Cryo-EM structures of photocomplexes from the free-living aerobic anoxygenic phototrophic bacterium Erythrobacter sanguineus

Xing-Yu Yue; Guang-Lei Wang; Mei-Juan Zou; Fei Ma; Zheng-Yu Wang-Otomo; Michael T Madigan; Long-Jiang Yu

doi:10.1016/j.str.2025.10.017

Cryo-EM structures of photocomplexes from the free-living aerobic anoxygenic phototrophic bacterium Erythrobacter sanguineus

Structure. 2026 Feb 5;34(2):334-348.e3. doi: 10.1016/j.str.2025.10.017. Epub 2025 Nov 21.

Authors

Xing-Yu Yue¹, Guang-Lei Wang¹, Mei-Juan Zou², Fei Ma², Zheng-Yu Wang-Otomo³, Michael T Madigan⁴, Long-Jiang Yu⁵

Affiliations

¹ Photosynthesis Research Center, State Key Laboratory of Forage Breeding-by-Design and Utilization, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² Photosynthesis Research Center, State Key Laboratory of Forage Breeding-by-Design and Utilization, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
³ Faculty of Science, Ibaraki University, Mito 310-8512, Japan.
⁴ School of Biological Sciences, Department of Microbiology, Southern Illinois University, Carbondale, IL 62901, USA.
⁵ Photosynthesis Research Center, State Key Laboratory of Forage Breeding-by-Design and Utilization, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 100049, China; China National Botanical Garden, Beijing 100093, China; Academician Workstation of Agricultural High-Tech industrial Area of the Yellow River Delta, National Center of Technology Innovation for Comprehensive Utilization of Saline-Alkali Land, Dongying 257300, China. Electronic address: longer@ibcas.ac.cn.

PMID: 41274286
DOI: 10.1016/j.str.2025.10.017

Abstract

Aerobic anoxygenic phototrophic bacteria (AAPB) are widely distributed in nature and they are important members of the marine phototrophic community. However, a structural and functional understanding of the AAPB photosynthetic apparatus is still lacking. Here, we present cryo-EM structures of the LH1-RC (core) and LH2 (peripheral) photocomplexes from the model aerobic phototroph Erythrobacter (Ery.) sanguineus. The LH1 αβ-heterodimers bind the carotenoids bacteriorubixanthinal and caloxanthin-pigments that are absent from anaerobic anoxygenic phototrophs-to form a closed ring structure. Ery. sanguineus LH1-RC contains a lipid-anchored polypeptide unrelated to any of the auxiliary proteins identified in the core complexes of purple bacteria so far. The Ery. sanguineus LH2 complex shows unique absorption characteristics, with its Q_y transition being blue-shifted to 814 nm. This work provides structural insights into the unusual photosynthetic properties of AAPB and points to new avenues to further explore their biology.

Keywords: AAPB; Erythrobacter sanguineus; LH1–RC; LH2; aerobic anoxygenic phototrophic bacteria; carotenoid; photocomplex; photosynthesis; photosynthetic bacteria.

MeSH terms

Bacterial Proteins* / chemistry
Bacterial Proteins* / metabolism
Carotenoids / chemistry
Carotenoids / metabolism
Cryoelectron Microscopy
Light-Harvesting Protein Complexes* / chemistry
Light-Harvesting Protein Complexes* / metabolism
Models, Molecular
Photosynthesis
Protein Binding
Sphingomonadaceae* / chemistry
Sphingomonadaceae* / metabolism

Substances

Light-Harvesting Protein Complexes
Bacterial Proteins
Carotenoids