3 years ago

Specific substitutions of light-harvesting complex I proteins associated with photosystem I are required for supercomplex formation with chloroplast NADH dehydrogenase-like complex

Yoshinobu Kato, Takuto Otani, Toshiharu Shikanai
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., 2017). 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 though 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. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/tpj.13846

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