One Dimensional and Two Dimensional Infrared Spectroscopy of Polyglutamine Aggregates using Protein Synthesis

Extended polyglutamine regions are associated with various neurodegenerative diseases such as Huntington’s disease and Alzheimer’s disease. It is not well understood what causes this aberrant behavior.  The main focus of this research is Huntington’s disease and it’s protein called Huntingtin (Htt), specifically the polyglutamine region of the peptide.  The goal of this research is to understand how and why these peptides behave the way they do. Model peptides of the glutamine region were used to create the K₂Q_xK₂ peptide. The number of glutamines in the peptide are represented the letter “x” such as K₂Q₁₆K₂. Mutations cause the poly Q region of the peptide to extend, self-associate, and aggregate. These mutations cause the polyglutamine to extend to 37 units, which is where the disease develops. The kinetics of this peptide is analyzed to see when and where it begins to aggregate. It is hypothesized that the longer the poly Q chain the more information can be found regarding the cause of the aggregation of the peptide. The goal is to understand why the mutation begins at a particular point in the peptide. The process of synthesizing the peptide K₂Q₂₄K₂ started with isotope labeling on an amino acid called alanine. Isotope labeling was used to track one specific point on the peptide chain, to help us gain accurate information on aggregation in the peptide. After a successful isotope label of alanine the peptide was synthesized. Finally the polypeptide was synthesized and the kinetics and structure were analyzed using 2-D IR spectroscopy.