Photooxidative and spectral studies on cytochrome c. Conformational changes induced by binding of cardiolipin

Mitochondrial dysfunction, AMPK activation and peroxisomal metabolism: A coherent scenario for non-canonical 3-methylglutaconic acidurias

The occurrence of 3-methylglutaconic aciduria (3-MGA) is a well understood phenomenon in leucine oxidation and ketogenesis disorders (primary 3-MGAs). In contrast, its genesis in non-canonical (secondary) 3-MGAs, a growing-up group of disorders encompassing more than a dozen of inherited metabolic diseases, is a mystery still remaining unresolved for three decades. To puzzle out this anthologic problem of metabolism, three clues were considered: (i) the variety of disorders suggests a common cellular target at the cross-road of metabolic and signaling pathways, (ii) the response to leucine loading test only discriminative for primary but not secondary 3-MGAs suggests these latter are disorders of extramitochondrial HMG-CoA metabolism as also attested by their failure to increase 3-hydroxyisovalerate, a mitochondrial metabolite accumulating only in primary 3-MGAs, (iii) the peroxisome is an extramitochondrial site possessing its own pool and displaying metabolism of HMG-CoA, suggesting its possible involvement in producing extramitochondrial 3-methylglutaconate (3-MG). Following these clues provides a unifying common basis to non-canonical 3-MGAs: constitutive mitochondrial dysfunction induces AMPK activation which, by inhibiting early steps in cholesterol and fatty acid syntheses, pipelines cytoplasmic acetyl-CoA to peroxisomes where a rise in HMG-CoA followed by local dehydration and hydrolysis may lead to 3-MGA yield. Additional contributors are considered, notably for 3-MGAs associated with hyperammonemia, and to a lesser extent in CLPB deficiency. Metabolic and signaling itineraries followed by the proposed scenario are essentially sketched, being provided with compelling evidence from the literature coming in their support.

Peroxidase activity and structural transitions of cytochrome c bound to cardiolipin-containing membranes

During apoptosis, cytochrome c (cyt c) is released from intermembrane space of mitochondria into the cytosol where it triggers the caspase-dependent machinery. We discovered that cyt c plays another critical role in early apoptosis as a cardiolipin (CL)-specific oxygenase to produce CL hydroperoxides required for release of pro-apoptotic factors [Kagan, V. E., et al. (2005) Nat. Chem. Biol. 1, 223-232]. We quantitatively characterized the activation of peroxidase activity of cyt c by CL and hydrogen peroxide. At low ionic strength and high CL/cyt c ratios, peroxidase activity of the CL/cyt c complex was increased >50 times. This catalytic activity correlated with partial unfolding of cyt c monitored by Trp(59) fluorescence and absorbance at 695 nm (Fe-S(Met(80)) band). The peroxidase activity increase preceded the loss of protein tertiary structure. Monounsaturated tetraoleoyl-CL (TOCL) induced peroxidase activity and unfolding of cyt c more effectively than saturated tetramyristoyl-CL (TMCL). TOCL/cyt c complex was found more resistant to dissociation by high salt concentration. These findings suggest that electrostatic CL/cyt c interactions are central to the initiation of the peroxidase activity, while hydrophobic interactions are involved when cyt c's tertiary structure is lost. In the presence of CL, cyt c peroxidase activity is activated at lower H(2)O(2) concentrations than for isolated cyt c molecules. This suggests that redistribution of CL in the mitochondrial membranes combined with increased production of H(2)O(2) can switch on the peroxidase activity of cyt c and CL oxidation in mitochondria-a required step in execution of apoptosis.

Interaction of horse heart cytochrome c with lipid bilayer membranes: effects on redox potentials

Cyclic voltammetry has been used to study the effects of interactions between horse cytochrome c and solid-supported planar lipid membranes, comprised of either egg phosphatidylcholine (PC) or PC plus 20 mol.% cardiolipin (CL), on the redox potential and the electrochemical electron transfer rate between the protein and a semiconductor electrode. Experiments were performed over a wide range of cytochrome c concentrations (0-440 microM) at low (20 mM) and medium (160 mM) ionic strengths. Three types of electrochemical behavior were observed, which varied as a function of the experimental conditions. At very low cytochrome c concentration (approximately 0.1 microM), and under conditions where electrostatic forces dominated the protein-lipid membrane interaction (i.e., low ionic strength with membranes containing CL), a redox potential (approximately 265 mV) and an electrochemical electron transfer rate constant (0.09 s[-1])were obtained which compare well with those measured in other laboratories using a variety of different chemical modifications of the working electrode. Two other electrochemical signals (not reported with chemically modified electrodes) were also observed to occur at higher cytochrome c concentrations with this membrane system, as well as with two other systems (membranes containing CL under medium ionic strength conditions, and PC only at low ionic strength). These involved positive shifts of the cytochrome c redox potential (by 40 and 60 mV) and large decreases in the electron transfer rate (to 0.03 and 0.003 s[-1]). The observations can be rationalized in terms of a structural model of the cytochrome c-membrane interaction, in which association involves both electrostatic and hydrophobic forces and results in varying degrees of insertion of the protein into the hydrophobic interior of the membrane.

Reversibility of the binding of cytochrome c to liposomes. Implications for lipid-protein interactions

Studies on the membrane binding of cytochrome c revealed liposome-associated and soluble cytochrome c not to be in rapid equilibrium. In brief, cytochrome c attached to pyrene phospholipid-labeled, fluorescent liposomes containing either 17.6 mol % cardiolipin (CL) or 30 mol % egg phosphatidylglycerol (PG) is practically not at all or very slowly, respectively, detached by a subsequently added excess (up to 20-fold) of nonlabeled liposomes containing these acidic lipids. Cytochrome c was fully dissociated from PG-containing liposomes by increasing the ionic strength by NaCl, whereas dissociation from CL-containing membranes was less complete, presumably because of the scavenging of the protein within inverted intramembrane micelles. Importantly, the apparent irreversibility of the binding of cytochrome c to liposomes is strongly dependent on the structure of the acidic phospholipid. Cytochrome c bound to lyso-PG/PC liposomes could be dissociated with an excess of nonlabeled PG-containing liposomes. Cytochrome c was also efficiently bound to membranes containing the negatively charged dicetylphosphate yet could be readily dissociated by nonlabeled PG-containing liposomes. We conclude both proper geometry of the phosphate group and the presence of two acyl chains to be required for the tight binding of cytochrome c to acidic phospholipids. These data provide evidence for the membrane association of cytochrome c by an acidic phospholipid in the extended conformation (Kinnunen, P. K. J., Köiv, A., Lehtonen, J. Y. A., Rytömaa, M., and Mustonen, P. (1994) Chem. Phys. Lipids 73, 181-207) in which one of the acyl chains of the lipid becomes accommodated within a hydrophobic cavity of the protein. Based on the crystal structure of cytochrome c we putatively assign the invariant Asn-52 (horse heart cytochrome c) as the site liganding the protonated phosphate of the lipid, whereas Lys-72 and -73 should bind the deprotonated form.

Lipid dynamics and peripheral interactions of proteins with membrane surfaces

A large body of evidence strongly indicates biomembranes to be organized into compositionally and functionally specialized domains, supramolecular assemblies, existing on different time and length scales. For these domains and intimate coupling between their chemical composition, physical state, organization, and functions has been postulated. One important constituent of biomembranes are peripheral proteins whose activity can be controlled by non-covalent binding to lipids. Importantly, the physical chemistry of the lipid interface allows for a rapid and reversible control of peripheral interactions. In this review examples are provided on how membrane lipid (i) composition (i.e., specific lipid structures), (ii) organization, and (iii) physical state can each regulate peripheral binding of proteins to the lipid surface. In addition, a novel and efficient mechanism for the control of the lipid surface association of peripheral proteins by [Ca2+], lipid composition, and phase state is proposed. The phase state is, in turn, also dependent on factors such as temperature, lateral packing, presence of ions, metabolites and drugs. Confining reactions to interfaces allows for facile and cooperative large scale integration and control of metabolic pathways due to mechanisms which are not possible in bulk systems.

The interaction of horse heart cytochrome c with phospholipid bilayers. Structural and dynamic effects

The interaction of cytochrome c with phospholipid bilayers is reviewed. Special emphasis is given to the structural and dynamic perturbations induced, either in the membrane lipid component or protein itself, by the lipid-protein interaction. The lipid-induced perturbations in the structure of cytochrome c involve: i) conformational changes in and around the heme crevice, converting the heme iron to a high-spin state: and ii) a destabilisation/loosening of the overall tertiary and secondary structure. This highly mobile, partially unfolded intermediate of cytochrome c has a remarkable resemblance to partially folded membrane-bound intermediates of the precursor protein. The functional implications of lipid-protein intermediates for (apo) cytochrome c in (protein-translocation) electron-transfer are discussed.

Reversible unfolding of cytochrome c upon interaction with cardiolipin bilayers. 2. Evidence from phosphorus-31 NMR measurements

31P NMR measurements were conducted to determine the structural and chemical environment of beef heart cardiolipin when bound to cytochrome c. 31P NMR line shapes infer that the majority of lipid remains in the bilayer state and that the average conformation of the lipid phosphate is not greatly affected by binding to the protein. An analysis of the spin-lattice (T1) relaxation times of hydrated cardiolipin as a function of temperature describes a T1 minimum at around 25 degrees C which leads to a correlation time for the phosphates in the lipid headgroup of 0.71 ns. The relaxation behavior of the protein-lipid complex was markedly different, showing a pronounced enhancement in the phosphorus spin-lattice relaxation rate. This effect of the protein increased progressively with increasing temperature, giving no indication of a minimum in T1 up to 75 degrees C. The enhancement in lipid phosphorus T1 relaxation was observed with protein in both oxidation states, being somewhat less marked for the reduced form. The characteristics of the T1 effects and the influence of the protein on other relaxation processes determined for the lipid phosphorus (spin-spin relaxation and longitudinal relaxation in the rotating frame) point to a strong paramagnetic interaction from the protein. A comparison with the relaxation behavior of samples spinning at the "magic angle" was also consistent with this mechanism. The results suggest that cytochrome c reversibly denatures on complexation with cardiolipin bilayers, such that the electronic ground state prevailing in the native structure of both oxidized and reduced protein can convert to high-spin states with greater magnetic susceptibility.

Reversible unfolding of cytochrome c upon interaction with cardiolipin bilayers. 1. Evidence from deuterium NMR measurements

Deuterium NMR has been used to investigate the structure and dynamic state of cytochrome c complexed with bilayers of cardiolipin. Reductive methylation was employed to prepare [N epsilon, N epsilon-C2H3]lysyl cytochrome c, and deuterium exchange provided labeling of backbone sites to give [amide-2H]cytochrome c or more selective labeling of just histidine residues in [epsilon-2H]histidine cytochrome c. Deuterium NMR measurements on [N epsilon, N epsilon-C2H3]lysyl cytochrome c in the solid state showed restricted motions, fairly typical of the behavior of aliphatic side-chain sites in proteins. The [amide-2H]cytochrome c provided "immobile" amide spectra showing that only the most stable backbone sites remained labeled in this derivative. Relaxation measurements on the aqueous solution of [amide-2H]cytochrome c yielded a rotational correlation time of 7.9 ns for the protein, equivalent to a hydrodynamic diameter of 4.0 nm, just 0.6 nm greater than its largest crystallographic dimension. Similar measurements on [epsilon-2H]histidine cytochrome c in solution showed that all labeled histidine residues were also "immobile" compared with the overall reorientational motion of the protein. The interaction with cardiolipin bilayers appeared to create a high degree of mobility for the side-chain sites of [N epsilon, N epsilon-C2H3]lysyl cytochrome c and perturbed backbone structure to instantaneously release all deuterons in [amide-2H]cytochrome c. The [epsilon-2H]histidine cytochrome c derivative, when complexed with cardiolipin, failed to produce any detectable wide-line 2H NMR spectrum, demonstrating that the overall reorientational motion of bound protein was not isotropic on the NMR time scale, i.e., tau c greater than 10(-7)s.(ABSTRACT TRUNCATED AT 250 WORDS)

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--Part 22: ultraviolet radiation and photolysis

Parallels and similarities in chemical and functional damage to proteins by ionizing and UV radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Circular-dichroism studies of the cytochrome b-c1 complex of Saccharomyces cerevisiae

1. Circular dichroism studies on the Soret region of the cytochrome b-c1 complex of yeast reveal a change in the dichroism of cytochrome c1 depending on the redox state of cytochrome b, indicating a conformational interaction between both cytochromes. 2. This interaction is not influenced by binding of the inhibitor antimycin A to the complex, so that the interaction does not appear to be involved in the mechanism of electron transport through the complex. 3. Antimycin A binding causes a complex set of changes in the CD spectrum of the complex, which can be attributed to a severe and specific distortion of the environment of the chromophore of cytochrome b.

Solution behavior, circular dichroism and 22 HMz PMR studies of the bovine myelin basic protein

Bovine myelin basic protein has been investigated with regard to its solution behavior, circular dichroism and 220 MHz PMR spectral properties. At pH 4.8 gamma/2=0.1 acetate buffer, light scattering yielded a Mr of 17 700 and a virial coefficient of 1.0-10(-4) mol-ml/g2. Above pH 7.0 the protein was found to aggregate to higher mol. wt species. Sedimentation experiments at pH 4.8 yielded s degrees 20,w of 1.27 S at gamma/2=0.1 and 1.46 S at gamma/2=0.35. The diffusion coefficient determined from ultracentrifugal experiments was 7.25-10(-7) cm2/s at gamma/2=0.1 and 0.35. The value of f/f0 from diffusion at pH 4.8 and gamma/2=0.35 was 1.64, corresponding to an axial ratio of 11 to 1. The radius of gyration was calculated as 4.28 nm and the root mean square end to end distance was 10.5 nm. At pH 9.0, gamma/2=0.1, s degrees 20,w was 1.71 S and D degrees 20,w was estimated at 7.4-10(-7) cm2/s. The behavior at pH 9.0 reverted to the behavior at pH 4.8 when the pH was readjusted. The E1%/1cm=5.64 at 276.4 nm and 225 at 196 nm. Titration of the protein with trifluoroethanol elicited three distinct regions of conformation stability having increasing helical content as the mol fraction of trifluoroethanol increased. The results of the present study have permitted some comparison of analogous properties and conformational behavior with the basic membrane protein cytochrome c.