Application). Protein conformational diseases are now recognized as a major health issue among the increasing aging population. These diseases range from the rare prior-evoked diseases to the more common conditions of Alzheimer's Disease (AD), cataracts and several amyloidosis. Common to most of these diseases is the accumulation of somatic mutations in a normal protein, which leads to inappropriate molecular aggregation, self-assembly and protein deposition in vital organs. Understanding how mutations make a normally soluble protein aggregation-prone is a fundamental goal in fighting protein conformational diseases. These investigators propose to explore this question using Ig light chain, which is known to be associated with several conformational diseases: AL amyloidosis, LCDD and cast nephropathy. The genetic diversity of Ig genes creates thousands of naturally occurring substitutions and many light chain structures have been solved. Therefore, in addition to their own disease significance, the light chains provide a superb system to address how mutations lead to aggregation. This project is a collaboration between a protein chemistry and an immunology group to determine how mutations that are associated with light chain deposition change the folding and/or stability of the protein, and relate these biophysical effects to the fate of the protein in the cell.
Aim 1 is to test the hypothesis that specific destabilizing mutations affect constellations of amino acids, changing the folding of light chain so as to create aggregation-prone surfaces. A newly constructed database of human sequences will be used to identify such mutations based on correlation of clinical and biophysical data. The rarest of these mutations will only be seen in patients if their catastrophic effects are somewhat mitigated by other mutations. These investigators will express recombinant light chains that mimic such mutations, analyze their folding by biophysical methods, and determine their aggregation potential using a newly developed assay.
In Aim 2, the mutants whose folding has been characterized in vitro will be expressed in cells to determine whether they aggregate intracellularly, how they interact with ER chaperones and how and if they are targeted to cellular degradation. Because of their related fold, lessons and predictions derived from studying aggregation-prone light chains should be readily related to the aggregation of other 'Greek key'-type proteins, such as myelin PO, some crystalline, superoxide dismutases, and therefore have broad implications for protein conformation diseases and aging. They hypothesize, as seen with light chains, that most proteins are subject to polymorphisms that enhance or degrade protein stability without overt clinical significance. Such variations, however, are likely to retard, or accelerate, protein degeneration following oxidative stress or other modification, and may influence the rate of appearance of the 'normal' systemic dysfunction during aging.
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