Modelling Ser129 Phosphorylation Inhibits Membrane Binding of Pore-Forming Alpha-Synuclein Oligomers

Background: In several neurodegenerative diseases, hyperphosphorylation at position Ser129 is found in fibrillar deposits of alpha-synuclein (asyn), implying a pathophysiological role of asyn phosphorylation in neurodegeneration. However, recent animal models applying asyn phosphorylation mimics demonstrated a protective effect of phosphorylation. Since metal-ion induced asyn oligomers were identified as a potential neurotoxic aggregate species with membrane pore-forming abilities, the current study was undertaken to determine effects of asyn phosphorylation on oligomer membrane binding. Methods: We investigated the influence of S129 phosphorylation on interactions of metal-ion induced asyn oligomers with small unilamellar lipid vesicles (SUV) composed of POPC and DPPC applying the phosphorylation mimic asyn129E. Confocal single-particle fluorescence techniques were used to monitor membrane binding at the single-particle level. Results: Binding of asyn129E monomers to gel-state membranes (DPPC-SUV) is slightly reduced compared to wild-type asyn, while no interactions with membranes in the liquid-crystalline state (POPC-SUV) are seen for both asyn and asyn129E. Conversely, metal-ion induced oligomer formation is markedly increased in asyn129E. Surprisingly, membrane binding to POPC-SUV is nearly absent in Fe3+ induced asyn129E oligomers and markedly reduced in Al3+ induced oligomers. Conclusion: The protective effect of pseudophosphorylation seen in animal models may be due to impeded oligomer membrane binding. Phosphorylation at Ser129 may thus have a protective effect against neurotoxic asyn oligomers by preventing oligomer membrane binding and disruption of the cellular electrophysiological equilibrium. Importantly, these findings put a new complexion on experimental pharmaceutical interventions against POLO-2 kinase

Time-bin entangled photon pairs from Bragg-reflection waveguides

This work was supported by the Austrian Science Fund (FWF) through the project nos. I 2065 and J 4125, the DFG project no. SCHN1376/2-1, the ERC project EnSeNa (257531), the State of Bavaria and China Scholarship Council (201503170272).Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state’s density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of 88.9(1.8)% and a fidelity of 94.2(9)% with respect to a Bell state.Publisher PDFPeer reviewe

Highly anisotropic decay rates of single quantum dots in photonic crystal membranes

We have measured the variation of the spontaneous emission rate with polarization for self-assembled single quantum dots in two-dimensional photonic crystal membranes. We observe a maximum anisotropy factor of 6 between the decay rates of the two bright exciton states. This large anisotropy is attributed to the substantially different projected local density of optical states for differently oriented dipoles in the photonic crystal. (C) 2010 Optical Society of America</p

Integrated semiconductor quantum photonics

For fundamental tests of quantum physics as well as for quantum communications, non-classical states of light are an important tool. In this talk, we will present our work on developing nonlinear AlGaAs waveguides into a platform for quantum photonics in semiconductors. Most III-V semiconductors exhibit a large second-order optical nonlinearity, but phase-matching the nonlinear interaction is notoriously difficult. As a solution Bragg-reflection waveguides allow efficient creation of photon pairs through spontaneous parametric down-conversion. They have the potential to be homogeneously integrated with a pump laser and passive and active components on the chip.</p

Pulsed Nuclear Pumping and Spin Diffusion in a Single Charged Quantum Dot

We report the observation of a feedback process between the nuclear spins in a single charged quantum dot and its trion transition, driven by a periodic sequence of optical pulses. The pulse sequence intersperses off-resonant ultrafast pulses for coherent electron-spin rotation and resonant narrow-band optical pumping. The feedback manifests as a hysteretic triangle-like pattern in the free-induction-decay of the single spin. We present a simple, quasi-analytic numerical model to describe this observation, indicating that the feedback process results from the countering effects of optical nuclear pumping and nuclear spin-diffusion inside the quantum dot. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.Comment: 4 pages, 3 figure

Integrated semiconductor quantum photonics

For fundamental tests of quantum physics as well as for quantum communications, non-classical states of light are an important tool. In this talk, we will present our work on developing nonlinear AlGaAs waveguides into a platform for quantum photonics in semiconductors. Most III-V semiconductors exhibit a large second-order optical nonlinearity, but phase-matching the nonlinear interaction is notoriously difficult. As a solution Bragg-reflection waveguides allow efficient creation of photon pairs through spontaneous parametric down-conversion. They have the potential to be homogeneously integrated with a pump laser and passive and active components on the chip.</p