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<p><i>Halorhodospira</i> (<i>Hlr</i>.) <i>halophila</i> strain BN9622 is an extremely halophilic and alkaliphilic phototrophic purple sulfur bacterium isolated from a hypersaline lake in the Libyan Desert whose total salinity exceeded 35% at pH 10.7. Here we present a cryo-EM structure of the native LH1–LH2 co-complex from strain BN9622 at 2.22 Å resolution. Surprisingly, the LH1–LH2 co-complex consists of a double-ring cylindrical structure with the larger LH1 ring encircling a smaller LH2 ring. The <i>Hlr. halophila</i> LH1 contains 18 αβ-subunits and additional bacteriochlorophyll <i>a</i> (BChl <i>a</i>) molecules that absorb maximally at 797 nm. The LH2 ring is composed of 9 αβ-subunits, and the BChl <i>a</i> molecules in the co-complex form extensive intra- and inter-complex networks to allow near 100% efficiency of energy transfer to its surrounding LH1. The additional LH1-B797 BChls <i>a</i> are located in such a manner that they facilitate exciton transfer from monomeric BChls in LH2 to the dimeric BChls in LH1. The structural features of the strain BN9622 LH1–LH2 co-complex may have evolved to allow a minimal LH2 complex to maximize excitation transfer to the core complex and effectively harvest light in the physiologically demanding ecological niche of this purple bacterium.</p>

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A distinct double-ring LH1–LH2 photocomplex from an extremophilic phototroph

  • 期刊论文

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  • 发表日期：

    2025年2月6日

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  • Kazutoshi Tani,
  • Kenji V. P. Nagashima,
  • Risa Kojima,
  • Masaharu Kondo,
  • Ryo Kanno,
  • Issei Satoh,
  • Mai Kawakami,
  • Naho Hiwatashi,
  • Kazuna Nakata,
  • Sakiko Nagashima,
  • Kazuhito Inoue,
  • Yugo Isawa,
  • Ryoga Morishita,
  • Shinichi Takaichi,
  • Endang R. Purba,
  • Malgorzata Hall,
  • Long-Jiang Yu,
  • Michael T. Madigan,
  • Akira Mizoguchi,
  • Bruno M. Humbel,
  • Yukihiro Kimura,
  • Yutaka Nagasawa,
  • Takehisa Dewa,
  • Zheng-Yu Wang-Otomo

摘要

Halorhodospira (Hlr.) halophila strain BN9622 is an extremely halophilic and alkaliphilic phototrophic purple sulfur bacterium isolated from a hypersaline lake in the Libyan Desert whose total salinity exceeded 35% at pH 10.7. Here we present a cryo-EM structure of the native LH1–LH2 co-complex from strain BN9622 at 2.22 Å resolution. Surprisingly, the LH1–LH2 co-complex consists of a double-ring cylindrical structure with the larger LH1 ring encircling a smaller LH2 ring. The Hlr. halophila LH1 contains 18 αβ-subunits and additional bacteriochlorophyll a (BChl a) molecules that absorb maximally at 797 nm. The LH2 ring is composed of 9 αβ-subunits, and the BChl a molecules in the co-complex form extensive intra- and inter-complex networks to allow near 100% efficiency of energy transfer to its surrounding LH1. The additional LH1-B797 BChls a are located in such a manner that they facilitate exciton transfer from monomeric BChls in LH2 to the dimeric BChls in LH1. The structural features of the strain BN9622 LH1–LH2 co-complex may have evolved to allow a minimal LH2 complex to maximize excitation transfer to the core complex and effectively harvest light in the physiologically demanding ecological niche of this purple bacterium.