Alignment of a Model Amyloid Peptide Fragment in Bulk and at a Solid Surface

Abstract

The alignment of model amyloid peptide YYKLVFFC is investigated in bulk and at a solid surface using a range of spectroscopic methods employing polarized radiation. The peptide is based on a core sequence of the amyloid beta (Abeta) peptide, KLVFF. The attached tyrosine and cysteine units are exploited to yield information on alignment and possible formation of disulfide or dityrosine links. Polarized Raman spectroscopy on aligned stalks provides information on tyrosine orientation, which complements data from linear dichroism (LD) on aqueous solutions subjected to shear in a Couette cell. LD provides a detailed picture of alignment of peptide strands and aromatic residues and was also used to probe the kinetics of self-assembly. This suggests initial association of phenylalanine residues, followed by subsequent registry of strands and orientation of tyrosine residues. X-ray diffraction (XRD) data from aligned stalks is used to extract orientational order parameters from the 0.48 nm reflection in the cross-beta pattern, from which an orientational distribution function is obtained. X-ray diffraction on solutions subject to capillary flow confirmed orientation in situ at the level of the cross-beta pattern. The information on fibril and tyrosine orientation from polarized Raman spectroscopy is compared with results from NEXAFS experiments on samples prepared as films on silicon. This indicates fibrils are aligned parallel to the surface, with phenyl ring normals perpendicular to the surface. Possible disulfide bridging leading to peptide dimer formation was excluded by Raman spectroscopy, whereas dityrosine formation was probed by fluorescence experiments and was found not to occur except under alkaline conditions. Congo red binding was found not to influence the cross-beta XRD pattern.

A Thermoresponsive Hydrogel Based on Telechelic PEG End‐Capped with Hydrophobic Dipeptides

“…The minimum at 259 nm is associated with the tyrosine residues. [23,26] Consistent with the FTIR data, a CD spectrum measured for conjugate 4 showed no b-sheet features (Figure 2a), instead there is a minimum at 207 nm and a maximum at 217 nm. These features are associated with contributions from phenylalanine residues.…”

“…The latter feature is assigned to a tyrosine in-plane stretching deformation. [22,23] Additional peaks at 1 672 cm À1 are associated with residual TFA counterions (from the HPLC). [24] There is also a prominent peak in the amide II 0 region at 1 515 cm À1 for this sample.…”

Bio-fabrication and physiological self-release of tissue equivalents using smart peptide amphiphile templates

“…The twofold increase of the average elastic modulus recorded for aligned over non-aligned corneal tissue was probably the result of higher collagen fibre alignment and compaction, density, or cross-linking. Recent studies have demonstrated that the stiffness of fibrillar materials is substantially increased due to anisotropy [26,27]. In addition, similar differences were observed between plastic-compressed collagen gels subjected to different loads [28].…”

Orientation of aromatic residues in amyloid cores: Structural insights into prion fiber diversity

“…In a polymeric matrix the distribution symmetry of oriented fibers is uniaxial and therefore depends only on a single angular coordinate: angle between the fiber and the macroscopic orientation direction. Previous LD studies on amyloid samples, oriented by shear flow, are merely qualitative because the degree of alignment of the fibers could not be quantified (26)(27)(28). Without this orientation parameter it is not possible to deduce how the transition moments of chromophores are oriented in the fiber coordinate framework (Eq.…”

“…1 and Supporting Information). Additional limitations are poor fiber orientation attained by shear flow and significant increase in background scattering by the fibers, resulting in spectra of poor quality (26)(27)(28). By using a structural probe (thioflavin T, ThT) and exploiting the two different mechanisms for fiber orientation-shear-flow in the presence of sucrose and stretched polymer matrix-we attain tyrosine orientation distribution in prion fibers, which represents, to our knowledge, the first detailed, experimentally quantitative information determined by LD of the local organization of amyloids.…”