The process of protein aggregation is currently very poorly understood despite the increasing public awareness of protein deposition diseases such as Alzheimer's, trans-missible bovine spongiform encephalopathy (mad cow disease), Huntington's disease, and ALS (Lou Gehrig's disease). The purpose of this proposal is to describe the detailed mechanism of protein aggregation specifically leading to the formation of amyloid fibrils. Knowledge of the mechanism of protein aggregation may facilitate the rational design of therapeutic agents to combat or prevent such diseases. A model aggregation system consisting of three recombiant human immunoglobulin light chain (VL) domains will be used to assertain the structure of amyloid fibrils and the mechanism by which they are formed. These objectives will be met using a combination of techniques including site directed mutagenesis, ESI-MS and HPLC/MS/MS, NMR, and TEM (among others). The approaches utilized are designed to give complemetary information that can then be combined to give a complete picture of fibril growth. In vitro inhibitors of amyloid formation and/or fibril elongation will be designed using leads from a combinatorial phage display library.