1. Structural insights into blue-green light utilization by marine green algal light harvesting complex II at 2.78 Å
- Author
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Soichiro Seki, Tetsuko Nakaniwa, Pablo Castro-Hartmann, Kasim Sader, Akihiro Kawamoto, Hideaki Tanaka, Pu Qian, Genji Kurisu, and Ritsuko Fujii
- Subjects
Intermonomer chlorophyll b macrocluster ,Codium fragile ,Biophysics ,Light-harvesting complex ,Siphonaxanthin–chlorophyll a/b-binding protein (SCP) ,Biochemistry ,Research Article ,Cryo-EM - Abstract
研究グループは、高分解能の電子顕微鏡を用いた解析により、海洋性緑藻ミルの光合成アンテナと呼ばれるタンパク質内での色素の構造と結合環境を初めて明らかにしました。その結果、海水中で得られる唯一の光である青緑色光を効率よく光合成に利用する分子メカニズムがより鮮明になりました。, Light-harvesting complex II (LHCII) present in plants and green algae absorbs solar energy to promote photochemical reactions. A marine green macroalga, Codium fragile, exhibits the unique characteristic of absorbing blue-green light from the sun during photochemical reactions while being underwater owing to the presence of pigment-altered LHCII called siphonaxanthin–chlorophyll a/b-binding protein (SCP). In this study, we determined the structure of SCP at a resolution of 2.78 Å using cryogenic electron microscopy. SCP has a trimeric structure, wherein each monomer containing two lutein and two chlorophyll a molecules in the plant-type LHCII are replaced by siphonaxanthin and its ester and two chlorophyll b molecules, respectively. Siphonaxanthin occupies the binding site in SCP having a polarity in the trimeric inner core, and exhibits a distorted conjugated chain comprising a carbonyl group hydrogen bonded to a cysteine residue of apoprotein. These features suggest that the siphonaxanthin molecule is responsible for the characteristic green absorption of SCP. The replaced chlorophyll b molecules extend the region of the stromal side chlorophyll b cluster, spanning two adjacent monomers.
- Published
- 2022