The nuclear‐encoded polypeptide Cfo‐II from spinach is a real, ninth subunit of chloroplast ATP synthase

Abstract

Proton-translocating F-ATP synthases from chloroplasts contain a nuclear-coded subunit, CFo-II, that lacks an equivalent in the corresponding E. coil complex. Three recombinant phages that code for the entire precursor of this subunit have been isolated from 2 gtl 1 cDNA expression libraries made from polyadenylated spinach RNA using a two-step strategy. The reading frame of 222 amino acid residues includes 147 residues for the mature protein (M r 16.5 kDa) and a transit sequence of 75 residues (M r 8.0 kDa). Secondary structure predictions indicate a bitopic protein, anchored by a single N-terminal transmembrane segment and a C-terminal hydrophilic region that probably reaches into CF~. CFo-II precursor made in vitro can be imported into isolated, intact chloroplasts and assembled into ATP synthase. This protein is a real subunit of the plastid enzyme and a distinctive characteristic of ATP synthases involved in photosynthetic processes. Unique features are (i) that the gene for CFo-II (atpG) appears to be a duplication of atpF encoding CFo-I, the homologues of the genes for subunits b" and b in photosynthetic bacteria, (ii) that it represents the first instance that one copy of the various duplicated loci found in plastid chromosomes has been phylogenetically translocated to the nucleus, and (iii) that it operates with a bipartite (import/thylakoid-targeting) transit peptide but without an intermediate cleavage site for the stroma protease, suggestive of a way of membrane integration different from that of its plastome-encoded counterpart CFo-I. With these data, the first complete sequence for a chloroplast ATP synthase of a higher plant (spinach) is available.

Biochemical and electron microscopic characterization of the F1F0 ATP Synthase from the hyperthermophilic eubacterium Aquifex aeolicus

“…In contrast the F 1 F 0 ATP synthase from photosynthetic prokaryotes contains two different b subunits [50][51][52]. Now it is evident that even ancient non-photosynthetic eubacteria can possess two different b subunits.…”

Sec-independent Insertion of Thylakoid Membrane Proteins

“…However, a very different mechanism has been demonstrated for three other thylakoid proteins: subunit II of the integral CF o component of the thylakoidal ATP synthase (CF o II) and subunits X and W of photosystem II (PSII-X and PSII-W). These proteins are synthesized with bipartite presequences that strongly resemble typical Sec-type signal peptides (22)(23)(24), yet they integrate into thylakoid membranes in the absence of stromal factors, nucle-* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C.…”

ATPG is required for the accumulation and function of chloroplast ATP synthase in Arabidopsis

“…The TargerP [30] and Predotar [31] programs predicted that ATPG protein is targeted to chloroplast. Sequence alignment showed that the ATPG homologs existed in various plants, including Spinacia [15], Vitis vinifera, Oryza sativa, Populus trichocarpa, Sorghum bicolor and Physcomitrella patens. In addition, the homologs were also found in Volvox carteri, Chlamydomonas reinhardtii and Cyanophora paradoxa (Figure 1(a)).…”

“…Although the construction and function of subunit b in E. coli have been studied in great detail [13,14], the knowledge about subunits II and I of chloroplast ATP synthase is limited. The nuclear atpG gene encoding the subunit II of chloroplast ATP synthase has been thought to be a duplication of atpF encoding the subunit I [15], but the secondary structures of two subunits are different significantly. In Spinach, the subunit II is shorter than subunit I and it has been predicted to contain less -helix [12].…”