UNDERSTANDING B-SHEET STRUCTURE IN AQUEOUS SOLUTION

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The long term goal of this research is to understand the chemical principles controlling the folding, stability and self-association of Beta-sheets in peptides and proteins. A Beta-sheet refers to a secondary structure where two or more extended polypeptide chains interact with one another via hydrogen bonding and hydrophobic interactions to create a sheet-like fold. The preparation of small well-defined Beta-sheets has proven to be a very difficult because of their tendency to undergo self- association in competition with, or to the exclusion of, intramolecular folding. The development of a dibenzofuran-based amino acid residue, which directs its neighboring alpha-amino acid residues to fold into an antiparallel Beta-sheet structure, represents a reliable way to create a well-defined Beta-sheet structure in aqueous solution. The ibenzofuran replaces what would normally be a loop or a Beta-turn region and is ideal from the perspective that it does not significantly interfere with the beta-sheet structure. A similar approach has proven useful for creating small parallel Beta-sheets in aqueous solution. This proposal focuses on understanding how the dibenzofuran-based amino acid is able to control the folding of an alpha-amino acid sequence that it is incorporated into. Both low and high resolution spectroscopic methods will be employed to characterize the resulting Beta-sheets and to study the conformation thought to be responsible for rapid folding. Beta-sheet structures that fold cooperatively will be denatured in urea to determine the contributions that the hydrophobic effect or electrostatic interactions make towards either stabilizing or destabilizing the Beta-sheet secondary structure. These sheets will also be used to initiate long term studies to understand Beta-sheet mediated self-assembly. The objectives are to explore the molecular requirements for intermolecular sheet formation and learn how to prevent undesirable sheet-facilitated self-assembly of normally soluble proteins into an insoluble quaternary Beta-sheet structure, known as an amyloid fibril, is thought to be the causative agent in Alzheimer's and related disease. The significance of the work described here is that it is an effort to begin to understand the physical properties of Beta-sheets.