Nagao Ryo, Ogawa Haruya, Suzuki Takehiro, Dohmae Naoshi, Kato Koji, Nakajima Yoshiki, Shen Jian-Ren
Faculty of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan.
Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530, Japan.
Photosynth Res. 2025 Jan 27;163(1):14. doi: 10.1007/s11120-024-01134-1.
Red algae are photosynthetic eukaryotes whose light-harvesting complexes (LHCs) associate with photosystem I (PSI). In this study, we examined characteristics of PSI-LHCI, PSI, and LHCI isolated from the red alga Galdieria sulphuraria NIES-3638. The PSI-LHCI supercomplexes were purified using anion-exchange chromatography followed by hydrophobic-interaction chromatography, and finally by trehalose density gradient centrifugation. PSI and LHCI were similarly prepared following the dissociation of PSI-LHCI with Anzergent 3-16. Polypeptide analysis of PSI-LHCI revealed the presence of PSI and LHC proteins, along with red-lineage chlorophyll a/b-binding-like protein (RedCAP), which is distinct from LHC proteins within the LHC protein superfamily. RedCAP, rather than LHC proteins, exhibited tight binding to PSI. Carotenoid analysis of LHCI identified zeaxanthin, β-cryptoxanthin, and β-carotene, with zeaxanthin particularly enriched, which is consistent with other red algal LHCIs. A Qy peak of chlorophyll a in the LHCI absorption spectrum was blue-shifted compared with those of PSI-LHCI and PSI, and a fluorescence emission peak was similarly shifted to shorter wavelengths. Based on these results, we discuss the diversity of LHC proteins and RedCAP in red algal PSI-LHCI supercomplexes.
红藻是光合真核生物，其捕光复合体（LHCs）与光系统I（PSI）相关联。在本研究中，我们研究了从红藻嗜硫加尔迪藻NIES-3638中分离出的PSI-LHCI、PSI和LHCI的特性。PSI-LHCI超复合体通过阴离子交换色谱法，随后进行疏水相互作用色谱法，最后通过海藻糖密度梯度离心法进行纯化。在用Anzergent 3-16使PSI-LHCI解离后，以类似的方式制备PSI和LHCI。对PSI-LHCI的多肽分析表明存在PSI和LHC蛋白，以及红系叶绿素a/b结合样蛋白（RedCAP），它与LHC蛋白超家族中的LHC蛋白不同。与LHC蛋白相比，RedCAP与PSI表现出紧密结合。对LHCI的类胡萝卜素分析鉴定出玉米黄质、β-隐黄质和β-胡萝卜素，其中玉米黄质特别富集，这与其他红藻LHCI一致。与PSI-LHCI和PSI相比，LHCI吸收光谱中叶绿素a的Qy峰发生蓝移，荧光发射峰也类似地移向更短波长。基于这些结果，我们讨论了红藻PSI-LHCI超复合体中LHC蛋白和RedCAP的多样性。
