Squalane is in the midplane of the lipid bilayer: implications for its function as a proton permeability barrier

AbstractA recently proposed model for proton leakage across biological membranes [Prog. Lipid Res. 40 (2001) 299] suggested that hydrocarbons specifically in the center of the lipid bilayer inhibit proton leaks. Since cellular membranes maintain a proton electrochemical gradient as a principal energy transducer, proton leakage unproductively consumes cellular energy. Hydrocarbons in the bilayer are widespread in membranes that sustain such gradients. The alkaliphiles are unique in that they contain up to 40 mol% isoprenes in their membranes including 10–11 mol% squalene [J. Bacteriol. 168 (1986) 334]. Squalene is a polyisoprene hydrocarbon without polar groups. Localizing hydrocarbons in lipid bilayers has not been trivial. A myriad of physical methods including fluorescence spectroscopy, electron-spin resonance, nuclear magnetic resonance as well as X-ray and neutron diffraction have been used to explore this question with various degrees of success and often contradictory results. Seeking unambiguous evidence for the localization of squalene in membranes or lipid bilayers, we employed neutron diffraction. We incorporated 10 mol% perdeuterated or protonated squalane, an isosteric analogue of squalene, into stacked bilayers of dioleoyl phosphatidyl choline (DOPC) doped with dioleoyl phosphatidyl glycerol (DOPG) to simulate the negative charges found on natural membranes. The neutron diffraction data clearly show that the squalane lies predominantly in the bilayer center, parallel to the plane of the membrane

Role of Mitochondrial Protein Import in Age-Related Neurodegenerative and Cardiovascular Diseases

Mitochondria play a critical role in providing energy, maintaining cellular metabolism, and regulating cell survival and death. To carry out these crucial functions, mitochondria employ more than 1500 proteins, distributed between two membranes and two aqueous compartments. An extensive network of dedicated proteins is engaged in importing and sorting these nuclear-encoded proteins into their designated mitochondrial compartments. Defects in this fundamental system are related to a variety of pathologies, particularly engaging the most energy-demanding tissues. In this review, we summarize the state-of-the-art knowledge about the mitochondrial protein import machinery and describe the known interrelation of its failure with age-related neurodegenerative and cardiovascular diseases

Nachweis eines Retinal-Protein-Komplexes als wirksames Pigment der direkten photophobischen Reaktion (PS 370) von Halobacterium halobium, sowie spektroskopische und biochemische Untersuchungen am Bacteriorhodopsin der Purpurmembran

Both photosystems, PS 370 and PS 565, controlling behavioral responses in Halobacteriurn halobiurn are reversibly inhibited when bacteria are grown in the presence of 1 mM nicotine which is known to block biosynthesis of retinal. Photobehavior can be restored within some minutes to hours' by adding retinal to nicotine-treated bacteria, PS 370 thereby reappearing earlier than PS 565. The reconstitution rate depends on the concentration and on the kind of retinal isomers applied. All-trans retinal is most effective. PS 370 becomes fully sensitive if reconstituted in the presence of nicotine. This rules out the possibility that the alkaloid may directly inhibit steps of signal transmission following photoreception. The action spectrurn of PS 370 regenerated with retinal alone of H.h., strain R$_{1}$L$_{3}$ (a mutant deficient in carotenoids), fails to show all secondary peaks around 450 nm which in strain R$_{1}$ occur besides the prominent maximum at 370 nm. Addition of carotenoids (mainly a-bacterioruberin) to reconstituted cells of R$_{1}$L$_{3}$ restores the sensitivity in that spectral region. Carotenoids or flavin solely added to nicotine-treated baeteria cannot res tore photobehavior. These results indicate that the active pigment of PS 370, which mediates the photophobie response to increase of light intensity (step-up response), represents a retinal protein complex and that carotenoids partieipate in photoreeeptor function as accessory pigments. The biochemical relation of the UV-absorbing retinal protein complex to bacteriorhodopsin is discussed

Monomeric and aggregated bacteriorhodopsin: Single-turnover proton transport stoichiometry and photochemistry

The question of the basic functional transport unit of bacteriorhodopsin (BR) has been addressed by comparing the proton pumping stoichiometry as well as the photocycle kinetics of monomeric and aggregated BR in phospholipid vesicles. When time-resolved laser spectroscopy was used in combination with the optical pH-indicator pyranine, single-turnover experiments revealed approximately 0.5-0.8 and 0.8-1.2 protons vectorially translocated per photocycling monomeric and aggregated BR molecule, respectively. Since both these values are akin and very similar to the pumping stoichiometry of crystalline BR molecules in the purple membrane, the BR monomer has been proven to be the essential transport unit. The natural arrangement of the photopigments in a crystalline array of immobilized trimers is not required for efficient vectorial proton translocation

Oxygen Concentration and Oxidative Stress Modulate the Influence of Alzheimer’s Disease Aβ1–42 Peptide on Human Cells

Reactive oxygen species (ROS) generated after exposure to ionizing radiation and toxic peptides, in mitochondrial metabolism and during aging contribute to damage of cell’s structural and functional components and can lead to diseases. Monomers and small oligomers of amyloid beta (Aβ) peptide, players in Alzheimer’s disease, are recently suggested to be involved in damaging of neurons, instead of extracellular Aβ plaques. We demonstrate that externally applied disaggregated Aβ1–42 peptide interacts preferentially with acidic compartments (lysosomes). We compared standard cell cultivation (21% O2) to more physiological cell cultivation (5% O2). Cells did not exhibit a dramatic increase in ROS and change in glutathione level upon 4 μM Aβ peptide treatment, whereas exposure to 2 Gy X-rays increased ROS and changed glutathione level and ATP concentration. The occurrence of the 4977 bp deletion in mtDNA and significant protein carbonylation were specific effects of IR and more pronounced at 21% O2. An increase in cell death after Aβ peptide treatment or irradiation was unexpectedly restored to the control level or below when both were combined, particularly at 5% O2. Therefore, Aβ peptide at low concentration can trigger neuroprotective mechanisms in cells exposed to radiation. Oxygen concentration is an important modulator of cellular responses to stress