Effect Of Beta-sheet-breaker Peptides On The Assembly, Morphology And Mechanical Stability Of Oriented aß25-35 Amyloid Fibrils

Abstract

Amyloid fibrils are self-associating filamentous structures that play an important role in neurodegenerative and protein misfolding diseases. It has been shown that certain peptides, called beta-sheet-breaker (BSB) peptides, may interfere with amyloid fibril assembly. Although BSB peptides are prospective therapeutic agents in amyloidosis, there is ambiguity about the mechanisms and generality of their action.In the present work we analyzed the effect of LPFFD, Soto's BSB peptide, on the growth kinetics, morphological and mechanical properties of amyloid s25-35 (As25-35) fibrils assembled in an oriented array on mica surface. As25-35 is thought to represent the biologically active, toxic fragment of the full-length beta peptide. Growth kinetics and morphological features were analyzed by using in situ AFM in the presence of various concentrations of LPFFD. The mechanical stability of the fibrils was explored with force spectroscopy methods. We found that the addition of LPFFD did not alter the assembly kinetics of As25-35 fibrils. Already formed fibrils did not disassemble in the presence of high concentrations of LPFFD. The nanomechanical behavior of As25-35 fibrils is characterized by the appearance of force plateaus which correspond to the force-driven unzipping of protofilaments. We observed that the plateau force did not change in the presence of LPFFD. The lack of significant effects of LPFFD on As25-35 fibril assembly and stability may suggest that the beta-sheet-breaking effect of the peptide is not general. Alternatively, the As25-35 fibrils formed on mica are in a configuration which is inaccessible to the LPFFD peptide.