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PubMed2004

Disruption of a specific molecular interaction with a bound lipid affects the thermal stability of the purple bacterial reaction centre.

Relatively little is known about the functions of specific molecular interactions between membrane proteins and membrane lipids. The structural and functional consequences of disrupting a previously identified interaction between a molecule of the diacidic lipid cardiolipin and the purple bacterial reaction centre were examined. Mutagenesis of a highly conserved arginine (M267) that is responsible for binding the head-group of the cardiolipin (to leucine) did not affect the rate of photosynthetic growth, the functional properties of the reaction centre, or the X-ray crystal structure of the complex (determined to a resolution of 2.8 A). However, the thermal stability of the protein was compromised by this mutation, part of the reaction centre population showing an approximately 5 degrees C decrease in melting temperature in response to the arginine to leucine mutation. The crystallised mutant reaction centre also no longer bound detectable amounts of cardiolipin at this site. Taken together, these observations suggest that this particular protein-lipid interaction contributes to the thermal stability of the complex, at least when in detergent micelles. These findings are discussed in the light of proposals concerning the unfolding processes that occur when membrane proteins are heated, and we propose that one function of the cardiolipin is to stabilise the interaction between adjacent membrane-spanning alpha-helices in a region where there are no direct protein-protein interactions.

Calorimetry, Differential Scanning↗
PubMed2006

Specific phospholipid recognition by human immunodeficiency virus type-1 neutralizing anti-gp41 2F5 antibody.

HIV-1 neutralizing monoclonal antibody (Mab) 2F5 recognizes a membrane-partitioning gp41 sequence. Just recently its capacity to react with cardiolipin has been demonstrated. Here, we have studied the specificity of Mab2F5-phospholipid interactions comparing partitioning into lipid bilayers with recognition of molecular species dispersed in solution. Using a liposome-based ELISA we demonstrate a preferential association with cardiolipin bilayers. When different soluble lysoderivatives were compared in their capacity to inhibit Mab2F5 binding to immobilized HIV-1 peptide epitope, only dilysocardiolipin resulted effective in blocking the process. Dilyso-cardiolipin also competed with native-functional gp41 for 2F5 recognition. Thus, our data support specific cardiolipin recognition by 2F5 that is not dependent on lipid bilayer assembly and involves the epitope-binding site. These findings might be of relevance for understanding the molecular basis of HIV-1 immune evasion.

Animals↗
PubMed2002

Disease-specific remodeling of cardiac mitochondria after a left ventricular assist device.

BACKGROUND: Failing hearts can exhibit elements of structural and molecular "reverse remodeling" after support with a left ventricular assist device (LVAD). The present study examined LVAD-induced remodeling of cardiac mitochondria. METHODS: Left ventricular tissue from 20 failing and 21 LVAD-supported hearts, catagorized as ischemic (ICM) or dilated (DCM) cardiomyopathy and four nonfailing hearts were studied. Myocyte mitochondrial ultrastructure was assessed by high-performance liquid chromatography determination of cardiolipin, a specific lipid component of the inner membrane, and its three major molecular species: L4, L3O, and L2O2. RESULTS: Both failing and LVAD-supported hearts exhibited a reduction in cardiolipin content that was independent of the type of cardiomyopathy. However, in failing/ICM hearts, there was a 25% increase in the L4/L3O ratio and a 70% increase in the L4/L2O2 ratio, indicating a change in cardiolipin composition. These alterations were normalized by LVAD support. In sharp contrast, molecular species ratios in DCM hearts were the same as those in nonfailing hearts regardless of whether LVAD support had been used or not. CONCLUSIONS: These data demonstrate LVAD-induced reverse remodeling of myocyte cardiolipin composition in ICM but not DCM hearts.

Adult↗
PubMed1996

Tetraoleoylpyrophosphatidic acid: a four acyl-chain lipid which forms a hexagonal II phase with high curvature.

Tetraoleoylpyrophosphatidic acid (bis phosphatidic acid), when hydrated in aqueous buffer, was shown to form an inverted hexagonal phase using 31P NMR. Low-angle x-ray diffraction provided verification of the formation of this phase in dilute aqueous buffer and in 2 M NaCl and permitted comparison of the tube diameter with that of cardiolipin in 2 M NaCl. By using the water cylinder diameters for tetraoleoylpyrophosphatidic acid, bovine cardiolipin, chloroplast monogalactosyl-diglyceride, and dioleoyl phosphatidylethanolamine as a means of estimating the spontaneous curvatures, tetraoleoylpyro-phosphatidic acid was shown to exhibit the greatest curvature of any of the above lipids, equaled only by the calcium salt of cardiolipin. Inverted micelles of hydrated tetraoleoylpyrophosphatidic acid and of cardiolipin in tetradecane were approximately the diameter of the inverted hexagonal tubes. A rationale is given for the differences.

Animals↗
PubMed2000

Effect of Adriamycin on the boundary lipid structure of cytochrome c oxidase: pico-second time-resolved fluorescence depolarization studies.

The fluorescence dynamics of the dye 3,3'-diethyloxadicarbocyanine iodide (DODCI) was used to probe the microenvironment of cytochrome c oxidase (CcO) and cardiolipin. The dye was partitioned between an aqueous and a hydrophobic phase. The 'bound' and 'free' populations of DODCI could be separated by analysis of the time-resolved fluorescence decay of the dye. The anisotropy decay of the DODCI bound to CcO showed a unique 'dip and rise' shape that was analyzed by a combination of rotational correlation times with time-dependent weight factors for each lifetime component. Rotational dynamics studies revealed the existence of a restricted motion of the dye bound at the enzyme surface. Adriamycin, an anticancer, albeit cardiotoxic drug, was previously proposed to affect the surface structure of CcO, most likely by causing a disorder to the surface lipid arrangement. A drastic change in the rotational correlation time of the dye bound to the enzyme surface was observed, which suggested a depletion of cardiolipin layer due to complexation with the drug. The effect of Adriamycin on cardiolipin was drastic, leading to its phase separation. The present study suggests that the effect of Adriamycin on CcO is primarily a segregation of the cardiolipins.

Algorithms↗
PubMed1999

Lipid peroxidation and alterations to oxidative metabolism in mitochondria isolated from rat heart subjected to ischemia and reperfusion.

Ischemia-reperfusion injury to cardiac myocytes involves membrane damage mediated by oxygen free radicals. Lipid peroxidation is considered a major mechanism of oxygen free radical toxicity in reperfused heart. Mitochondrial respiration is an important source of these reactive oxygen species and hence a potential contributor to reperfusion injury. We have examined the effects of ischemia (30 min) and ischemia followed by reperfusion (15 min) of rat hearts, on the kinetic parameters of cytochrome c oxidase, on the respiratory activities and on the phospholipid composition in isolated mitochondria. Mitochondrial content of malonyldialdheyde (MDA), an index of lipid peroxidation, was also measured. Reperfusion was accompanied by a significant increase in MDA production. Mitochondrial preparations from control, ischemic and reperfused rat heart had equivalent Km values for cytochrome c, although the maximal activity of the oxidase was 25 and 51% less in ischemic and reperfused mitochondria than that of controls. These changes in the cytochrome c oxidase activity were associated to parallel changes in state 3 mitochondrial respiration. The cytochrome aa3 content was practically the same in these three types of mitochondria. Alterations were found in the mitochondrial content of the major phospholipid classes, the most pronounced change occurring in the cardiolipin, the level that decreased by 28 and by 50% as function of ischemia and reperfusion, respectively. The lower cytochrome c oxidase activity in mitochondria from reperfused rat hearts could be almost completely restored to the level of control hearts by exogenously added cardiolipin, but not by other phospholipids nor by peroxidized cardiolipin. It is proposed that the reperfusion-induced decline in the mitochondrial cytochrome c oxidase activity can be ascribed, at least in part, to a loss of cardiolipin content, due to peroxidative attack of its unsaturated fatty acids by oxygen free radicals. These findings may provide an explanation for some of the factors that lead to myocardial reperfusion injury.

Animals↗
PubMed1991

Serum factors affecting the specificity of anticardiolipin antibodies.

The effects were investigated of two pretreatments of human serum and plasma test samples on their subsequent reactivity in the anticardiolipin antibody enzyme-linked immunosorbent assay (ACA-ELISA). The first treatment involved heat inactivation of test samples at 56 degrees C for 30 min, a process sometimes used to inactivate samples from suspected human immunodeficiency virus positive individuals. Such treatment significantly increased the IgG ACA unit/mL values of normal sera, but when this effect was examined further, it was found that the increase in binding occurred on both cardiolipin-coated and uncoated wells and was therefore non-specific. Heat inactivation of sera prior to ACA testing should therefore be avoided. The second treatment involved diluting immunoglobulin (Ig)G and IgM ACA-positive sera in normal human serum (NHS) or newborn calf serum (NCS); sera diluted in NHS showed a significant increase in titre, particularly IgM ACA-positive sera. This phenomenon was found to be due to a serum cardiolipin-binding cofactor which enhances antibody recognition. The cofactor is heat stable and is present in normal sera (male and female) and also in IgG ACA-positive sera. The binding of a human IgM monoclonal antibody to cardiolipin was not affected by the cofactor. The cardiolipin/cofactor complex may represent the optimal autoantigen/autoimmunogen and a re-appraisal, therefore, of the clinical relevance of antibodies to cardiolipin and other negatively charged molecules is warranted.

Animals↗
PubMed2003

Proapoptotic Bid binds to monolysocardiolipin, a new molecular connection between mitochondrial membranes and cell death.

Recent evidence indicates that the mitochondrial lipid cardiolipin may be instrumental in the proapoptotic action of Bcl-2 family proteins on mitochondrial membranes, leading to the release of apoptogenic factors. However, contrasting evidence indicates that progressive loss of cardiolipin occurs during apoptosis. Here we show that Bid, a crucial proapoptotic protein that integrates the action of other Bcl-2 family members, exhibits discrete specificity for metabolites of cardiolipin, especially monolysocardiolipin (MCL). MCL, normally present in the remodelling of mitochondrial lipids, progressively increases in mitochondria during Fas-mediated apoptosis as a by-product of cardiolipin degradation, and also enhances Bid binding to membranes. MCL may thus play a crucial role in connecting lipid metabolism, relocation of Bid to mitochondria and integrated action of Bcl-2 proteins on mitochondrial membranes. We propose that Bid interaction with MCL 'primes' the mitochondrial outer membrane via segregation of lipid domains, facilitating membrane discontinuity and leakage of apoptogenic factors.

Animals↗
PubMed1979

Characterization of lipid-protein interactions in acetylcholinesterase lipoprotein extracted from bovine erythrocytes.

Acetylcholinesterase was released from bovine erythrocytes in hypo-osmotic sodium phosphate buffer. Initially, about 30% of the enzyme was released in a soluble lipoprotein form, and further incubation resulted in the progressive release of the enzyme in a particulate form. Solubilization of the acetylcholinesterase in the particulate fraction with Lubrol WX (2 mg/ml) resulted in the loss of all lipids except a non-exchangeable fraction identified as cardiolipin. Addition of a mixture of erythrocyte phospholipids to the soluble forms and to the Lubrol WX-solubilized enzyme resulted in the formation of particulate forms of the enzyme with increased partial specific volume and Stokes radius, and a break in the Arrhenius plot of the enzyme activity around 20 degrees C. The break in the Arrhenius plot was abolished by treatment of a soluble enzyme preparation with 1.8 M salt (NaCl) in phosphate buffer, conditions that allowed the extraction of cardiolipin from the enzyme by chloroform/methanol. Failure of the high-salt treatment to decrease the Stokes radius made it unlikely that the bound cardiolipin formed a boundary layer or annulus around the protein. It is suggested that cardiolipin is bound to the core of the dimeric protein structure, thereby controlling the acetylcholinesterase activity.

Acetylcholinesterase↗
PubMed2002

Inhibitory effects of acidic phospholipids on the binding of origin-recognition complex to origin DNA.

Origin-recognition complex (ORC), a candidate initiator of chromosomal DNA replication in eukaryotes, shares certain biochemical characteristics with DnaA, the initiator of chromosomal DNA replication in prokaryotes. These similarities include origin-specific DNA binding, ATP binding and ATPase activity. DnaA interacts with acidic phospholipids, such as cardiolipin, and its activity is regulated by these phospholipids. In this study, we examined whether Saccharomyces cerevisiae ORC also interacts with phospholipids. Among the various phospholipids tested, ORC was found to bind specifically to cardiolipin. This binding was inhibited by excess concentrations of salts but unaffected by ATP, adenosine 5'-[gamma-thio]triphosphate or the origin DNA. Cardiolipin weakly inhibited the ATP-binding activity of ORC, whereas it strongly inhibited ORC binding to origin DNA. Acidic phospholipids other than cardiolipin (phosphatidylglycerol and phosphatidylinositol) weakly inhibited ORC binding to origin DNA. Furthermore, total phospholipids extracted from yeast nuclear membranes inhibited ORC binding to origin DNA. We consider that phospholipids may modulate initiation of DNA replication in eukaryotes in a similar manner to that found in prokaryotes.

Adenosine Triphosphatases↗
PubMed2000

Lipid alterations in transient forebrain ischemia: possible new mechanisms of CDP-choline neuroprotection.

We have previously demonstrated that cytidine 5'-diphosphocholine (CDP-choline or citicoline) attenuated arachidonic acid (ArAc) release and provided significant protection for the vulnerable hippocampal CA(1) neurons of the cornu ammonis after transient forebrain ischemia of gerbil. ArAc is released by the activation of phospholipases and the alteration of phosphatidylcholine (PtdCho) synthesis. Released ArAc is metabolized by cyclooxygenases/lipoxygenases to form eicosanoids and reactive oxygen species (ROS). ROS contribute to neurotoxicity through generation of lipid peroxides and the cytotoxic byproducts 4-hydroxynonenal and acrolein. ArAc can also stimulate sphingomyelinase to produce ceramide, a potent pro-apoptotic agent. In the present study, we examined the changes and effect of CDP-choline on ceramide and phospholipids including PtdCho, phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer), sphingomyelin, and cardiolipin (an exclusive inner mitochondrial membrane lipid essential for electron transport) following ischemia/1-day reperfusion. Our studies indicated significant decreases in total PtdCho, PtdIns, PtdSer, sphingomyelin, and cardiolipin and loss of ArAc from PtdEtn in gerbil hippocampus after 10-min forebrain ischemia/1-day reperfusion. CDP-choline (500 mg/kg i.p. immediately after ischemia and at 3-h reperfusion) significantly restored the PtdCho, sphingomyelin, and cardiolipin levels as well as the ArAc content of PtdCho and PtdEtn but did not affect PtdIns and PtdSer. These data suggest multiple beneficial effects of CDP-choline: (1) stabilizing the cell membrane by restoring PtdCho and sphingomyelin (prominent components of outer cell membrane), (2) attenuating the release of ArAc and limiting its oxidative metabolism, and (3) restoring cardiolipin levels.

Animals↗
PubMed2003

A simple method to discriminate between beta2-glycoprotein I- and prothrombin-dependent lupus anticoagulants.

Lupus anticoagulants (LAC) are a heterogeneous group of autoantibodies that prolong phospholipid-dependent clotting assays. The autoantibodies that cause LAC activity are predominantly directed against beta2-glycoprotein I (beta2GPI) or prothrombin. In the present study, we describe a method to differentiate between LAC caused by antibodies directed against beta2GPI or prothrombin. Monoclonal antibodies, affinity purified patient antibodies, and selected patient samples were used to show that in an aPTT-based clotting assay (PTT-LA; Diagnostica Stago), the use of cardiolipin vesicles in the neutralization procedure discriminates between beta2GPI- or prothrombin-dependent LAC activities. Addition of cardiolipin vesicles shortened the prolonged clotting time caused by anti-beta2GPI antibodies with LAC activity, whereas this procedure further prolonged clotting times caused by antiprothrombin antibodies with LAC activity. In contrast, addition of phosphatidylcholine/phosphatidylserine vesicles corrected prolonged clotting times caused by either anti-beta2GPI or antiprothrombin antibodies with LAC activity. The effects of cardiolipin (CL) on beta2GPI-induced LAC activity were specific for contact activation mediated clotting assays. Possible explanations for these findings are the relatively high affinity of beta2GPI for cardiolipin, as determined by surface plasmon resonance analysis, and inhibition by anti-beta2GPI antibodies of the CL-induced prolongation of the PTT-LA.

Autoantibodies↗
PubMed2006

A Drosophila model of Barth syndrome.

Barth syndrome is an X-linked disease presenting with cardiomyopathy and skeletal muscle weakness. It is caused by mutations in tafazzin, a putative acyl transferase that has been associated with altered metabolism of the mitochondrial phospholipid cardiolipin. To investigate the molecular basis of Barth syndrome, we created Drosophila melanogaster mutants, resulting from imprecise excision of a P element inserted upstream of the coding region of the tafazzin gene. Homozygous flies for that mutation were unable to express the full-length isoform of tafazzin, as documented by RNA and Western blot analysis, but two shorter tafazzin transcripts were still present, although the expression levels of their encoded proteins were too low to be detectable by Western blotting. The tafazzin mutation caused an 80% reduction of cardiolipin and a diversification of its molecular composition, similar to the changes seen in Barth patients. Other phospholipids, like phosphatidylcholine and phosphatidylethanolamine, were not affected. Flies with the tafazzin mutation showed a reduced locomotor activity, measured in flying and climbing assays, and their indirect flight muscles displayed frequent mitochondrial abnormalities, mostly in the cristae membranes. Thus, tafazzin mutations in Drosophila generated a Barth-related phenotype, with the triad of abnormal cardiolipin, pathologic mitochondria, and motor weakness, suggesting causal links between these findings. We conclude that a lack of full-length tafazzin is responsible for the cardiolipin deficiency, which is integral to the disease mechanism, leading to mitochondrial myopathy.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1975

Antigen mobility in membranes and complement-medical immune attack.

The complement fixing activity of liposomes containing cholesterol, dimyristoylphosphatidylcholine (or dipalmitoylphosphatidylcholine), and 3 mol % of cardiolipin has been studied as a function of cholesterol concentration by use of human syphilitic serum containing cardiolipin-specific (Wasserman) antibodies. It is found that complement fixation increases rapidly for cholesterol concentrations above 35 mol %. Spin label studies have been used to study the incorporation of cardiolipin in the relatively rigid phase of binary mixtures of cholesterol and dimyristolphosphatidycholine (or dipalmitoylphosphatidylcholine). It is concluded that cardiolipin is included in such a phase of these lipids for cholesterol concentrations above 35 mol %. These results indicate that a relatively rigid lateral distribution of this monovalent antigen in the plane of the membrane facilitates complement fixation and concomitant complement-mediated membrane damage.

Animals↗
PubMed2000

Identification of amino acids involved in the functional interaction between DnaA protein and acidic phospholipids.

DnaA protein, the initiator of chromosomal DNA replication in Escherichia coli, seems to be regulated through its binding to acidic phospholipids, such as cardiolipin. In our previous paper (Hase, M., Yoshimi, T., Ishikawa, Y., Ohba, A., Guo, L., Mima, S., Makise, M., Yamaguchi, Y., Tsuchiya, T., and Mizushima, T. (1998) J. Biol. Chem. 273, 28651-28656), we found that mutant DnaA protein (DnaA431), in which three basic amino acids (Arg(360), Arg(364), and Lys(372)) were mutated to acidic amino acids showed a decreased ability to interact with cardiolipin in vitro, suggesting that DnaA protein binds to cardiolipin through an ionic interaction. In this study, we construct three mutant dnaA genes each with a single mutation and examined the function of the mutant proteins in vitro and in vivo. All mutant proteins maintained activities for DNA replication and ATP binding. A mutant protein in which Lys(372) was mutated to Glu showed the weakest interaction with cardiolipin among these three mutant proteins. Thus, Lys(372) seems to play an important role in the interaction between DnaA protein and acidic phospholipids. Plasmid complementation analyses revealed that all these mutant proteins, including DnaA431 could function as an initiator for chromosomal DNA replication in vivo.

Adenosine Diphosphate↗
PubMed2000

Molecular mechanism for functional interaction between DnaA protein and acidic phospholipids: identification of important amino acids.

DnaA protein, the initiator of chromosomal DNA replication in Escherichia coli, seems to be reactivated from the ADP-bound form to its ATP-bound form through stimulation of ADP release by acidic phospholipids such as cardiolipin. We previously reported that two potential amphipathic helices (Lys-327 to Ile-344 and Asp-357 to Val-374) of DnaA protein are involved in the functional interaction between DnaA and cardiolipin. In relation to one of these helices (Asp-357 to Val-374), we demonstrated that basic amino acids in the helix, especially Lys-372, are vital for this interaction. In this study, we have identified an amino acid in the second potential amphipathic helix (Lys-327 to Ile-344), which would also appear to be involved in the interaction. We constructed three mutant dnaA genes with a single mutation (dnaAR328E, dnaAR334E, and dnaAR342E) and examined the function of the mutant proteins. DnaAR328E, but not DnaAR334E and DnaAR342E, was found to be more resistant to inhibition of its ATP binding activity by cardiolipin than the wild-type protein. The stimulation of ADP release from DnaAR328E by cardiolipin was also weaker than that observed with the other mutants and the wild-type protein. These results suggest that Arg-328 of DnaA protein is involved in the functional interaction of this protein with acidic phospholipids. We propose that acidic phospholipids bind to two basic amino acid residues (Arg-328 and Lys-372) of DnaA protein and change the higher order structure of its ATP-binding pocket, which in turn stimulates the release of ADP from the protein.

Adenine↗
PubMed2006

The enzymatic function of tafazzin.

Tafazzin is a putative enzyme that is involved in cardiolipin metabolism, it may carry mutations responsible for Barth syndrome. To identify the biochemical reaction catalyzed by tafazzin, we expressed the full-length isoform of Drosophila melanogaster tafazzin in a baculovirus-Sf9 insect cell system. Tafazzin expression induced a new enzymatic function in Sf9 cell mitochondria, namely 1-palmitoyl-2-[14C]linoleoyl-phosphatidylcholine:monolysocardiolipin linoleoyltransferase. We also found evidence for the reverse reaction, because tafazzin expression caused transfer of acyl groups from phospholipids to 1-[14C]palmitoyl-2-lyso-phosphatidylcholine. An affinity-purified tafazzin construct, tagged with the maltose-binding protein, catalyzed both forward and reverse transacylations between cardiolipin and phosphatidylcholine, but was unable to utilize CoA or acyl-CoA as substrates. Whereas tafazzin supported transacylations between various phospholipid-lysophospholipid pairs, it showed the highest rate for the phosphatidylcholine-cardiolipin transacylation. Transacylation activities were about 10-fold higher for linoleoyl groups than for oleoyl groups, and they were negligible for arachidonoyl groups. The data show that Drosophila tafazzin is a CoA-independent, acyl-specific phospholipid transacylase with substrate preference for cardiolipin and phosphatidylcholine.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1991

Phosphatidyltransferase activity in Bacillus megaterium.

Phosphatidyl transfer between phosphatidylethanolamine, phosphatidylglycerol or phosphatidylserine as donors and primary hydroxyl acceptors including ethanolamine, glycerol, serine and Triton X-100 has been shown to be catalysed by membrane particles derived from Bacillus megaterium strains ATCC 13632 and ATCC 14581. The rate of cardiolipin synthesis from phosphatidylglycerol in the presence of ethanolamine was an order of magnitude greater than that of phosphatidylethanolamine formation. Cardiolipin synthesis from phosphatidylethanolamine in the presence of glycerol was also observed, and was 1.5-fold greater than the formation of phosphatidylglycerol. Similar heat lability, effects of pH and of Triton X-100 for phosphatidyl transfer and cardiolipin synthesis indicate that both reactions were catalysed by cardiolipin synthase.

Bacillus megaterium↗