The Gene sml0013 of Synechocystis Species Strain PCC 6803 Encodes for a Novel Subunit of the NAD(P)H Oxidoreductase or Complex I That Is Ubiquitously Distributed among Cyanobacteria  

Abstract

The NAD(P)H oxidoreductase or complex I (NDH1) complex participates in many processes such as respiration, cyclic electron flow, and inorganic carbon concentration in the cyanobacterial cell. Despite immense progress in our understanding of the structure-function relation of the cyanobacterial NDH1 complex, the subunits catalyzing NAD(P)H docking and oxidation are still missing. The gene sml0013 of Synechocystis 6803 encodes for a small protein of unknown function for which homologs exist in all completely known cyanobacterial genomes. The protein exhibits weak similarities to the NDH-dependent flow6 (NDF6) protein, which was reported from Arabidopsis (Arabidopsis thaliana) chloroplasts as a NDH subunit. An sml0013 inactivation mutant of Synechocystis 6803 was generated and characterized. It showed only weak differences regarding growth and pigmentation in various culture conditions; most remarkably, it exhibited a glucose-sensitive phenotype in the light. The genome-wide expression pattern of the Dsml0013::Km mutant was almost identical to the wild type when grown under high CO 2 conditions as well as after shifts to low CO 2 conditions. However, measurements of the photosystem I redox kinetic in cells of the Dsml0013::Km mutant revealed differences, such as a decreased capability of cyclic electron flow as well as electron flow into respiration in comparison with the wild type. These results suggest that the Sml0013 protein (named NdhP) represents a novel subunit of the cyanobacterial NDH1 complex, mediating its coupling either to the respiratory or the photosynthetic electron flow.

NdhP Is an Exclusive Subunit of Large Complex of NADPH Dehydrogenase Essential to Stabilize the Complex in Synechocystis sp. Strain PCC 6803

“…The transposon insertion occurred at position 3188117 of the Synechocystis 6803 genome (49). This implies that inactivation of ndhP impairs NDH-CET activity, as suggested recently by Schwarz et al (24).…”

“…The NDH-1L complex is involved in respiration and NDH-CET (3), which explains the impairment of these activities in the ⌬ndhP mutant of Synechocystis 6803 (Figs. 1B and 2, D-F) (24).…”

“…Identification of NdhP-YFP-His 6 in various ndh mutants at DNA (D) and protein (E) levels. D, PCR segregation analysis of NdhP-YFP-His 6 in WT, ⌬ndhS, ⌬ndhD1/D2 (⌬D1/D2), and M55 having NdhP-YFP-His 6 using the ndhP-yfp-his6-E and -F primer sequences (supplemental Table 1 Synechocystis 6803 (24). However, how NdhP affected the respiratory and cyclic electron flows is poorly understood.…”

“…Deletion of ndhP in Synechocystis 6803 led to the cells unable to grow under photoheterotrophic conditions (24). It was suggested that NdhP is involved in the respiratory and cyclic electron flows, but the role of this subunit is not known.…”

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

“…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. Recently, it has been demonstrated that NdhP and NdhQ are involved in respiration and CET and are required to stabilize the NDH-1L complex (Schwarz et al, 2013;Wulfhorst et al, 2014;Zhang et al, 2014;Zhao et al, 2015). In recent years, it has been reported that the newly identified OPS subunit, NdhS from Arabidopsis (also known as CRR31) or from Synechocystis 6803 contains Src homology 3 domain-like fold, which serves as the ferredoxin (Fd) docking site domain (Yamamoto et al, 2011;Battchikova et al, 2011b;Yamamoto and Shikanai, 2013), and the authors suggested that the chloroplast NDH complex could accept electrons from Fd rather than NAD(P)H. By studying the purified NDH-1L complex from the thermophilic cyanobacterium T. elongatus, we demonstrated that NDH-1L Figure 1.…”