Date of Award
Doctor of Philosophy
Environmental Science and Engineering
Protein folding is an important physical process in which the sequences of polypeptides fold into a three-dimensional biological active structure. Misfolding is the conversion of a protein molecule into a structure unlike the native form, and therefore misfolded proteins have a strong tendency to aggregate and make fibrils. Amyloid aggregation is constituted by misfolded amyloidogenic proteins. Neurodegenerative diseases, such as Alzheimer’s Disease (AD), stem from the abnormal accumulation of harmful proteins, including Amyloid-ß peptides, tau protein, and the presynaptic protein α-synuclein in the nervous system. Alzheimer's disease is the most common neurodegenerative disorder that causes memory and learning deficits and is the leading cause of dementia. Therefore, it is evident that clearing amyloid protein aggregates and preventing or interfering with amyloid protein aggregation are the main therapeutic directions for the treatment of Alzheimer's disease. Current commercial drugs are ineffective in treating AD because of various impediments, including difficulties in crossing the blood-brain barrier and instability. Nanomaterials do have huge advantages when targeting amyloid protein aggregation and are able to prevent or dissolve fibrils and protein aggregates. Carbon Nano Materials (CNMs), including Carbon Quantum Dots (CQDs), have found widespread use in biomedical research due to their low toxicity, chemical tunability, and tailored applications. First, we synthesized and characterized carbon quantum dots from gelatin. The same batch of as-synthesized CQDs was used for all experiments. Then we explored the ability of gelatin carbon quantum dots to inhibit fibril formation in a neurodegenerative disorder-associated protein model, Hen-egg white lysozyme (HEWL), using a pulse-chase assay. The addition of gelatin CQDs at different time intervals prevented the formation of HEWL fibrils when added at the beginning and 1 hour after the beginning of the experiment. Moreover, the CQDs introduced 2 and 3 hours after the initiation of fibrillization could alter the morphology and size of the fibrils and result in the formation of smaller and more diverse structures. These observations suggest that gelatin-derived CQDs have a disaggregating effect on the HEWL fibril-forming system. After confirming the therapeutic ability of these carbon-based nanomaterials, we had to ensure their safety for clinical trials. Therefore, we investigated their possible cytotoxicity and apoptotic/necrotic induction at the cellular level using the human neuroblastoma cell line (SH-SY5Y). The findings confirmed the low toxicity of these CQDs with minimal apoptotic/necrotic defects and a high percentage of radical scavenging activity. In addition, since yet there exists a gap in our understanding of the interfacial interactions between biomacromolecules and these novel carbon-centered platforms, we have used gelatin-derived CQDs as a model CNM to examine the impact of this exemplar nanomaterial on two model transporter proteins, apo-myoglobin (apo-Mb), and beta-lactoglobulin (lg). Intrinsic fluorescence measurements revealed that the CQDs induce conformational changes in the tertiary structure of native, partially unfolded, and unfolded states of apo-Mb and lg. Circular dichroism (CD) spectra showed significant differences in secondary structural elements in both native and partially-unfolded apo-Mb and lg which suggest the transition of isolated helices to coiled-coils in the presence and absence of CQDs. Infra-Red spectroscopic data further underscored the interactions between the CQDs and the amide backbone of apo-myoglobin and lg. Notably, the CQDs-driven structural perturbations compromised the binding of heme and retinol to apo-myoglobin and lg, respectively. These results, for the first time, provided an atomic and molecular roadmap of the interplay between carbon-based nanomaterial frameworks and biomacromolecules. These results suggest the prophylactic and therapeutic potential of the developed gelatin-derived CQDs for protein misfolding diseases. Despite their inhibitory impacts on amyloid fibrillation, low cytotoxicity, and high antioxidant activity, the structural perturbations induced by the gelatin-derived CQDs resulted in functional compromises and important findings. Our results clearly suggest that despite the inroads into human health, environment, and agriculture made by carbon nanomaterials in the recent past, it is perhaps necessary to take a step back and define their atomic and molecular impacts on cellular components.
Recieved from ProQuest
Shima Masoudi Asil
Masoudi Asil, Shima, "Carbon Quantum Dots' Effects On The Structure And Function Of Neurodegenerative And Non-Neurodegenerative Associated Proteins" (2023). Open Access Theses & Dissertations. 3823.
Available for download on Sunday, June 08, 2025