Date of Graduation
Bachelor of Science in Chemical Engineering
Committee Member/Second Reader
Proteins have various arrays of functions in human bodies. The bio-functions of proteins are depend on their amino acid sequences and folding processes that affect protein structure. While most of proteins fold in their own pathways, some of them misfold and aggregate due to mutations caused by various reasons. These aggregations are believed to be main causes of protein conformation disorders like Alzheimer's disease, Type II diabetes, Huntington's disease, and prion disease. An aggregated form of amyloid beta is considered as a hallmark of Alzheimer's disease. Amyloid beta develops from oligomer into a fibril as the aggregation process proceeds. The fibrils interrupt communications between brain cells. In a previous research (Dr. Servoss, et al.) it was proven that the aggregation of amyloid beta can be inhibited by a peptoid that mimics a sequence of amyloid binding sight (KLVFF). The peptoid (JPT1) successfully inhibited both beta sheet and fibril formation of amyloid beta in vitro. In this experiment, two variants of JPT1 were synthesized to observe how the structure of JPT1 affect the aggregation of amyloid beta: side chain rearrangement (JPT1s), achiral form (JPT1a). Amyloid beta samples were treated with the variants of JPT1 and compared with one treated with JPT1. Both beta sheet and fibril structures of amyloid beta were detected through ThT assay and dot blots respectively. In a result, JPT1a was characterized with higher inhibition rates against both beta sheet structures and fibrils than those of JPT1. While JPT1a showed a significant improve in inhibition rate, JPT1s did not show a noticeable difference with JPT1 in inhibiting amyloid beta aggregation. Later, it was observed that the amyloid beta samples, which are treated with JPT1a, took a different pathway in aggregation process. They were developed into high ordered oligomers instead of fibrils. This result implies that the the chiral structure of JPT1 plays a critical role in inhibiting amyloid beta aggregations.
Type 2 diabetes (T2D) is a disease that is characterized with a protein misfold. T2D brings a disorder in absorbing IAPP in a pancreatic beta cell. A protein IAPP (Islet Amyloid Polypeptide), also known as amyline, is related with suppression of food intake and gastric emptying. It is believed that the fibril forms of amylin contributes to the aggravation of pancreatic disorder as they aggregate. Although amylin has different amino acid sequences with amyloid beta, its folding mechanism is similar with that of amyloid beta protein. Amylin forms into a fibril form via beta sheet structure due to misfold. This research was conducted to observe whether JPT1 can inhibit the aggregation of amyloid beta by interrupting pi-pi stacking of beta structures. Different concentrations of JPT1 (0, 40, 100, 200 μM) were added to amylin samples and incubated on an orbit shaker. Both aminated and free acid versions of amylin were tested since the ratio between two amylin is not well understood yet. Before ThT assay, competition assay was proceeded to ensure that the JPT1 does not affect the binding sight of ThT and amylin. Through ThT data and TEM images, clear decreases of amylin beta sheet structure and fibril were observed. However, an increase in beta sheet formation was detected as a high concentration (200 μM ) of amylin was added to free acid amylin. The TEM image of free acid amylin treated with 200 μM of JPT1 suggested a new morphology of amylin aggregation. The experimental data concludes that JPT1 can inhibit amylin aggregation It is also observed that the high concentration of inhibitor can lead to different morphology of aggregates. This results correlates to the previous research where JPT1a inhibited beta sheet structures and fibrils form of amyloid beta effectively, but changed the protein into a high ordered oligomer form,
Park, D. (2016). Peptoid morphology studies and its performance in inhibiting islet amyloid polypeptide. Chemical Engineering Undergraduate Honors Theses Retrieved from https://scholarworks.uark.edu/cheguht/87