An amyloid(1-40) solution rich in coil, turn, and alpha-helix, but poor in beta-sheet, develops monolayers with a high beta-sheet content when spread at the air-water interface. These monolayers are resistant to repeated compression-dilatation cycles and interaction with trifluoroethanol. The secondary structure motifs were detected by circular dichroism (CD) in solution and with infrared reflection-absorption spectroscopy (IRRAS) at the interface. Hydrophobic influences are discussed for the structure conversion in an effort to understand the completely unknown reason for the natural change of the normal prion protein cellular (PrP(C)) into the abnormal prion protein scrapie (PrP(Sc)).

No abstract

In order to study the conformational behavior of poly(L-glutamic acid) (PGA) at the air/water interface under the influence of compression and expansion forces, PGA was spread on an aqueous acidic subphase and studied by the Langmuir technique. Several distinct regions of the first compression surface pressure/ area (π/A) isotherm could be identified by the starting and inflection point of the isotherm and by the beginning and the center of the pseudoplateau. The interpretation of the characteristic shape of the π/A isotherms in the sense of a side-by-side and an interdigitated organization of helical rods is strongly supported by molecular modeling calculations. But the helical surface layer is sensitive to repeated expansion and compression. A well-defined and reaction-kinetic demonstrable change occurs. The reasons for this transformation are discussed. Solidified regions are forming in the layer. Finally, after several compression/ expansion cycles a more rigid monolayer results than that formed by helical rods exclusively. These monolayer ruptures on expansion and clods of PGA molecules were observed using Brewster angle microscopy and ellipsometry.

The modification of the triple helical structure in aqueous gelatin solutions by changing pH and adding alkyl sulphates at 298 K and after rechilling the solution to 283 K was investigated by CD-measurement. At 298 K the triple helical content at the IEP of the gelatin has its maximum value. It is only weakly affected by adding sodium dodecyl sulphate (SDDS) at concentrations < 10 -4 M/dm 3. The unfolding of the triple helix affected by pH and SDDS is reversible by rechilling the solution. The triple helical content of gelatin solutions decreases at SDDS concentrations higher than 10 -4 M/dm 3. In all cases the decrease of the amount of triple helical structure is connected with an increase of the cis-configuration in single chains and leads to chain reversals. At sufficiently high SDDS concentrations 3-sheets are formed. These changes are thermally irreversible. Sodium decyl sulphate (SDS) has a more minor influence than SDDS except in the range of the c.m.c, of SDS. At sufficiently high SDS concentrations, 3-turns appear.