Journal of Energy Bioscience 2024, Vol.15, No.4, 255-266 http://bioscipublisher.com/index.php/jeb 260 5.2 Modifying light-harvesting complexes to increase light absorption Light-harvesting complexes (LHCs) are integral to capturing light energy and funneling it to the reaction centers of photosystems. Modifying these complexes can significantly enhance light absorption. For example, the structural and spectroscopic analysis of photosystem complexes from oxygenic photosynthetic organisms has shown that the arrangement of pigments and their connectivity are crucial for efficient energy transfer (Croce and Amerongen, 2020). Furthermore, the isolation and characterization of a large Photosystem I-Light Harvesting Complex II (PSI-LHCII) supercomplex in Arabidopsis revealed the presence of an additional Lhca1-a4 dimer, which enhances the light absorption capacity of PSI (Crepin et al., 2019) (Figure 2). These findings underscore the potential of structural modifications in LHCs to boost light absorption and improve photosynthetic performance. Figure 2 Single-particle electron microscopy (EM) analysis (Adopted from Crepin et al., 2019) Image caption: (a) Negative-staining single-particle EM analysis of the eluted PSI-LHCII fraction revealed that the main component was a well-characterized particle consisting of PSI and a single LHCII trimer (Kouřil et al., 2005; Galka et al., 2012). (b) The atomic model of PSI-LHCII (5ZJI) (Pan et al., 2018) is superimposed on the EM density map, illustrating the positions of LHCII and the Lhca1-4 subunits (view from the stromal side). (c) EM analysis of the PSI-6LHCI-LHCII fraction identified a previously undescribed particle with a large extra density on the PsaB-PsaI-PsaH side. (d) The atomic model of PSI-LHCII is superimposed to emphasize the location of the extra density in the PSI-6LHCI-LHCII complex. (e) Biochemical data suggest that the extra density corresponds to an Lhca1-4 dimer (in red), indicating an interaction between this extra dimer, the PSI core, and the LHCII trimer. (f) The atomic model of the PSI of Chlamydomonas reinhardtii (6JO5) (Suga et al., 2019) is superimposed, maintaining the same positions for the core and internal Lhca as in plant PSI, to display the position of the additional algal Lhca dimer (Lhca2-9, in yellow). In algae, this extra dimer is positioned differently compared to the extra density in the Arabidopsis PSI-6LHCI-LHCII complex. Note that the outer row of algal Lhca proteins is absent in plant PSI. See Figure S3 for further details on EM analysis (Adapted from Crepin et al., 2019)
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