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Specific substitutions of light‐harvesting complex I proteins associated with photosystem I are required for supercomplex formation with chloroplast NADH dehydrogenase‐like complex
Author(s) -
Otani Takuto,
Kato Yoshinobu,
Shikanai Toshiharu
Publication year - 2018
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13846
Subject(s) - photosystem i , chloroplast , protein subunit , mutant , thylakoid , biology , photosystem ii , photosynthesis , chemistry , photosystem , crystallography , biophysics , biochemistry , gene
Summary In Arabidopsis, the chloroplast NADH ‐dehydrogenase‐like ( NDH ) complex is sandwiched between two copies of photosystem I ( PSI ) supercomplex, consisting of a PSI core and four light‐harvesting complex I ( LHCI ) proteins ( PSI ‐ LHCI ) to form the NDH – PSI supercomplex. Two minor LHCI proteins, Lhca5 and Lhca6, contribute to the interaction of each PSI – LHCI copy with the NDH complex. Here, large‐pore blue‐native gel electrophoresis revealed that, in addition to this complex, there were at least two types of higher‐order association of more LHCI copies with the NDH complex. In single‐particle images, this higher‐order association of PSI – LHCI preferentially occurs at the left side of the NDH complex when viewed from the stromal side, placing subcomplex A at the top (Yadav et al ., Biochim. Biophys. Acta ‐ Bioenerg ., 1858, 2017, 12). The association was impaired in the lhca6 mutant but not in the lhca5 mutant, suggesting that the left copy of PSI – LHCI was linked to the NDH complex via Lhca6. From an analysis of subunit compositions of the NDH – PSI supercomplex in lhca5 and lhca6 mutants, we propose that Lhca6 substitutes for Lhca2 in the left copy of PSI – LHCI , whereas Lhca5 substitutes for Lhca4 in the right copy. In the lhca2 mutant, Lhca3 was specifically stabilized in the NDH – PSI supercomplex through heterodimer formation with Lhca6. In the left copy of PSI – LHCI , subcomplex B, Lhca6 and NdhD likely formed the core of the supercomplex interaction. In contrast, a larger protein complex, including at least subcomplexes B and L and NdhB, was needed to form the contact site with Lhca5 in the right copy of PSI – LHCI .