The chloroplast beta-subunit allows assembly of the Escherichia coli F0 portion of the energy transducing adenosine triphosphatase

The formation or the reduction of a disulfide bridge on the gamma subunit of chloroplast ATP synthase affects the inhibitory effect of the epsilon subunit

We have studied the change of the catalytic activity of chimeric complexes that were formed by chloroplast coupling factor 1 (CF1) -gamma, alpha and beta subunits of thermophilic bacterial F1 after formation or reduction of the disulfide bridge of different gamma subunits modified by oligonucleotide-directed mutagenesis techniques. For this purpose, three mutant gamma subunits were produced: gamma Delta194-230, here 37 amino acids from Pro-194 to Ile-230 are deleted, gammaC199A, Cys-199 is changed to Ala, and gamma Delta200-204, amino acids from Asp-200 to Lys-204 are deleted. All of the chimeric subunit complexes produced from each of these mutant CF1-gamma subunits and alpha and beta subunits from thermophilic bacterial F1 lost the sensitivity against thiol reagents when compared with the complex containing wild-type CF1-gamma. The pH optimum (pH 8.5-9.0) and the concentration of methanol to stimulate ATPase activities were not affected by these mutations. These indicate that the introduction of the mutations did not change the main features of ATPase activity of the chimeric complex. However, the interaction between gamma subunit and epsilon subunit was strongly influenced by the type of gamma subunit itself. Although the ATPase activity of the chimeric complex that contained gamma Delta200-204 or gammaC199A was inhibited by the addition of recombinant epsilon subunit from CF1 similarly to complexes containing the reduced wild-type gamma subunit, the recombinant epsilon subunit did not inhibit the ATPase of the complex, which contained the oxidized form of gamma subunit. Therefore the affinity of the epsilon subunit to the gamma subunit may be dependent on the state of the gamma subunit or the epsilon subunit may bind to the oxidized form of gamma subunit in a mode that does not inhibit the activity. The ATPase activity of the complex that contains gamma Delta194-230 was not efficiently inhibited by epsilon subunit. These results show that the formation or reduction of the disulfide bond on the gamma subunit may induce a conformational change in the region that directly affects the interaction of this subunit with the adjacent epsilon subunit.

The regulatory functions of the gamma and epsilon subunits from chloroplast CF1 are transferred to the core complex, alpha3beta3, from thermophilic bacterial F1

The expression plasmids for the subunit gamma (gamma(c)) and the subunit epsilon (epsilon(c)) of chloroplast coupling factor (CF1) from spinach were constructed, and the desired proteins were expressed in Escherichia coli. Both expressed subunits were obtained as inclusion bodies. When recombinant gamma(c) was mixed with recombinant alpha and beta subunits of F1 from thermophilic Bacillus PS3 (TF1), a chimeric subunit complex (alpha3beta3gamma(c)) was reconstituted and it showed significant ATP hydrolysis activity. The ATP hydrolysis activity of this complex was enhanced in the presence of dithiothreitol and suppressed by the addition of CuCl2, which induces formation of a disulfide bond between two cysteine residues in gamma(c). Hence, this complex has similar modulation characteristics as CF1. The effects of recombinant epsilon(c) and epsilon subunit from TF1 (epsilon(t)) on alpha3beta3gamma(c) were also investigated. Epsilon(c) strongly inhibited the ATP hydrolysis activity of chimeric alpha3beta3gamma(c) complex but epsilon(t) did not. The inhibition was abolished and the ATP hydrolysis activity was recovered when methanol was added to the assay medium. The addition of epsilon(c) or epsilon(t) to the alpha3beta3gamma(t) complex, which is the authentic subunit complex from TF1, resulted in weak stimulation of the ATP hydrolysis activity. These results suggest that (a) the specific regulatory function of gamma(c) can be transferred to the bacterial subunit complex; (b) the interaction between the gamma(c) subunit and epsilon(c) strongly affects the enzyme activity, which was catalyzed at the catalytic sites that reside on the alpha3beta3 core.

A subunit interaction in chloroplast ATP synthase determined by genetic complementation between chloroplast and bacterial ATP synthase genes

F1F0-ATP synthases utilize protein conformational changes induced by a transmembrane proton gradient to synthesize ATP. The allosteric cooperativity of these multisubunit enzymes presumably requires numerous protein-protein interactions within the enzyme complex. To correlate known in vitro changes in subunit structure with in vivo allosteric interactions, we introduced the beta subunit of spinach chloroplast coupling factor 1 ATP into a bacterial F1 ATP synthase. A cloned atpB gene, encoding the complete chloroplast beta subunit, complemented a chromosomal deletion of the cognate uncD gene in Escherichia coli and was incorporated into a functional hybrid F1 ATP synthase. The cysteine residue at position 63 in chloroplast beta is known to be located at the interface between alpha and beta subunits and to be conformationally coupled, in vitro, to the nucleotide binding site > 40 A away. Enlarging the side chain of chloroplast coupling factor 1 beta residue 63 from Cys to Trp blocked ATP synthesis in vivo without significantly impairing ATPase activity or ADP binding in vitro. The in vivo coupling of nucleotide binding at catalytic sites to transmembrane proton movement may thus involve an interaction, via conformational changes, between the amino-terminal domains of the alpha and beta subunits.

Hybrid Fo complexes of the ATP synthases of spinach chloroplasts and Escherichia coli. Immunoprecipitation and mutant analyses

Hybrid Fo complexes of the ATP synthases of spinach chloroplast (CFo) and Escherichia coli (EFo) were investigated. Immunoprecipitations with polyclonal antibodies against the different Fo subunits clearly revealed that hybrid Fo complexes derived from CFo subunit III and EFo subunits a and b were formed in vivo. In addition, the ATPase activities of the hybrid ATP synthase, measured in everted cytoplasmic membranes of an atpE mutant strain transformed with the atpH gene coding for CFo III, were comparable to activities obtained for the same mutant strain complemented with the atpE gene (EFo c). Nevertheless, CFo III was not able to replace EFo c functionally, since the strain containing the hybrid ATP synthase was not able to grow on succinate. In order to investigate the reason for this lack of function, hybrid proteolipids of CFo III and EFo c were constructed. Only a chimaeric protein comprising the seven N-terminal amino acid residues from CFo III and the remaining part of EFo c was able to replace wild-type EFo c, whereas hybrid proteins with 13 and 33 N-terminal amino acids of CFo III were not functional. The results suggested that a network of interactions between the subunits essential for proton translocation and/or coupling of the F1 part exists, which was optimized for each species during evolution, although the overall structure of FoF1 complexes has been conserved.

Over-production, renaturation and reconstitution of delta and epsilon subunits from chloroplast and cyanobacterial F1

We studied the functioning of chimeric F0F1-ATPases by replacing subunits delta and epsilon of spinach CF1 with their counterparts from Synechocystis sp. PCC 6803. The sequence identities between these subunits are 26 and 41%, respectively. For a systematic approach to such studies and later extension to genetically modified subunits recombinant proteins are required. The genes coding for spinach and Synechocystis delta and epsilon were cloned into pET3 expression vectors and expressed in Escherichia coli. Upon expression at 37 degrees C the recombinant subunits formed inclusion bodies within the host cells except for spinach delta, which was soluble. Synechocystis delta and epsilon could be obtained in soluble form upon expression at 20 degrees C. After purification (and refolding of spinach epsilon) both epsilon subunits inhibited the Ca(2+)-ATPase activity of soluble CF1(- epsilon). Subunits delta and epsilon from both species raised the rate of ATP synthesis in partially CF1-depleted spinach thylakoids when added together with CF1(- delta) or CF1(- delta, epsilon). This showed the functionality of recombinant Synechocystis and spinach delta and epsilon together with spinach alpha 3 beta 3 gamma. The molar excess of epsilon necessary for saturation was higher for Ca(2+)-ATPase inhibition than for reconstitution of photophosphorylation thus pointing to a direct interaction between epsilon and both CF1 and CF0.

Complementation of Escherichia coli uncD mutant strains by a chimeric F1-beta subunit constructed from E. coli and spinach chloroplast F1-beta

ATP-synthesizing F0F1-ATPases are complex enzymes consisting of at least eight different subunits. These subunits are conserved during evolution to a very variable degree ranging in pairwise comparison between, for example, Escherichia coli and spinach chloroplast from 20% to 66% identical residues. It was surprising to find that some of the less well conserved subunits like delta and epsilon could replace their E. coli counterparts, whereas the highly conserved beta subunit, which carries the active site, in the E. coli enzyme could not be substituted by spinach chloroplast beta (Lill et al. (1993) Biochim. Biophys. Acta 1144, 278-284). We constructed a chimeric F1-beta subunit consisting of spinach beta in which the 96 N-terminal amino acids were replaced by the respective residue sequence from E. coli beta. Whereas spinach beta did not complement E. coli uncD mutant strains, the chimeric beta subunit restored growth under conditions of oxidative phosphorylation.

Complementation of Escherichia coli unc mutant strains by chloroplast and cyanobacterial F1-ATPase subunits

The genes encoding the five subunits of the F1 portion of the ATPases from both spinach chloroplasts and the cyanobacterium Synechocystis sp. PCC 6803 were cloned into expression vectors and expressed in Escherichia coli. The recombinant subunits formed inclusion bodies within the cells. Each particular subunit was expressed in the respective unc mutant, each unable to grow on non-fermentable carbon sources. The following subunits restored growth under conditions of oxidative phosphorylation: alpha (both sources, cyanobacterial subunit more than spinach subunit), beta (cyanobacterial subunit only), delta (both spinach and Synechocystis), and epsilon (both sources), whereas no growth was achieved with the gamma subunits from both sources. Despite a high degree of sequence homology the large subunits alpha and beta of spinach and cyanobacterial F1 were not as effective in the substitution of their E. coli counterparts. On the other hand, the two smallest subunits of the E. coli ATPase could be more effectively replaced by their cyanobacterial or chloroplast counterparts, although the sequence identity or even similarity is very low. We attribute these findings to the different roles of these subunits in F1: The large alpha and beta subunits contribute to the catalytic centers of the enzyme, a function rendering them very sensitive to even minor changes. For the smaller delta and epsilon subunits it was sufficient to maintain a certain tertiary structure during evolution, with little emphasis on the conservation of particular amino acids.

Added subunit beta of CF1 as well as gamma/delta/epsilon restore photophosphorylation in partially CF1-depleted thylakoids

We investigated the ability of subunits beta, gamma, delta, and epsilon of CF1, the F1-ATPase of chloroplasts, to interact with exposed CF0 in EDTA-treated, partially CF1-depleted thylakoid membranes. We measured the ability of subunits beta, gamma, delta, and epsilon to stimulate the rate of photophosphorylation under continuous light and, for subunit beta, also the ability to diminish the proton leakage through exposed CF0 by deceleration of the decay of electrochromic absorption transients under flashing light. The greatest effect was caused by subunit beta, followed by gamma/delta/epsilon. Pairwise combinations of gamma, delta, and epsilon or each of these subunits alone were only marginally effective. Subunit gamma from the thermophilic bacterium PS 3 in combination with chloroplast delta and epsilon was as effective as chloroplast gamma. The finding that the small CF1 subunits in concert and the beta subunit by itself specifically interacted with the exposed proton channel CF0, qualifies the previous concept of subunit delta acting particularly as a plug to the open CF0 channel. The interactions between the channel and the catalytic portion of the enzyme seem to involve most of the small, and at least beta of the large subunits.