Biology

Title

Proteolytic Degradation of CTF57 and Abeta Polypeptides by Insulin-Degrading Enzyme: Biophysical Studies with Implications for Alzheimer's Disease

Date of Award

6-2017

Degree Type

Thesis

Degree Name

Master of Science in Biochemistry & Molecular Biology

Department

Biology

Chief Instructor

Noel D. Lazo

Second Reader

Charles Jakobsche

Third Reader

Donald Spratt

Abstract

Alzheimer's Disease (AD) is today's most common type of dementia, affecting approximately 5.4 million Americans. After many years of basic science research and clinical trials, there is still no cure for the disease. We hypothesize that the impaired degradation/clearance of CTF57 and Abeta polypeptides from the brain contributes to the onset of AD. This work expands upon the honor's thesis with emphasis on the proteolytic degradation of these species by insulin-degrading enzyme (IDE). Chapter 3 investigates CTF57's global conformation in solution and its proteolysis using various biophysical techniques. CTF57 forms a reproducible beta-sheet that is non-fibrillar, anti-parallel, and degradable near its C-terminus. Chapter 4 examines the proteolysis of Abeta42 in the presence and absence of polyphenols. According to CD/LC-MS, all Abeta42 samples remain mostly random coil and digestible by IDE. Differences in the degree of fragmentation in the presence of polyphenols, however, imply that small molecules like Resveratrol can facilitate degradation of Abeta42. Importantly, the cleavage sites identified in Chapters 3 and 4 have biological relevance (found in or nearby common motifs) connected to AD pathology and/or the aggregation properties of Abeta species. Chapter 5 provides a qualitative assessment of the effect of small amounts of Abetapyro on the proteolysis of Abeta40/42. Although a similar bulk degradation pattern exists across samples, Ass40 samples remain digestible over 24 hours and show a decrease in NMR peak resolution/intensity as the percentage of Abetapyro increases. Abeta42 samples have stable digestion and lack such peaks or peak changes, indicating that pure Abeta 42 and its Abetapyro mixtures may be more resistant to proteolysis than Abeta40. Together, the results indicate that degradation/clearance of these species likely depends on the substrates' N-termini, the 3D structure within IDE's crypt, and the substrates' positions within the dynamic equilibrium between digestible monomers and higher-order oligomers/assemblies. These findings suggest that identifying therapeutic strategies which sustain IDE enzymatic expression and activity well into old age hold promise for the prevention and treatment of AD.

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