7VRJ

STRUCTURE OF PHOTOSYNTHETIC LH1-RC SUPER-COMPLEX OF Allochromatium tepidum

Summary for 7VRJ

• Entry DOI: 10.2210/pdb7vrj/pdb
• EMDB information: 32100
• Descriptor: Photosynthetic reaction center cytochrome c subunit, HEME C, MAGNESIUM ION, ... (25 entities in total)
• Functional Keywords: lh1-rc complex, photosynthesis, purple bacteria
• Biological source: Allochromatium tepidum; More
• Total number of polymer chains: 36
• Total formula weight: 404878.98

Authors

Tani, K.,Kobayashi, K.,Hosogi, N.,Ji, X.-C.,Nagashima, S.,Nagashima, K.V.P.,Tsukatani, Y.,Kanno, R.,Hall, M.,Yu, L.-J.,Ishikawa, I.,Okura, Y.,Madigan, M.T.,Mizoguchi, A.,Humbel, B.M.,Kimura, Y.,Wang-Otomo, Z.-Y. (deposition date: 2021-10-23, release date: 2022-05-04, Last modification date: 2022-06-08)

Primary citation

Tani, K.,Kobayashi, K.,Hosogi, N.,Ji, X.C.,Nagashima, S.,Nagashima, K.V.P.,Izumida, A.,Inoue, K.,Tsukatani, Y.,Kanno, R.,Hall, M.,Yu, L.J.,Ishikawa, I.,Okura, Y.,Madigan, M.T.,Mizoguchi, A.,Humbel, B.M.,Kimura, Y.,Wang-Otomo, Z.Y.
A Ca 2+ -binding motif underlies the unusual properties of certain photosynthetic bacterial core light-harvesting complexes.
J.Biol.Chem., 298:101967-101967, 2022

PubMed Abstract: The mildly thermophilic purple phototrophic bacterium Allochromatium tepidum provides a unique model for investigating various intermediate phenotypes observed between those of thermophilic and mesophilic counterparts. The core light-harvesting (LH1) complex from A. tepidum exhibits an absorption maximum at 890 nm and mildly enhanced thermostability, both of which are Ca-dependent. However, it is unknown what structural determinants might contribute to these properties. Here, we present a cryo-EM structure of the reaction center-associated LH1 complex at 2.81 Å resolution, in which we identify multiple pigment-binding α- and β-polypeptides within an LH1 ring. Of the 16 α-polypeptides, we show that six (α1) bind Ca along with β1- or β3-polypeptides to form the Ca-binding sites. This structure differs from that of fully Ca-bound LH1 from Thermochromatium tepidum, enabling determination of the minimum structural requirements for Ca-binding. We also identified three amino acids (Trp44, Asp47, and Ile49) in the C-terminal region of the A. tepidum α1-polypeptide that ligate each Ca ion, forming a Ca-binding WxxDxI motif that is conserved in all Ca-bound LH1 α-polypeptides from other species with reported structures. The partial Ca-bound structure further explains the unusual phenotypic properties observed for this bacterium in terms of its Ca-requirements for thermostability, spectroscopy, and phototrophic growth, and supports the hypothesis that A. tepidum may represent a "transitional" species between mesophilic and thermophilic purple sulfur bacteria. The characteristic arrangement of multiple αβ-polypeptides also suggests a mechanism of molecular recognition in the expression and/or assembly of the LH1 complex that could be regulated through interactions with reaction center subunits.

PubMed: 35460693
DOI: 10.1016/j.jbc.2022.101967

Experimental method

ELECTRON MICROSCOPY (2.81 Å)