Lewy bodies, the pathological hallmark of dementia with Lewy bodies (DLB), are large juxtanuclear inclusions of aggregated ␣-synuclein. However, the small number of cortical Lewy bodies relative to the total neuron count does not correlate with the extent of cognitive impairment. In contrast to dopaminergic neurons in Parkinson's disease, nerve cell loss is usually less prevalent in the cortex of DLB, suggesting a different mechanism of neurodegeneration.Because antibodies used for immunodetection per se do not generally differentiate the aggregated from the physiological and monomeric isoform of ␣-synuclein, we developed the paraffin-embedded tissue (PET) blot and the protein aggregate filtration (PAF) assay for the sensitive and selective detection of ␣-synuclein aggregates in tissue slides and brain homogenates, respectively.In contrast to common immunohistochemistry, the PET blot detected an enormous number of small ␣-synuclein aggregates, which, in contrast to the few Lewy bodies, may explain the cognitive impairment in DLB. Using the PAF assay, we demonstrate that the absolute majority of ␣-synuclein aggregates are located at presynaptic terminals, suggesting a severe pathological impact on synaptic function. Indeed, parallel to the massive presynaptic accumulation of ␣-synuclein aggregates, we observed significant synaptic pathology with almost complete loss of dendritic spines at the postsynaptic area.Our results provide strong evidence for a novel concept of neurodegeneration for DLB in which synaptic dysfunction is caused by presynaptic accumulation of ␣-synuclein aggregates. This concept may also be valid for Parkinson's disease.

The prion protein is known to be a copper-binding protein, but affinity and stoichiometry data for the fulllength protein at a physiological pH of 7 were lacking. Furthermore, it was unknown whether only the highly flexible N-terminal segment with its octarepeat region is involved in copper binding or whether the structured C-terminal domain is also involved. Therefore we systematically investigated the stoichiometry and affinity of copper binding to full-length prion protein PrP 23-231 and to different N-and C-terminal fragments using electrospray ionization mass spectrometry and fluorescence spectroscopy. Our data indicate that the unstructured N-terminal segment is the cooperative copper-binding domain of the prion protein. The prion protein binds up to five copper(II) ions with half-maximal binding at ϳ2 M. This argues strongly for a direct role of the prion protein in copper metabolism, since it is almost saturated at about 5 M, and the exchangeable copper pool concentration in blood is about 8 M.

We present results on the identification and molecular characterization of conformers with secondary cis amide peptide bonds for a number of oligopeptides containing tyrosine and phenylalanine in aqueous solution. Employing 1 H NMR techniques, peptide bonds adjacent to the aromatic amino acid were found to generate a cis isomer population ranging from 0.1% to 1% in dependence on the chain length and the ionization state of the peptide. The rate constant of the trans f cis interconversion for zwitterionic Ala-Tyr was 2.4 × 10 -3 s -1 at 298 K and thus in a range typical of imidic prolyl peptide bonds. However, the rate constant k cis f trans ) 0.6 s -1 of the reverse isomerization revealed a much faster process in Ala-Tyr. Extending the peptide chain in both directions of the Ala-Tyr moiety led to a decrease of both the cis content and the barrier to rotation in the cis f trans direction. The linear Arrhenius plots gave E a values of 76.7 ( 1.5 and 64.6 ( 1.5 kJ mol -1 for the dipeptide Ala-Tyr and the corresponding bond in the pentapeptide Ala-Ala-Tyr-Ala-Ala, respectively. Isomerization rates were affected by both the position and the nature of amino acids flanking the isomerizing bond as could be proved by comparison of peptides containing Gly, Tyr, and Phe residues. These studies provide data that permit the extraction of kinetic events originating from the isomerization of "normal" peptide bonds in protein backbone structuring.

Direction finding of more sources than sensors is appealing in situations with small sensor arrays. Potential applications include surveillance, teleconferencing, and auditory scene analysis for hearing aids. A new technique for time-frequency-sparse sources, such as speech and vehicle sounds, uses a coherence test to identify low-rank time-frequency bins. These low-rank bins are processed in one of two ways: (1) narrowband spatial spectrum estimation at each bin followed by summation of directional spectra across time and frequency or (2) clustering low-rank covariance matrices, averaging covariance matrices within clusters, and narrowband spatial spectrum estimation of each cluster. Experimental results with omnidirectional microphones and colocated directional microphones demonstrate the algorithm's ability to localize 3-5 simultaneous speech sources over 4 s with 2-3 microphones to less than 1 degree of error, and the ability to localize simultaneously two moving military vehicles and small arms gunfire.