Download MendeleyA Ca 2+ -binding motif underlies the unusual properties of certain photosynthetic bacterial core light-harvesting complexes.
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.(2022) J Biol Chem 298: 101967-101967
- PubMed: 35460693
- DOI: https://doi.org/10.1016/j.jbc.2022.101967
- Primary Citation of Related Structures:
7VRJ - 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 2+ -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 2+ along with β1- or β3-polypeptides to form the Ca 2+ -binding sites. This structure differs from that of fully Ca 2+ -bound LH1 from Thermochromatium tepidum, enabling determination of the minimum structural requirements for Ca 2+ -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 2+ -binding WxxDxI motif that is conserved in all Ca 2+ -bound LH1 α-polypeptides from other species with reported structures. The partial Ca 2+ -bound structure further explains the unusual phenotypic properties observed for this bacterium in terms of its Ca 2+ -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.
Organizational Affiliation:
Graduate School of Medicine, Mie University, Tsu, Japan. Electronic address: ktani@doc.medic.mie-u.ac.jp.
