Conformations of synthetic β peptides in solid state and in aqueous solution: relation to toxicity in PC12 cells

Abstract

The secondary structures of peptides beta 25-35 (the active toxic fragment) and beta 35-25 (reverse sequence and non-toxic fragment), as well as of the amidated beta (25-35)-NH2 peptide were investigated in aqueous solution and in the solid state by means of Fourier-transformed infrared spectroscopy and circular dichroism spectroscopy. The conformations of the beta 25-35 and beta 35-25 in solid state were identical and contained mostly beta-sheet structures. In solid state the amidated beta (25-35)-NH2 peptide also contained mostly beta-sheet structures. Freshly prepared aqueous solutions of the beta 25-32 (0.5 - 3.8 mM) contained a mixture of beta-sheet and random coil structures. Within 30-60 min incubation at 37 degrees C in water or in phosphate-buffered saline solution (PBS), beta 25-35 was almost fully converted to a beta-sheet structure. Decreasing the temperature from 37 degrees C to 20 degrees C decreased the rate of conversion from random coil to beta-sheet structures, 1-2 h being required for complete conversion. In contrast beta 35-25 in water or in PBS buffer had mostly a random coil structure and remained so for 6 days. The amidated beta(25-35)-NH2 peptide in water (2.7 mM) was also mostly random coil. However, when this peptide (2-2.7 mM) was dissolved in PBS (pH 7.4) or in 140 mM NaCl, a gel was formed and its conformation was mostly beta-sheet. Decreasing the concentration of beta (25-35)-NH2 peptide in 140 mM NaCl aqueous solution from 2 mM to 1 mM or below favored the conversion from beta-sheet structures to random coil structures. The beta 25-35 was toxic to PC12 cells while beta 35-25 was not. The amidated peptide beta (25-35)-NH2 was at least 500-fold less toxic than beta 25-35. Structural differences between these beta peptides in aqueous solutions may explain the difference in their respective toxicities.

The influence of the central region containing residues 19−25 on the aggregation properties and secondary structure of Alzheimer's β‐amyloid peptide

“…When first noted, the neurotoxicity of Aβ-(25Ϫ35) was reported as being reversible by substance P [2]. Whereas a C-terminal methionine amide is an essential feature of the tachykinin family of peptides, Aβ-(25Ϫ35)-amide is much less neurotoxic than Aβ-(25Ϫ35) [27,28]. Nevertheless, in competition assays, Aβ-(25Ϫ35)-amide reduced the deposition of radiolabelled Aβ onto plaques, albeit at concentrations of 10 µM or greater, whereas Aβ-(25Ϫ35) did not [39].…”

“…There is marked sequence similarity between Aβ-(25Ϫ35) and the tachykinin family [2]. However, the tachykinins require a C-terminal amide for activity, whereas Aβ-(25Ϫ35)-amide is much less neurotoxic than the corresponding free acid [27,28]. It would therefore be informative to examine differences in secondary structure of Aβ analogues resulting in a change from free acid to amide.…”

Effects of single and continuous administration of amyloid β-peptide (25–35) on adenylyl cyclase activity and the somatostatinergic system in the rat frontal and parietal cortex

“…The reversal of the amino acid sequence in A␤ (35-25) has been shown to alter the aggregation properties of the peptide from ␤-sheet to random coil formation, thereby reducing the neurotoxic effects on cultured cells (Buchet et al, 1996).…”

New Class of Inhibitors of Amyloid-β Fibril Formation

“…Fibrillization of A␤ occurs via a complex multistep-nucleated polymerization mechanism and proceeds via oligomeric intermediates called protofibrils. The neurotoxicity of A␤ is highly dependent on it's conformation, quaternary structure, and the morphology of the aggregates formed (12)(13)(14)(15). Monomeric A␤ is thought to be not neurotoxic, whereas both protofibrillar and fibrillar species of A␤ exhibit neurotoxicity in cell-based assays (16 -18).…”