NADH:ubiquinone oxidoreductase from bovine heart mitochondria A fourth nuclear encoded subunit with a homologue encoded in chloroplast genomes

Abstract

The amino acid sequence has been determined of the precursor ofa nuclear encoded 20 kDa subunit ofcomplex I from bovine heart mitochondria. The sequence of the mature protein is related to a protein of uncertain function, hitherto known as psbG, encoded in jhe chloroplast genomes of higher plants. Open reading frames encoding homologues of psbCi have also been detected in bacteria aud in the mitochondrial genomc of Purarn~ci~r~ retmurekt. The chloroplast p&G gcnc is found between n&C and n&J, which encode homologues of ND3. a hydrophobic subunit of complex 1 encoded in the bovine mitochondrial genome, and of the nuclear encoded 30 k'3a subunit of complex 1. This 20 kDa protein is the eleventh out of the forty or more subunits of bovine complex I with a chloroplast encoded homologue. and its sequence provides further support for the prcsencc in chloroplasts of a multisubunit enzyme related to complex I that could be involved in chlororespiration. The strict conservation of threr: cyst&es suggests that the subunit might be an iron-sulphur protein.Complex I (bovine heart mitochondria): Chloroplast genome homologue 1, 1NTRODUCTIONNADH:ubiquinone oxidoreductase (complex I) from bovine heart mitochondria is now known to be a multisubunit assembly of at least 41 different polypeptides [ 121. Seven of them (known as NDI-ND6 and ND4L) are encoded in mitochondrial DNA [3-61, and the remainder are the products of nuclear genes that are imported into the organelle. Homologues of NDl-ND6 and of ND41 were found to be encoded in the chloroplast genomes of higher plants [7-g], and this observation led to the suggestion that chloroplasts contain an enzyme related to complex I, possibly an NAD(P)H:plastoquinone oxidoreductasc involved in a chlororespiratory pathway, although such an enzyme has yet to be purified and characterized. The finding that three nuclear encoded components of mitochondrial complex I have chloroplast encoded homologues [lo-121 provided additional support for the suggestion, and it is endorsed by the results described in the present paper. They show that a nuclear coded 20 kDa component of bovine complex I is related to another protein encoded in chloroplast genomes. This protein, known in the past as psbG, had been thought to be a component of photosystem II [ 131, but this was later shown to be incorrect [14]. It is now much more likely that psbG together with the other chloroplast encoded homologues of complex I is part of a chloroplast multisubunit complex related to complex I. The function of the mitochondrial subunit is not known. Its sequence contains three strictly conserved cysteines which might suggest that it is an iron-sulphur protein. This is consistent with the isolation of the protein from a preparation of a water-soluble fraction of bovine complex I, known as the iron-sulphur protein or IP fraction [ 1 S], and its presence in a sub-complex called Ia, which represents an extensive extramembrane domain containing the NADH binding site, FMN and all of the Fe-S clusters that have been detected by...

Nickel hydrogenases: in search of the active site

“…5). Surprisingly this pattern is also found [14] in the PSST subunit of mitochondrial NADH:O oxidoreductase [15,66], except for the first Cys which is a Leu there. In 17 Ni-hydrogenases 6 additional conservative Cys residues are found in three more motifs (motifs 4S-6S; see Fig.…”

Immunopurification of a subcomplex of the NAD(P)H‐plastoquinone‐oxidoreductase from the cyanobacterium Synechocystis sp. PCC6803

“…The 49 kDa protein is homologous to NDH-H [32] and the 30 kDa protein to NDH-J [33,34]. Recently, Masui et al [35] have suggested that two more subunits belong to this fragment: a protein of 20 kDa (in the bovine enzyme) which is homologous to NDH-K [35,36] and the B13 protein [24,35]. Thus at least three, or if the 14 kDa polypeptide (B13 homologue) is included, maybe four polypeptides, are the same in the iron-protein fragment and our preparation.…”

Studies on the expression of NDH-H, a subunit of the NAD(P)H-plastoquinone-oxidoreductase of higher-plant chloroplasts

“…Steinmiiller;FAX: 49(211) homology to mammalian mitochondrial genes, which encode subunits of the NADH-ubiquinone-oxidoreductase (complex I) of the respiratory chain (Chomyn et al 1985(Chomyn et al , 1986. Recently, it was shown that four more reading frames of plastid DNA have homology to subunits of complex I and these were therefore designated as ndh genes: ndhH (Fearnley et al 1989), ndhI (WU et al 1989;Dupuis et al 1991), ndhJ (Videira et al 1990;Pilkington et al 1991) and ndhK (Berger et al 1991;Masui et al 1991 ;Arizmendi et al 1992).…”

“…This view was questioned by the finding that the protein occurs predominantly in stroma thylakoids and it was suggested that it is an NDH subunit (Nixon et al 1989). Since a 20-kDa polypeptide with homology to NDH-K (PSII-G) has recently been identified in a complex-I preparation from bovine heart (Masui et al 1991;Arizmendi et al 1992), the classification as an NDH-protein is justified. The other subunit, the NDH-I protein (also designated as FRX-B, because of its ho-26 mology to ferredoxins), was originally found as a protein which binds to the replicative origin of chloroplast DNA (Wu et al 1989).…”