The reaction center-light harvesting 1 (RC-LH1) complex converts solar energy into electrical energy, driving the initiation of photosynthesis. The authors present a cryo-electron microscopy structure of the RC-LH1 isolated from a marine photoheterotrophic bacterium Dinoroseobacter shibae. The RC comprises four subunits, including a three-heme cytochrome (Cyt) c protein, and is surrounded by a closed LH ring composed of 17 pairs of antenna subunits. Notably, a novel subunit with an N-terminal "helix-turn-helix" motif embedded in the gap between the RC and the LH ring is identified. The purified RC-LH1 complex exhibits high stability in solutions containing Mg2+ or Ca2+. The periplasmic Cyt c2 is predicted to bind at the junction between the Cyt subunit and the membrane plane, enabling electron transfer from Cyt c2 to the proximal heme of the tri-heme Cyt, and subsequently to the special pair of bacteriochlorophylls. These findings provide structural insights into the efficient energy and electron transfer processes within a distinct type of RC-LH1, and shed light on evolutionary adaptations of photosynthesis.

Center of Cryo Electron Microscopy Zhejiang University School of Medicine Hangzhou Zhejiang 310058 China

College of Life Sciences Zhejiang University Hangzhou Zhejiang 310058 China

Department of Microbiology and Immunology University of British Columbia Vancouver BC V6T 1Z3 Canada

Department of Pathology of Sir Run Run Shaw Hospital Department of Biophysics Zhejiang University School of Medicine Hangzhou Zhejiang 310058 China

Laboratory of Anoxygenic Phototrophs Institute of Microbiology Czech Academy of Science Třeboň 37981 Czechia

Photosynthesis Research Center Key Laboratory of Photobiology Institute of Botany Chinese Academy of Sciences Beijing 100093 China

Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology Okayama University Okayama 700 8530 Japan

State Key Laboratory of Marine Environmental Science College of Ocean and Earth Sciences Xiamen University Xiamen Fujian 361005 China

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