C-terminal cleavage of the LH1 α-polypeptide in the Sr2+-cultured Thermochromatium tepidum

Yukihiro Kimura, Tomoaki Kawakami, Teruhisa Arikawa, Yong Li, Long-Jiang Yu, Takashi Ohno, Michael T. Madigan, Zheng Yu Wang-Otomo

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1 Citation (Scopus)

Abstract

The light-harvesting 1 reaction center (LH1-RC) complex in the thermophilic purple sulfur bacterium Thermochromatium (Tch.) tepidum binds Ca ions as cofactors, and Ca-binding is largely involved in its characteristic Qy absorption at 915 nm and enhanced thermostability. Ca2+ can be biosynthetically replaced by Sr2+ in growing cultures of Tch. tepidum. However, the resulting Sr2+-substituted LH1-RC complexes in such cells do not display the absorption maximum and thermostability of those from Ca2+-grown cells, signaling that inherent structural differences exist in the LH1 complexes between the Ca2+- and Sr2+-cultured cells. In this study, we examined the effects of the biosynthetic Sr2+-substitution and limited proteolysis on the spectral properties and thermostability of the Tch. tepidum LH1-RC complex. Preferential truncation of two consecutive, positively charged Lys residues at the C-terminus of the LH1 α-polypeptide was observed for the Sr2+-cultured cells. A proportion of the truncated LH1 α-polypeptide increased during repeated subculturing in the Sr2+-substituted medium. This result suggests that the truncation is a biochemical adaptation to reduce the electrostatic interactions and/or steric repulsion at the C-terminus when Sr2+ substitutes for Ca2+ in the LH1 complex. Limited proteolysis of the native Ca2+-LH1 complex with lysyl protease revealed selective truncations at the Lys residues in both C- and N-terminal extensions of the α- and β-polypeptides. The spectral properties and thermostability of the partially digested native LH1-RC complexes were similar to those of the biosynthetically Sr2+-substituted LH1-RC complexes in their Ca2+-bound forms. Based on these findings, we propose that the C-terminal domain of the LH1 α-polypeptide plays important roles in retaining proper structure and function of the LH1-RC complex in Tch. tepidum.

Original languageEnglish
Pages (from-to)1-9
Number of pages9
JournalPhotosynthesis Research
DOIs
Publication statusAccepted/In press - May 10 2017
Externally publishedYes

Keywords

  • C-terminal truncation
  • Calcium
  • Light-harvesting 1 reaction center
  • Strontium
  • Thermochromatium tepidum
  • Thermophilic purple bacteria

ASJC Scopus subject areas

  • Biochemistry
  • Plant Science
  • Cell Biology

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    Kimura, Y., Kawakami, T., Arikawa, T., Li, Y., Yu, L-J., Ohno, T., Madigan, M. T., & Wang-Otomo, Z. Y. (Accepted/In press). C-terminal cleavage of the LH1 α-polypeptide in the Sr2+-cultured Thermochromatium tepidum. Photosynthesis Research, 1-9. https://doi.org/10.1007/s11120-017-0393-8