Type 2 diabetes is one of the most prevalent diseases in the United States, inflicting more than 20.8 million people and expanding at epidemic rates in some areas of the country. The key diagnostic of Type 2 diabetes is the presence of amyloid fibers in the pancreas. These fibers are composed of the human islet amyloid polypeptide (hIAPP) and many in vitro and in vivo studies have linked them to the disease. Even so, the mechanism by which hIAPP inhibits pancreatic beta-cell function and insulin production is not understood. A growing body of evidence points to hIAPP interacting with the cell membrane as the cause of cell dysfunction rather than the fibers themselves. One piece of evidence for this hypothesis is that lipid vesicles catalyze fiber formation and in doing so become permeable and leak. Thus, it appears that understanding the disease mechanism requires structural characterization of hIAPP during membrane association, folding, and fiber formation. However, since the mechanism is both kinetic and involves membranes, conventional structural approaches such as NMR are difficult to apply. As a result, almost all experimental structural information comes from circular dichroism measurements, which provide only a rudimentary characterization of the peptide structure. It is not even definitively known which part of the peptide associates with the membrane. Considering the importance of understanding the structural changes of hIAPP with lipid membranes, we propose to use FTIR and 2D IR spectroscopy, in conjunction with 1-13C=18O isotope labeling, to yield site-specific structural information on hIAPP during the kinetics of folding in the presence of lipid vesicles. We will gain residue-level information on peptide association with the membrane, insertion and orientation, secondary structure formation, and test whether pores in the membrane form. The kinetics of structure formation will help reveal the catalytic mechanism for amyloid fiber formation. We seek to obtain a detailed structural characterization of hIAPP membrane catalyzed kinetics that is not currently possible with other techniques. Membrane catalyzed amyloid formation in diabetes studied with 2D IR spectroscopy Membrane catalyzed amyloid formation in diabetes studied with 2D IR spectroscopy.
A clear diagnostic of Type 2 diabetes is the presence of amyloid deposits in the pancreas. Recent research suggests that it is not the deposits themselves that cause the disease, but rather their formation when in contact with pancreatic beta-cells. The aim of this proposal is to better understand the disease mechanism by structurally characterizing how cell membranes catalyze the formation of amyloid deposits, thereby providing basic knowledge that could help in developing pharmaceutical agents to stop the disease.
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