Impact of point mutations and amino acid modifications on the structure and stability of peptides and proteins probed by FT-IR spectroscopy

Review: model peptides and the physicochemical approach to beta-amyloids

beta-Amyloid peptides are the main protein components of neuritic plaques and may be important in the pathogenesis of Alzheimer's Disease. The determination of the structure of beta-amyloid fibrils poses a challenge because of the limited solubility of beta-amyloid peptides and the noncrystalline nature of fibrils formed from these peptides. In this paper, we describe several physicochemical approaches which have been used to examine fibrils and the fibrillogenesis of peptide models of beta-amyloid. Recent advances in solid state NMR, such as the DRAWS pulse sequence, have made this approach a particularly attractive one for peptides such as beta-amyloid, which are not yet amenable to high-resolution solution phase NMR and crystallography. The application of solid state NMR techniques has yielded information on a model peptide comprising residues 10-35 of human beta-amyloid and indicates that in fibrils, this peptide assumes a parallel beta-strand conformation, with all residues in exact register. In addition, we discuss the use of block copolymers of Abeta peptides and polyethylene glycol as probes for the pathways of fibrillogenesis. These methods can be combined with other new methods, such as high-resolution synchrotron X-ray diffraction and small angle neutron and X-ray scattering, to yield structural data of relevance not only to disease, but to the broader question of protein folding and self-assembly.

Propagating structure of Alzheimer's beta-amyloid(10-35) is parallel beta-sheet with residues in exact register

The pathognomonic plaques of Alzheimer's disease are composed primarily of the 39- to 43-aa beta-amyloid (Abeta) peptide. Crosslinking of Abeta peptides by tissue transglutaminase (tTg) indicates that Gln15 of one peptide is proximate to Lys16 of another in aggregated Abeta. Here we report how the fibril structure is resolved by mapping interstrand distances in this core region of the Abeta peptide chain with solid-state NMR. Isotopic substitution provides the source points for measuring distances in aggregated Abeta. Peptides containing a single carbonyl 13C label at Gln15, Lys16, Leu17, or Val18 were synthesized and evaluated by NMR dipolar recoupling methods for the measurement of interpeptide distances to a resolution of 0.2 A. Analysis of these data establish that this central core of Abeta consists of a parallel beta-sheet structure in which identical residues on adjacent chains are aligned directly, i. e., in register. Our data, in conjunction with existing structural data, establish that the Abeta fibril is a hydrogen-bonded, parallel beta-sheet defining the long axis of the Abeta fibril propagation.