From protons to OXPHOS supercomplexes and Alzheimer's disease: Structure–dynamics–function relationships of energy-transducing membranes

AbstractBy the elucidation of high-resolution structures the view of the bioenergetic processes has become more precise. But in the face of these fundamental advances, many problems are still unresolved. We have examined a variety of aspects of energy-transducing membranes from large protein complexes down to the level of protons and functional relevant picosecond protein dynamics. Based on the central role of the ATP synthase for supplying the biological fuel ATP, one main emphasis was put on this protein complex from both chloroplast and mitochondria. In particular the stoichiometry of protons required for the synthesis of one ATP molecule and the supramolecular organisation of ATP synthases were examined. Since formation of supercomplexes also concerns other complexes of the respiratory chain, our work was directed to unravel this kind of organisation, e.g. of the OXPHOS supercomplex I1III2IV1, in terms of structure and function. Not only the large protein complexes or supercomplexes work as key players for biological energy conversion, but also small components as quinones which facilitate the transfer of electrons and protons. Therefore, their location in the membrane profile was determined by neutron diffraction. Physico-chemical features of the path of protons from the generators of the electrochemical gradient to the ATP synthase, as well as of their interaction with the membrane surface, could be elucidated by time-resolved absorption spectroscopy in combination with optical pH indicators. Diseases such as Alzheimer's dementia (AD) are triggered by perturbation of membranes and bioenergetics as demonstrated by our neutron scattering studies

Cholesterol inhibits the insertion of the Alzheimer s peptide A 2 25 35 in lipid bilayers

Abstract The physiological relationship between brain cholesterol content and the action of amyloid beta Abeta peptide in Alzheimer s disease AD is a highly controversially discussed topic. Evidences for modulations of the A? membrane interaction induced by plasma membrane cholesterol have been already observed. We have recently reported that Abeta 25 35 is capable to insert in lipid membranes and to perturb their structure. Applying neutron diffraction and selective deuteration, we demonstrate now that cholesterol alters at the molecular level the capability of Abeta 25 35 to penetrate into the lipid bilayers; in particular, a molar weight content of 20 of cholesterol hinders completely the intercalation of monomeric Abeta 25 35 . At very low cholesterol content about 1 molar weight the location of the C terminal part of Abeta 25 35 has been unequivocally established in the hydrocarbon region of the membrane, in agreement with our previous results on pure phospholipids membrane. These results link a structural property to a physiological and functional behavior, and point to a therapeutical approach to prevent the AD by modulation of membrane properties

Influence of amyloid beta peptides with different lengths and amino acid sequences on the lateral diffusion of lipids in model membranes

We have investigated the influence of two neurotoxic Alzheimer s disease peptide analogues with different lengths and amino acid compositions, amyloid b 25 35 and amyloid b 22 40 , on the dynamics of phospholipid membranes by means of quasi elastic neutron scattering in the picosecond time domain. Samples of pure phospholipids DMPC DMPS and samples with embedded amyloid b peptides have been compared. The peptide concentration was 3 mol for both amyloid b peptides. The sample temperature was set to 320 K, where the samples are in the liquid crystalline phase, which is the physiologically relevant phase of biological membranes. The data have been analyzed with a purely phenomenological model, which combines two different motions with different time constants. These two motions have been assigned to a long range translational diffusion and a spatially restricted localized diffusion. The different lengths of the peptides leads to different positions and orientations inside the membrane bilayers. Thus, different influences on the dynamics are also expected. Both amyloid b peptides significantly affected the ps dynamics of oriented lipid membranes. Mainly, they accelerated the long range translational diffusion even though the peptide concentration was quite low. This finding is of relevance for all kinds of protein protein interactions, which are strongly influenced by the lateral diffusion, such as signal transduction cascades and energy transfer. This influence might be involved in the pathology of Alzheimer s disease as well as being therapy

Beta amyloid 25 to 35 is intercalated in anionic and zwitterionic lipid membranes to different extents

Neuronal plasma membranes are thought to be the primary target of the neurotoxic beta-amyloid peptides (Abeta) in the pathogenesis of the Alzheimer's disease. Histologically, Abeta peptides are observed as extracellular macroscopic senile plaques, and most biophysical techniques have indicated the presence of Abeta close to the lipid headgroup region but not in the core of the membrane bilayers. The focus of this study is an investigation of the interaction between Abeta and lipid bilayers from a structural point of view. Neutron diffraction with the use of selectively deuterated amino acids has allowed us to determine unambiguously the position of the neurotoxic fragment Abeta (25-35) in the membrane. Two populations of the peptide are detected, one in the aqueous vicinity of the membrane surface and the second inside the hydrophobic core of the lipid membrane. The location of the C terminus was studied in two different lipid compositions and was found to be dependent on the surface charge of the membrane. The localization of beta-amyloid peptides in cell membranes will offer new insights on their mechanism in the neurodegenerative process associated with Alzheimer's disease and might provide clues for therapeutic developments

Relationship between structure, dynamics and function of hydrated purple membrane investigated by neutron scattering and dielectric spectroscopy

We investigated the influence of hydration water on the relationship between structure, dynamics and function in a biological membrane system. For the example of the purple membrane PM with its protein bacteriorhodopsin BR , a light driven proton pump, complementary information from neutron diffraction, quasi elastic neutron scattering QENS and dielectric spectroscopy will form a comprehensive picture of the structural and dynamic behavior of the PM in the temperature range between 150 and 290 K. Temperature and humidity dependent changes in the membrane system influence the accessibility of the different photocycle intermediates of BR. The melting of the freezing bound water between 220 and 250 K could be related to the transition from the M1 to the M2 intermediate, which represents the key step in the photocycle. The dynamic transition in the vicinity of 180 K was shown to be necessary to ensure that the M1 intermediate can be populated and that the melting of crystallized bulk water above 255 K enables the completion of the photocycl

Membrane fusogenic activity of the Alzheimer s peptide A 1 42 demonstrated by small angle neutron scattering

Amyloid ? peptide A? is considered a triggering agent of the Alzheimer s disease AD . To understand its mechanism of action and in relationship to a therapeutic treatment of the disease, the interaction of A? with the cell membrane has to be elucidated at the molecular level. In previous works 1 3 we had ascertained by neutron diffraction on stacked lipid multilayers that a toxic fragment of A? is able to penetrate and perturb the lipid bilayer. Here the influence of A? 1 42 , the most abundant A? form in senile plaques, on unilamellar vesicles ULV of phospholipids is investigated by small angle neutron scattering SANS . We have used the recently proposed separated form factor SFF method to fit the data and to obtain information about the structure of the lipid bilayer and its change upon peptide administration. The lipid membrane parameters were obtained with different models of the bilayer profile. As a result, we obtained an increase of the vesicle radii indicating vesicle fusion. This effect was particularly enhanced at pH 7.0 and at a high peptide lipid ratio. At the same time, a thinning of the lipid bilayer occurred. A fusogenic activity of the peptide may have very important consequences and contribute to cytotoxicity by destabilizing the cell membrane. The perturbation of the bilayer structure suggests a strong interaction and or insertion of the peptide into the membrane, although its localization remains beyond the limit of the experimental resolutio