No abstract

The basic fraction of a 2-aminopropionitrile polymer was subjected to acid hydrolysis and was analyzed by means of GC-MS, after trimethylsilylation. The fundamental polymer structural units were alanine, 2,2'-iminodipropionic acid, N-(1-cyanoethyl)alanine, N-ethylalanine, glycine, cyanoglycine, and 5-amino-4-carboxyimidazole residues. The last three units may be derived from hydrogen cyanide. Oligomeric combinations of these units were also detected in the hydrolyzate, due to partial hydrolysis of the polymer.

Recent evidence suggests that soluble amyloid-b (Ab) oligomers as small as dimers may be linked to the progression of Alzheimer's disease. We have used single-pair FRET measurements to investigate heterogeneity in surfacetethered dimers of Ab40, probing for preferred structures. Dimers are prepared by combining monomers singly labeled with donor and acceptor dyes; dimers prepared in solution (prior to surface-tethering) and on the functionalized surface have been examined. Donor and acceptor fluorescence are separated onto two detectors, such that co-localized spots in two-color images are indicative of at least two associated peptides. Dimers are verified based on the observation of single-step photobleaching in each detection channel; larger oligomers are excluded from analysis. By measuring donor and acceptor fluorescence as a function of time, we have determined time-dependent FRET efficiencies for dozens of individual dimers, permitting insight into inter-dye distances and dimer structures. These results are further complemented by comparison to published structures of simulated Ab40 dimers. Together, experiment and simulation may reveal a subset of preferred structures for Ab40 dimers.

accuracy in distance measurements between two different color dye-molecules attached at known positions along a surface tethered bio-molecule. The statistical uncertainty in the mean for an ensemble of N~10 identical single molecule samples is limited only by the total number of collected photons to ~0.3nm, or ~0.002 of the width of the optical PSF. We further show how our method can be used to improve the resolution of many sub-wavelength, far-field imaging methods such as those based on co-localization of stochastically excited fluorescent molecules. Conclusion: We demonstrate sub-nanometer resolution in measurements of molecular-scale distances using far-field fluorescence imaging optics, at room temperature and in physiological buffer conditions. The improved resolution will allow deciphering in real-time, at the single molecule level the structure and dynamics of large, multi-subunit biological complexes.