pigment-protein complexes whose main function is to capture sunlight and transfer the energy to reaction centers of photosystems. In response to varying light conditions, LH complexes also play photoregulation and photoprotection roles. In algae and mosses, a sub-family of LHCs, Light-Harvesting complex stress related (LHCSR), is responsible for photoprotective quenching. Despite their functional and evolutionary importance, no direct structural information on LHCSRs is available that can explain their unique properties. In this work we propose a structural model of LHCSR1 from the moss P. Patens, obtained through an integrated computational strategy that combines homology modeling, molecular dynamics, and multiscale quantum chemical calculations. The model is validated by reproducing the spectral properties of LHCSR1. Our model reveals the structural specificity of LHCSR1, as compared with the CP29 LH complex, and poses the basis for understanding photoprotective quenching in mosses.

biophysics↗