NdhM Subunit Is Required for the Stability and the Function of NAD(P)H Dehydrogenase Complexes Involved in CO2 Uptake in Synechocystis sp. Strain PCC 6803

Abstract

The cyanobacterial type I NAD(P)H dehydrogenase (NDH-1) complexes play a crucial role in a variety of bioenergetic reactions such as respiration, CO2 uptake, and cyclic electron transport around photosystem I. Two types of NDH-1 complexes, NDH-1MS and NDH-1MS′, are involved in the CO2 uptake system. However, the composition and function of the complexes still remain largely unknown. Here, we found that deletion of ndhM caused inactivation of NDH-1-dependent cyclic electron transport around photosystem I and abolishment of CO2 uptake, resulting in a lethal phenotype under air CO2 condition. The mutation of NdhM abolished the accumulation of the hydrophilic subunits of the NDH-1, such as NdhH, NdhI, NdhJ, and NdhK, in the thylakoid membrane, resulting in disassembly of NDH-1MS and NDH-1MS′ as well as NDH-1L. In contrast, the accumulation of the hydrophobic subunits was not affected in the absence of NdhM. In the cytoplasm, the NDH-1 subcomplex assembly intermediates including NdhH and NdhK were seriously affected in the ΔndhM mutant but not in the NdhI-deleted mutant ΔndhI. In vitro protein interaction analysis demonstrated that NdhM interacts with NdhK, NdhH, NdhI, and NdhJ but not with other hydrophilic subunits of the NDH-1 complex. These results suggest that NdhM localizes in the hydrophilic subcomplex of NDH-1 complexes as a core subunit and is essential for the function of NDH-1MS and NDH-1MS′ involved in CO2 uptake in Synechocystis sp. strain PCC 6803.

Functional characterization of the subunits N, H, J, and O of the NAD(P)H dehydrogenase complexes in Synechocystis sp. strain PCC 6803

“…Our previous results demonstrated that the NDH-1 assembly intermediates, including NdhH, NdhK, and NdhM, were seriously affected in the DndhM or DndhK mutant (He et al, 2016). Here, we generated a new antibody against NdhJ of Synechocystis 6803 and showed that in the wild type, NdhH, NdhJ, Figure 7.…”

“…7). Our recent studies demonstrated that the formation of 100 kD assembly intermediate was not impaired in the DndhI mutant (He et al, 2016). For some unknown reason, Peng et al (2012) could not detect NdhI in the 2D CN/SDS-PAGE in chloroplast stroma.…”

“…The Glc-tolerant strain of the wild-type Synechocystis 6803 and mutants, DndhM (He et al, 2016), DndhM/psbA2::ndhM, DndhN/DndhM/psbA2::ndhM, DndhH/DndhM/psbA2::ndhM, DndhJ/DndhM/psbA2::ndhM, and DndhO were cultured at 30°C in BG-11 medium (Allen, 1968), buffered with Tris-HCl (5 mM, pH 8.0), and bubbled with 5% (v/v) CO 2 in air. The solid medium used was BG-11 supplemented with 1.5% agar.…”

“…Further electron microscopy investigations speculated that in Synechocystis 6803, the NdhL-NdhO subunits are located together, constituting the oxygenic photosynthesis specific (OPS) domain (Birungi et al, 2010). However, our previous study demonstrates that cyanobacterial NdhM is localized in the hydrophilic subcomplex of NDH-1 complexes and is essential for the function of NDH-1 complexes (He et al, 2016). Nowaczyk et al (2011) reported two novel small subunits, NdhP and NdhQ, which were included in the purified NDH-1L complex by Ni 2+ affinity chromatography and sizeexclusion chromatography from T. elongatus.…”

“…4A). For construction of the ndhN, ndhH, and ndhJ null mutants, we used the DndhM mutant strain in which the ndhM gene had been deleted and the hydrophilic subunits of NDH-1 complex could not be accumulated in the thylakoid membrane (He et al, 2016). The ndhN, ndhH, and ndhJ genes were inactivated in the DndhM background.…”