1-palmitoyl-2-oleoylglycero-3-phosphoserine and 1-2-dioleoylphosphatidylserine

The neuronal protein α-synuclein, linked to Parkinson's disease, binds to negatively charged vesicles adopting a partial α-helix structure, but helix arrangement at the vesicle surface is not fully understood. Using linear dichroism spectroscopy (LD), we study the interaction of monomeric α-synuclein with large unilamellar vesicles of 1,2-dioleoyl-

Topics: alpha-Synuclein; Amino Acid Sequence; Phosphatidylglycerols; Phosphatidylserines; Protein Binding; Protein Conformation, alpha-Helical; Unilamellar Liposomes

α-Synuclein (α-Syn) is an abundant cytosolic protein involved in the release of neurotransmitters in presynaptic terminal and its aberrant aggregation is found to be associated with Parkinson's disease. Recent study suggests that the oligomers formed at the initial oligomerization stage may be the root cause of cytotoxicity. While characterizing this stage is challenging due to the inherent difficulties in studying heterogeneous and transient systems by conventional biochemical technology. Here we use solid-state nanopores to study the time-dependent kinetics of α-Syn oligomerization through a label-free and single molecule approach. A tween 20 coating method is developed to inhibit non-specific adsorption between α-Syn and nanopore surface to ensure successful and continuous detection of α-Syn translocation. We identify four types of oligomers formed in oligomerization stage and find an underlying consumption mechanism that the formation of large oligomers consumes small oligomers. Furthermore, the effect of lipid membrane on oligomerization of α-Syn is also investigated and the results show that 1,2-dioleoyl-sn-glycero-3-[phospho-L-serine] (DOPS) small unilamellar vesicles (SUVs) dramatically enhances the aggregation rate of α-Syn while do not alter the aggregation pathway.

Topics: alpha-Synuclein; Amino Acid Sequence; Humans; Nanopores; Phosphatidylserines; Polysorbates; Protein Aggregates; Protein Multimerization; Protein Transport; Surface Properties; Unilamellar Liposomes

The isothermal phase behavior of three gramicidin A'/phospholipid mixtures was investigated by an equilibrium Ca(2+)-binding technique. The phospholipid component was 1,2-dioleoyl-sn-glycero-3-phosphoserine (DOPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS), or POPS/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at a constant mole ratio of 1/4. The bulk aqueous free Ca2+ concentration, [Ca2+]*f, in equilibrium with one or two gramicidin A'/phospholipid fluid phases and a small amount of the Ca (phosphatidylserine)2 gel phase, was measured as a function of composition at 20 degrees C by use of chromophoric high-affinity Ca2+ chelators. The coexistence of two gramicidin A'/phospholipid fluid phases was detected by an invariance in [Ca2+]*f over the range of compositions throughout which the two phases coexist. The compositions of the two coexisting phases are determined by the compositions at which the invariance in [Ca2+]*f begins and ends. With each of the gramicidin A'/phospholipid mixtures, we estimate that the composition of the gramicidin-poor phase is 0.03-0.04 mole fraction gramicidin A' and the composition of the gramicidin-rich phase is 0.13-0.14 mole fraction gramicidin A'. Characterization of these phases by low-angle X-ray diffraction revealed that, in each case, the gramicidin-poor phase is an L alpha phase and the gramicidin-rich phase is an HII phase. The isothermal phase behavior of gramicidin A'/POPC mixtures at approximately 23 degrees C, as determined by low-angle X-ray diffraction, was found to be similar to that of the other gramicidin A'/phospholipid mixtures.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Binding Sites; Calcium; Chelating Agents; Gramicidin; Kinetics; Magnetic Resonance Spectroscopy; Phosphatidylcholines; Phosphatidylserines; Phosphorus Radioisotopes; Reference Standards; X-Ray Diffraction

Ca2+ binding between phosphatidylserine (PS) lamellae gives rise to a phase with the composition Ca(PS)2. When aqueous Ca2+, hydrated PS, and Ca(PS)2 coexist at equilibrium, the aqueous Ca2+ concentration is invariant. At Ca2+ concentrations below this critical value, no binding of Ca2+ to PS is detected. Above this value, Ca2+ binds to PS to form Ca(PS)2. The invariant Ca2+ concentration is 0.14 microM for palmitoyloleoylphosphatidylserine (POPS) and 3.0 microM for dioleoylphosphatidylserine (DOPS). For the mixed acyl chain PS derived from bovine brain (BBPS) this Ca2+ concentration ranges from 0.25 to 0.7 microM. The observed phase behavior is described by the phase rule for the three-component system of water, Ca2+, and PS, with temperature and pressure constant. In order for Ca2+ to bind between PS lamellae to form the Ca(PS)2 phase, the aqueous Ca2+ concentration must be supersaturated. The equilibrium Ca2+ concentration is determined by dissolving Ca(PS)2 by use of Ca2+ chelators.

Topics: Animals; Brain; Calcium; Cations; Cattle; Chemical Phenomena; Chemistry; Phosphatidylserines; Solutions; Structure-Activity Relationship