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

The effectiveness of two silicone dressings for sacral and heel pressure ulcer prevention compared with no dressings in high‐risk intensive care unit patients: a randomized controlled parallel‐group trial

Background There is a high incidence of pressure ulcers in high-risk settings such as intensive care. There is emerging evidence that the application of dressings to pressure ulcer predilection areas (sacrum and heels) improves prevention strategies. Objectives To determine whether preventive dressings, applied to the sacrum and heels of high-risk patients in intensive care units, in addition to standard prevention, reduces the incidence of pressure ulcers. Methods Between June 2015 and July 2018, a randomized, controlled, two-arm, superiority pragmatic study was performed with a concealed 1 : 1 allocation to the intervention and control group. Patients assigned to the intervention group had dressings applied to the sacrum and heels. Results In total, 7575 patients were screened for eligibility and 475 patients were included and allocated to both groups. Finally, 212 patients in the intervention group and 210 in the control group were analysed. The mean age was 63 center dot 5 years and the majority of patients were male (65 center dot 4%). The cumulative pressure ulcer incidence category II and above was 2 center dot 8% in the intervention, and 10 center dot 5% in the control group (P = 0 center dot 001). Compared with the control group, the relative risk in the intervention group was 0 center dot 26 [95% confidence interval (CI) 0 center dot 11-0 center dot 62] and the absolute risk reduction was 0 center dot 08 (95% CI 0 center dot 03-0 center dot 13). Conclusions The results indicate that the application of dressings, in addition to standard prevention, in high-risk intensive care unit patients is effective in preventing pressure ulcers at the heels and sacrum. What's already known about this topic? Pressure ulcers are severe soft tissue injuries and wounds, which occur worldwide in all healthcare settings. Despite preventive interventions, pressure ulcers still develop. There is emerging evidence that dressings help to prevent pressure ulcers. What does this study add? The incidence of pressure ulcers in intensive care units among high-risk patients remains high. The application of dressings to the sacrum and heels, in addition to standard preventive measures, reduces the relative and absolute risks for the development of pressure ulcers. The application of preventive dressings at the heels and sacrum seems to be feasible in intensive care settings

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

Biophysical investigation into the antibacterial action of modelin-5-NH2

Modelin-5-CONH2 (M5-NH2) is a synthetic antimicrobial peptide, which was found to show potent activity against Bacillus subtilis (Minimum lethal concentration = 8.47 µM) and to bind strongly to membranes of the organism (Kd = 10.44 µM). The peptide adopted high levels of amphiphilic α-helical structure in the presence of these membranes (> 50 %), which led to high levels of insertion (Δπ ≥ 8.0 mN m-1). M5-NH2 showed high affinity for anionic lipid (Kd = 7.46 µM) and zwitterionic lipid (Kd = 14.7 µM), which drove insertion into membranes formed from these lipids (Δπ = 11.5 and 3.5 mN m-1, respectively). Neutron diffraction studies showed that M5-NH2 inserted into B. subtilis membranes with its N-terminal residue, L16, located 5.5 Å from the membrane centre, in the acyl chain region of these membranes, and promoted a reduction in membrane thickness of circa 1.8 Å or 5 % of membrane width. Insertion into B. subtilis membranes by the peptide also promoted other effects associated with membrane thinning, including increases in membrane surface area (Cs-1 decreases) and fluidity (ΔGmix > 0 to ΔGmix 55%), and it is speculated that the antibacterial action of the peptide may involve the toroidal pore, carpet or tilted-type mechanism of membrane permeabilization

Localization of coenzyme Q10 in the center of a deuterated lipid membrane by neutron diffraction

AbstractQuinones (e.g., coenzyme Q, CoQ10) are best known as carriers of electrons and protons during oxidative phosphorylation and photosynthesis. A myriad of mostly more indirect physical methods, including fluorescence spectroscopy, electron-spin resonance, and nuclear magnetic resonance, has been used to localize CoQ10 within lipid membranes. They have yielded equivocal and sometimes contradictory results. Seeking unambiguous evidence for the localization of ubiquinone within lipid bilayers, we have employed neutron diffraction. CoQ10 was incorporated into stacked bilayers of perdeuterated dimyristoyl phosphatidyl choline doped with dimyristoyl phosphatidyl serine containing perdeuterated chains in the natural fluid-crystalline state. Our data show CoQ10 at the center of the hydrophobic core parallel to the membrane plane and not, as might be expected, parallel to the lipid chains. This localization is of importance for its function as a redox shuttle between the respiratory complexes and, taken together with our recent result that squalane is in the bilayer center, may be interpreted to show that all natural polyisoprene chains lie in the bilayer center. Thus ubiquinone, in addition to its free radical scavenging and its well-known role in oxidative phosphorylation as a carrier of electrons and protons, might also act as an inhibitor of transmembrane proton leaks

Dynamics in biological membranes from neutron scattering and dielectric spectroscopy experiments

We report dielectric spectroscopy DS results from temperature T and hydration h dependent measurements on multi layer stacks of purple membrane PM . The frequency dependent dielectric permittivity conveys dynamic information, since it images electric dipole motions. In the investigated range of the physical parameters 235 K lt; T lt; 275 K, 0.23 wt H2O lt; h lt; 0.47 wt H2O, 10 3 amp; 8804; f amp; 8804; 10 6 Hz , the dielectric permittivity of PM stacks, their lamellar lattice constant and the quasielastic incoherent structure factors QISFs exhibit a qualitatively very similar behavior as a function of T and h. A supercooling effect with a freezing discontinuity at the temperature Tfh and a continuous increase of the dielectric permittivity upon reheating, with a melting discontinuity point Tmh gt; Tfh, were observed. The variation of Tmh as a function of water content resembles very much the neutron result, except for a systematic difference due to the use of H2O for DS rather than D2O for neutrons as solvent. The existence of crystalline ice at temperatures below 245 K, known from neutron diffraction, has now been demonstrated by dielectric spectroscopy as well. The imaginary part of the frequency dependent dielectric function exhibits two relaxation peaks at low temperature e.g., f 800 Hz and 25000 Hz, at 223 K , while at higher temperatures the dielectric spectrum is conductivity dominated, showing no relaxation peaks. All in all, we demonstrate the extremely useful complementarity of dielectric spectroscopy and neutron scattering, both working in different frequency regime