NNanomechanical characteristics of proteins and peptides in amyloid

Abstract

......The understanding of the aggregation of amyloid fibrils is essential as they are linked to a number of diseases such as Alzheimer and Parkston’s disease. Amy- loids from different proteins or peptides have common characteristics such as core β-sheet structure, green birefringence upon binding to Congo red, and fibrillar mor- phology. In this thesis, I report single molecule analysis of TTR105−115 a fragment of transthyretin, a serum and cerebrospinal fluid carrier of the thyroid hormone thyroxine (T4) and retinol binding protein bound to retinol. TTR is known to be associated with the amyloid diseases: senile systemic amyloidosis, familial amyloid polyneuropathy and familial amyloid cardiomyopathy. Atomic force microscopy imaging was employed for the study of the morphology and nano mechanical properties of the fibrils in vitro because of it high resolution. TTR105−115 was incubated for 5 days and samples taking at 24 hours interval for AFM imaging. The TTR105−115 fibrils were found to be predominantly straight rigid rods. Splitting of some of the fibrils were observed. A semi automatic software I wrote in Interactive Data Language (IDL) was used for image processing and data analysis. AFM topography height images were used to analyse the nano mechanical properties of the fibrils over time. The measured contour lengths were mostly above one microns though the distribution of the contour lengths were dependent on the length of the incubation time. Profiles along some the fibrils show regular periodicity. The calculated persistence lengths were above one microns varying depending on incubation time. It was found that the mean contour length of the fibrils increases and decreases during the 5 days period of time considered.