Interactions between the oligomycin sensitivity conferring protein (OSCP) and beef heart mitochondrial F1-ATPase. 2. Identification of the interacting F1 subunits by cross-linking

Interactions between oligomycin sensitivity conferring protein (OSCP) and subunits of beef heart mitochondrial F1-ATPase have been explored by cross-linking at an OSCP/F1 molar ratio close to 1 to ensure specific high-affinity binding of OSCP to F1 [see Dupuis et al. [Dupuis, A., Issartel, J.-P., Lunardi, J., Satre, M., & Vignais, P.V. (1985) Biochemistry (preceding paper in this issue)]]. Cross-links between F1 subunits and OSCP were established by means of two zero length cross-linkers, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide and N-(ethoxycarbonyl)-2-ethoxydihydroquinoline. The cross-linked products were separated by sodium dodecyl suflate-polyacrylamide gel electrophoresis. Coomassie blue staining revealed two cross-linked products of Mr 75 000 and 80 000 which could result from the binding of OSCP to the alpha and beta subunits of F1. Definite identification of the cross-linked products was achieved by chemical labeling with specific radiolabeled reagents and by blotting on nitrocellulose filters followed by immunocharacterization with anti-alpha, anti-beta, and anti-OSCP antibodies. OSCP was found to cross-link with the alpha and beta subunits of F1.     

The effect of nucleotides and mitochondrial chaperonin 10 on the structure and chaperone activity of mitochondrial chaperonin 60.

Mitochondrial chaperonins are necessary for the folding of newly imported and stress-denatured mitochondrial proteins. The goal of this study was to investigate the structure and function of the mammalian mitochondrial chaperonin system. We present evidence that the 60 kDa chaperonin (mt-cpn60) exists in solution in dynamic equilibrium between monomers, heptameric single rings and double-ringed tetradecamers. In the presence of ATP and the 10 kDa cochaperonin (mt-cpn10), the formation of a double ring is favored. ADP at very high concentrations does not inhibit malate dehydrogenase refolding or ATP hydrolysis by mt-cpn60 in the presence of mt-cpn10. We propose that the cis (mt-cpn60)14.nucleotide.(mt-cpn10)7 complex is not a stable species and does not bind ADP effectively at its trans binding site.     

alpha, beta-Bidentate CrADP abolishes the negative cooperativity of yeast mitochondrial F1-ATPase

The hydrolysis of MgATP and MgITP by mitochondrial F1-ATPase from Saccharomyces cerevisiae is competitively inhibited by alpha, beta-CrADP, alpha, beta, gamma-CrATP and beta, gamma-CrATP. The apparent K1 values of the three complexes are in the range of the half-saturating MgATP concentration. The negative cooperativity (nH = 0.7) of MgATP hydrolysis is totally abolished by alpha, beta-CrADP (nH = 1.0), while it is not affected by the CrATP. It is concluded that alpha, beta-CrADP binds exclusively at the regulatory site and that CrATP binds exclusively to the catalytic site.     

The delta'-subunit of higher plant six-subunit mitochondrial F1-ATPase is homologous to the delta-subunit of animal mitochondrial F1-ATPase.

Mitochondrial F1-ATPases purified from several dicotyledonous plants contain six different subunits of alpha, beta, gamma, delta, delta' and epsilon. Previous N-terminal amino acid sequence analyses indicated that the gamma-, delta-, and epsilon-subunits of the sweet potato mitochondrial F1 correspond to the gamma-subunit, the oligomycin sensitivity-conferring protein and the epsilon-subunit of animal mitochondrial F1F0 complex (Kimura, T., Nakamura, K., Kajiura, H., Hattori, H., Nelson, N., and Asahi, T. (1989) J. Biol. Chem. 264, 3183-3186). However, the N-terminal amino acid sequence of the delta'-subunit did not show any obvious homologies with known protein sequences. A cDNA clone for the delta'-subunit of the sweet potato mitochondrial F1 was identified by oligonucleotide-hybridization selection of a cDNA library. The 1.0-kilobase-long cDNA contained a 600-base pair open reading frame coding for a precursor for the delta'-subunit. The precursor for the delta'-subunit contained N-terminal presequence of 21-amino acid residues. The mature delta'-subunit is composed of 179 amino acids and its sequence showed similarities of about 31-36% amino acid positional identity with the delta-subunit of animal and fungal mitochondrial F1 and about 18-25% with the epsilon-subunit of bacterial F1 and chloroplast CF1. The sweet potato delta'-subunit contains N-terminal sequence of about 45-amino acid residues that is absent in other related subunits. It is concluded that the six-subunit plant mitochondrial F1 contains the subunit that is homologous to the oligomycin sensitivity-conferring protein as one of the component in addition to five subunits that are homologous to subunits of animal mitochondrial F1.     

Availability to monoclonal antibodies of antigenic sites of the alpha and beta subunits in active, denatured or membrane-bound mitochondrial F1-ATPase

The binding of five monoclonal antibodies to mitochondrial F1-ATPase has been studied. Competition experiments between monoclonal antibodies demonstrate that these antibodies recognize four different antigenic sites and provide information on the proximity of these sites. The accessibility of the epitopes has been compared for F1 integrated in the mitochondrial membrane, for purified beta-subunit and for purified F1 maintained in its active form by the presence of nucleotides or inactivated either by dilution in the absence of ATP or by urea treatment. The three anti-beta monoclonal antibodies bound more easily to the beta-subunit than to active F1, and recognized equally active F1 and F1 integrated in the membrane, indicating that their antigenic sites are partly buried similarly in purified or membrane-bound F1 and better exposed in the isolated beta-subunit. In addition, unfolding F1 by urea strongly increased the binding of one anti-beta monoclonal antibody (14 D5) indicating that this domain is at least partly shielded inside the beta-subunit. One anti-alpha monoclonal antibody (20 D6) bound poorly to F1 integrated in the membrane, while the other (7 B3) had a higher affinity for F1 integrated in the membrane than for soluble F1. Therefore, 20 D6 recognizes an epitope of the alpha-subunit buried inside F1 integrated in the membrane, while 7 B3 binds to a domain of the alpha-subunit well exposed at the surface of the inner face of the mitochondrial membrane.     

Characterization of a stable, reactivatable complex between chaperonin 60 and mitochondrial rhodanese.

Efficient formation of the cpn60-rhodanese complex can be achieved by mixing unfolded rhodanese with excess cpn60 at low temperature. By employing these conditions, a stable and highly reactivatable complex is formed. The complex is not formed when native enzyme is used. Concentrations of NaCl, as high as 0.75 M, do not have any effect on the formation or disruption of the binary complex. cpn60-bound rhodanese contains an exposed hydrophobic surface, as detected by the binding of the fluorescent reporter, 1-anilinonaphthalene-8-sulfonic acid. The intrinsic fluorescence of cpn60-bound rhodanese reports that the average tryptophan is in an intermediate environment between that found in unfolded and native states. This form of rhodanese has an accessibility to quenching by acrylamide or iodide that is intermediate between the unfolded and native forms of the enzyme. Protease susceptibility studies show that rhodanese bound to cpn60 exhibits a trypsin digestion pattern similar to the native enzyme, although it is more rapidly proteolyzed. The results suggest that the conformation of cpn60-bound rhodanese resembles a native-like conformation, but with increased flexibility. Further, only intact rhodanese or enzyme lacking its N-terminal sequence can interact with cpn60 and form a stable binary complex. The protein fragment corresponding to the rhodanese N-terminal sequence did not form part of a stable complex with cpn60.     

The two mammalian mitochondrial stress proteins, grp 75 and hsp 58, transiently interact with newly synthesized mitochondrial proteins.

In mammalian cells, two of the so-called heat shock (hsp) or stress proteins are components of the mitochondria. One of these, hsp 58, is a member of the bacterial GroEL family, whereas the other, glucose-regulated protein (grp) 75, represents a member of the hsp 70 family of stress proteins. Owing to previous studies implicating a role for both the hsp 70 and GroEL families in facilitating protein maturation events, we used the method of native immunoprecipitation to examine whether hsp 58 and grp 75 might interact with other proteins of the mitochondria. In cells pulse-labeled with [35S]-methionine, a significant number of newly synthesized mitochondrial proteins co-precipitated with either hsp 58 or grp 75. Such interactions appeared transient. For example, providing the pulse-labeled cells a subsequent chase period in the absence of radiolabel resulted in a reduction of co-precipitating proteins. If the pulse-chase labeling experiments were performed in the presence of an amino acid analogue, somewhat different results were obtained. Specifically, although many of the newly synthesized and analogue-containing proteins again were observed to co-precipitate with grp 75, the interactions did not appear transient, but instead were stable. Under steady-state labeling conditions, we also observed a portion of hsp 58 and grp 75 in an apparent complex with one another. On addition of ATP, the complex was dissociated. Accompanying this dissociation was the concomitant autophosphorylation of grp 75. On the basis of these observations, as well as previous studies examining the structure/function of the hsp 70 and GroEL proteins, we suspect that both hsp 58 and grp 75 interact with and facilitate the folding and assembly of proteins as they enter into the mitochondria.     

Identification of the subunits of F1F0-ATPase from bovine heart mitochondria.

An oligomycin-sensitive F1F0-ATPase isolated from bovine heart mitochondria has been reconstituted into phospholipid vesicles and pumps protons. this preparation of F1F0-ATPase contains 14 different polypeptides that are resolved by polyacrylamide gel electrophoresis under denaturing conditions, and so it is more complex than bacterial and chloroplast enzymes, which have eight or nine different subunits. The 14 bovine subunits have been characterized by protein sequence analysis. They have been fractionated on polyacrylamide gels and transferred to poly(vinylidene difluoride) membranes, and N-terminal sequences have been determined in nine of them. By comparison with known sequences, eight of these have been identified as subunits beta, gamma, delta, and epsilon, which together with the alpha subunit form the F1 domain, as the b and c (or DCCD-reactive) subunits, both components of the membrane sector of the enzyme, and as the oligomycin sensitivity conferral protein (OSCP) and factor 6 (F6), both of which are required for attachment of F1 to the membrane sector. The sequence of the ninth, named subunit e, has been determined and is not related to any reported protein sequence. The N-terminal sequence of a tenth subunit, the membrane component A6L, could be determined after a mild acid treatment to remove an alpha-N-formyl group. Similar experiments with another membrane component, the a or ATPase-6 subunit, caused the protein to degrade, but the protein has been isolated from the enzyme complex and its position on gels has been unambiguously assigned. No N-terminal sequence could be derived from three other proteins. The largest of these is the alpha subunit, which previously has been shown to have pyrrolidonecarboxylic acid at the N terminus of the majority of its chains. The other two have been isolated from the enzyme complex; one of them is the membrane-associated protein, subunit d, which has an alpha-N-acetyl group, and the second, surprisingly, is the ATPase inhibitor protein. When it is isolated directly from mitochondrial membranes, the inhibitor protein has a frayed N terminus, with chains starting at residues 1, 2, and 3, but when it is isolated from the purified enzyme complex, its chains are not frayed and the N terminus is modified. Previously, the sequences at the N terminals of the alpha, beta, and delta subunits isolated from F1-ATPase had been shown to be frayed also, but in the F1F0 complex they each have unique N-terminal sequences.(ABSTRACT TRUNCATED AT 400 WORDS)     

Topography of the subunits of Micrococcus lysodeikticus F1-ATPase

Summary The combined use of proteolytic digestion and lactoperoxidase catalyzed labelling with [¹²⁵I] applied to membrane-bound or soluble pure F₁-ATPase from Micrococcus lysodeikticus has allowed us to establish the topography of its , , and subunits within the protein molecule and with respect to the plane of the membrane.The subunit is most externally located to the membrane bilayer looking towards the cytoplasmic face, a position consistent with its proposed catalytic role. The and subunits lie in an intermediate layer between the subunits and the membrane, in which the subunit occupies a central position within the F₁-ATPase molecule in contact with the subunit. The subunit appears to be tightly bound to the F₀ component of the ATPase complex, probably buried in the membrane bilayer. A molecular arrangement of M. lysodeikticus ATPase is proposed that, taking into account the subunit stoichiometry _{3 3 2 2} (MW 420 000), accommodates the role assigned to each subunit and most, if not all, the known properties of this bacterial energy-transducing protein.     

Evidence for three alpha subunits in one molecule of F1-ATPase from thermophilic bacterium PS3.

The numbers of sulfhydryl residues in F₁-ATPase of thermophilic bacterium PS3 and its isolated subunits were analyzed with Ellman's reagent. This F₁-ATPase contained three sulfhydryl residues and no disulfide bridge. Of the five kinds of subunits of the F₁-ATPase, only the α subunit contained one sulfhydryl residue. So there are three α subunits in one molecule of the F₁-ATPase.     

The alpha subunit of a plant mitochondrial F1-ATPase is translated in mitochondria

The mitochondrial F1-ATPase from bean (Vicia faba L.) was solubilized by a chloroform treatment of mitochondrial membranes and purified by centrifugation on a glycerol gradient. The active fraction contained 5 subunits: alpha (Mr = 52,000), beta (Mr = 51,000), gamma (Mr = 34,000), delta (Mr = 23,800), and epsilon (Mr = 22,900). Purified coupled mitochondria were incubated in the presence of [ 35S ]methionine and malate to allow mitochondrial translation to occur. The largest labeled polypeptide (Mr = 52,000) was present in the chloroform extract, co-sedimented with the F1-ATPase on glycerol gradient and co-migrated with the alpha subunit upon two-dimensional electrophoresis. The results indicate that the alpha subunit of bean mitochondrial ATPase is translated on mitoribosomes, in contrast to the situation in other organisms.     

A newly synthesized protein interacts with GroES on the surface of chaperonin GroEL.

To facilitate folding and assembly of different proteins, chaperonin GroEL requires the presence of its helper protein GroES. Using a photochemical cross-linking approach, we show that GroES and newly synthesized pre-beta-lactamase (pre-beta lac) contact with each other only within the ternary complex with GroEL. Possibly owing to this contact GroES is able to directly influence the pre-beta lac/GroEL interaction. Furthermore, the cross-linking of pre-beta lac to GroES suggests that the binding of the protein ligands to GroEL occurs near the GroES binding site, known to be in the central hole space of GroEL.     

Modifiers of the oligomycin sensitivity of the mitochondrial F1F0-ATPase

The mitochondrial F₁F₀ complex is highly sensitive to macrolide antibiotics and especially targeted by oligomycins. These compounds bind to the membrane-embedded sector F₀ and block proton conductance through the inner membrane, thus inhibiting both ATP synthesis and hydrolysis. Oligomycin sensitivity is universally recognized as a clue of the functional integrity and matching between F₀ and F₁. Since oligomycin binding implies multiple interactions with amino acid residues of F₀, amino acid substitutions often affect the inhibition efficiency. Moreover, variegated factors spanning from membrane properties to xenobiotic incorporation and detachment of the oligomycin-insensitive F₁ sector can alter the oligomycin sensitivity of the enzyme complex. The overview on the multiple factors involved strengthens the link between altered oligomycin sensitivity and physiopathological conditions associated with defective ATPases. An improved understanding of the mechanisms involved may also favor drug design to counteract oxidative damage, which stems from most mitochondrial dysfunctions.     

Ni-chelate-affinity purification and crystallization of the yeast mitochondrial F1-ATPase

The yeast mitochondrial ATPase has been genetically modified to include a His(6) Ni-affinity tag on the amino end of the mature beta-subunit. The modified beta-subunit is imported into the mitochondrion, properly processed to the mature form, and assembled into a mature and fully active ATP synthase. The F(1)-ATPase has been purified from submitochondrial particles after release from the membrane with chloroform, followed by Ni-chelate-affinity and gel filtration chromatography. The final enzyme is a homogeneous preparation with full activity and no apparent degradation products. This enzyme preparation has been used to obtain crystals that diffract to better than 2.8 A resolution.     

Identification of F0 subunits in the rat liver mitochondrial F0F1-ATP synthase.

In order to identify the subunits constituting the rat liver F0F1-ATP synthase, the complex prepared by selective extraction from the mitochondrial membranes with a detergent followed by purification on a sucrose gradient has been compared to that obtained by immunoprecipitation with an anti-F1 serum. The subunits present in both preparations that are assumed to be authentic components of the complex have been identified. The results show that the total rat liver F0F1-ATP synthase contains at least 13 different proteins, seven of which can be attributed to F0. The following F0 subunits have been identified: the subunit b (migrating as a 24 kDa band in SDS-PAGE), the oligomycin-sensitivity-conferring protein (20 kDa), and F6 (9 kDa) that have N-terminal sequences homologous to the beef-heart ones; the mtDNA encoded subunits 6 (20 kDa) and 8 (less than 7 kDa) that can be synthesized in isolated mitochondria; an additional 20 kDa protein that could be equivalent to the beef heart subunit d.