This family is found in Bacteria and Streptophyta includes members such as NdhS (NAD(P)H-quinone oxidoreductase subunit S). NdhS, also known as CRR31 (chlororespiratory reduction 31), is a subunit of the chloroplast NADH dehydrogenase-like (NDH) complex [1]. It is also a subunit of the cyanobacterial NDH-1 complex [2] [3]. NAD(P)H-oxidizing subunits have not been found in chloroplasts or cyanobacteria, where ferredoxin is probably the electron donor. NdhS contributes to the formation of a ferredoxin binding site of NDH [1] and is necessary for high affinity binding of ferredoxin [4]. The cyanobacterial NDH-1 complex, also known as NADPH:plastoquinone oxidoreductase or type I NAD(P)H dehydrogenase, is involved in plastoquinone reduction and cyclic electron transfer (CET) around photosystem I. The chloroplast NDH is more similar to cyanobacterial NDH-1, which is believed to be the origin of chloroplast NDH, than to mitochondrial NADH dehydrogenase present in the same species [5] [6]. The NDH complexes of chloroplasts, however, contain many subunits that are absent from cyanobacterial NDH-1 complexes.

1: An Src homology 3 domain-like fold protein forms a ferredoxin binding site for the chloroplast NADH dehydrogenase-like complex in Arabidopsis. Yamamoto H, Peng L, Fukao Y, Shikanai T; Plant Cell. 2011;23:1480-1493. PMID:21505067

2: Identification of novel Ssl0352 protein (NdhS), essential for efficient operation of cyclic electron transport around photosystem I, in NADPH:plastoquinone oxidoreductase (NDH-1) complexes of Synechocystis sp. PCC 6803. Battchikova N, Wei L, Du L, Bersanini L, Aro EM, Ma W; J Biol Chem. 2011;286:36992-37001. PMID:21880717

3: NDH-1L interacts with ferredoxin via the subunit NdhS in Thermosynechococcus elongatus. He Z, Zheng F, Wu Y, Li Q, Lv J, Fu P, Mi H; Photosynth Res. 2015;126:341-349. PMID:25630976

4: In planta mutagenesis of Src homology 3 domain-like fold of NdhS, a ferredoxin-binding subunit of the chloroplast NADH dehydrogenase-like complex in Arabidopsis: a conserved Arg-193 plays a critical role in ferredoxin binding. Yamamoto H, Shikanai T; J Biol Chem. 2013;288:36328-36337. PMID:24225949

5: Structure of the chloroplast NADH dehydrogenase-like complex: nomenclature for nuclear-encoded subunits. Ifuku K, Endo T, Shikanai T, Aro EM; Plant Cell Physiol. 2011;52:1560-1568. PMID:21785130

6: Cyanobacterial NDH-1 complexes: novel insights and remaining puzzles. Battchikova N, Eisenhut M, Aro EM; Biochim Biophys Acta. 2011;1807:935-944. PMID:21035426