Schwingungsspektroskopische Analysen der Sekundärstruktur von Peptiden

The "$\beta$-peptide" (103), a synthetic tridecapeptide, was designed to form an antiparallel $\beta$-sheet containing a turn to connect both strands. By infrared- and Fourier Transform infrared spectroscopy, the peptide was confirmed to be mainly of the depicted conformation. This structure was shown to exist in both, KBr-pellets and aqueous solution. Dispersive infrared measurements have shown that a second peptide, "Con A 1/4" (92), is an antiparallel $\beta$-sheet without a turn. In contrast to the $\beta$-Wpeptide, the structure of Con A 1/4 is based on the antiparallel alignment of several molecules. A detailed model for this aggregation has been proposed. Structure analysis of cystein-containing peptides, being modelled on the active site of the basic pancreatic trypsin inhibitor (41) was confirmed indirectly by combination of several vibration spectroscopic methods: - Normal Raman spectroscopy was used to determine the conformation of disulfide-bridges in oxidized peptide III, like the lack of disulfide-bridges in reduced peptide II. - Dispersive infrared-spectroscopy showed a mainly similar secondary structure of the peptides II andIII in their oxidized and reduced forms. - Surface enhanced Raman spectroscopy (SERS) revealed a likewise distribution of amino acids on the surfaceof peptide II and III. In summary, it has to be concluded that both peptides in their oxidized as well as in their reduced form are very rigid antiparallel $\beta$-sheets flanking a tight $\beta$-turn. According to Fourier Transform infrared measurements the secondary structure of reduced peptide II is mainly identical in aqueous solution and pressed KBr. Both, SERS-experiments and dispersive infrared measurements proved for peptide I a structure being quite different from peptides II and III. The secondary structures of several peptides, synthesized to examine the structure of the protein fibrillary deposits found in Alzheimer's disease, were determined by dispersive infrared spectroscopy and compared with the secondary structure of °native" deposits (amyloide plaque cores (APC)). In connection with these experiments, the secondary structure of different peptide aggregates have been examined with regard to temperature stability. Concluding from these spectroscopic results, in agreement with biochemical experiments (68, 74, 88, pers. comm. K. Beyreuther, C. Hilbich, U. Mönning) and data from x-ray analysis (51) models were developed to account for the secondary structures of different synthetic peptides as well as for the structure and aggregation of fibrillary deposits in the brain. Starting from these models, it might be possible to explain the differing morphology of both types of native filaments (APC and paired helical filaments (PHF)) as well as the morphology of fibrils created by coaggregation of two peptides (1-28 and 4-28)