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

Abstract

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.

Stepwise evolution of supercomplex formation with photosystem I is required for stabilization of chloroplast NADH dehydrogenase‐like complex: Lhca5‐dependent supercomplex formation in Physcomitrella patens

“…The NDH complex forms a supercomplex with PSI−LHCI depending on the Lhca5 protein in Physcomitrella (Figures 2–4; Table ). In the previous study, we showed that, in Arabidopsis, Lhca5 substitutes for Lhca4 and formed a Lhca1/Lhca5 heterodimer in the NDH–PSI supercomplex in the PSI−LHCI copy associated via Lhca5 (Otani et al ., ). However, the Lhca4 gene does not exist in the Physcomitrella genome (Alboresi et al ., ).…”

“…We could not test the stability of the other subcomplexes because of a lack of antibodies. Recently, we proposed a structural model in which SubB is the contact site with a single copy of PSIÀLHCI including Lhca6 Otani et al, 2018). On the basis of a singleparticle analysis under electron microscopy, and our structural model (Kou ril et al, 2014;Otani et al, 2018), Lhca5 should be located on the other side of the NDH complex.…”

“…In single-particle images under electron microscopy, the NDH complex is sandwiched between two copies of PSIÀLHCI in barley (Kou ril et al, 2014). In this model, the positions of linker proteins have been assigned using a combination of genetics and biochemistry: Lhca5 substitutes for Lhca4 in the right copy of PSI-LHCI, whereas Lhca6 substitutes for Lhca2 in the left copy of PSI-LHCI, when viewed from the stromal side, placing SubA at the top (Otani et al, 2018). SubB provides the binding site for Lhca6, and this binding occurs before the full assembly of the NDH complex .…”

Isolation and characterization of a large photosystem I–light‐harvesting complex II supercomplex with an additional Lhca1–a4 dimer in Arabidopsis

“…For PSI–NDH, the interaction between PSI and NDH involves other parts of the PSI complex and would involve the low abundant Lhca5 and Lhca6 isoforms located at different positions to the Lhca1–a4 dimer identified here. Specifically, the Lhca5 and Lhca6 proteins are proposed to be next to the Lhca2–a3 dimer (Kouřil et al , ), or at the place of Lhca4 and Lhca2, respectively (Otani et al , ). For the PSI–Cytb 6 f complex, EM visualization indicates that the interaction between the two complexes is next to normal Lhca1 and far away from the position of the extra Lhca1–a4 extra dimer described here, and the dimer itself was also not detected (Yadav et al , ).…”

The Chloroplast RNA Binding Protein CP31A Has a Preference for mRNAs Encoding the Subunits of the Chloroplast NAD(P)H Dehydrogenase Complex and Is Required for Their Accumulation

“…To analyze the effect of reduced ndh mRNAs on the NDH complex, we isolated thylakoid membranes from wild-type, cp31a mutants and crr2-2 control mutants and subjected them to immunoblot analysis ( Figure 3 a). There were no working antibodies available to us for the chloroplast encoded subunits of the NDH complex, but is has been shown that the nuclear-encoded subunit NdhL is affected in mutants of the chloroplast-encoded subunits NdhB, D, and F [ 23 ]. However, both NdhL as well as a second nuclear-encoded NDH subunit, PnsB2, accumulate to almost WT levels in the cp31a mutant.…”