The unique neuropathologic abnormality in Alzheimer's disease is the high density of neurofibrillar plaques which are formed by the deposition of a subset of peptides and protein fragments inside and outside of neural cells. Among these peptides is a 42 residue fragment of a larger protein, 771 residues in length, termed amyloid precursor protein (APP). At the present time there is little understanding of the molecular events in the formation of these neurofibrillar plaques. A transmembrane region of APP constitutes part of the amyloid protein found in plaques. Furthermore, little information is currently available to address the manner in which APP, a cell surface protein, is normally translocated, folded and assembled with its molecular partners in the cell. APP is likely synthesized and translocated through the normal secretory pathway of the cell. This requires the active participation of molecular chaperones to mediate correct folding and assembly events. The role of these protein folding catalysts in the biogenesis of APP becomes significant with the observation that a member of the protein chaperone family, a homologue of E. coli dnaJ, is associated with neurofibrillar plaques from Alzheimer's tissues. In the proposed studies, we shall directly examine the interaction of eukaryotic members of the E. coli dnaK, dnaJ and grpE (KJE) family of molecular chaperones with unfolded proteins and purified APP. Using purified eukaryotic members of this family, including the neuro specific dnaJ homologue from neurofibrillar plaques, we shall establish the order of addition, mechanism and energetics of the association of the chaperones with APP and also examine the regions of APP which may serve as targets for the binding of members of the KJE homologous. In preliminary studies, we have demonstrated that the neuro specific dnaJ homologue termed HSJ1 can replace the essential homologous protein in the simple eukaryote, Saccharomyces cerevisiae to restore viability to cells. To examine the in vivo consequences of limiting chaperone action on APP aggregation and processing in cells, we shall establish a model system in yeast to express either full length APP or portions associated with neurofibrillar ,plaques in cells harboring conditional mutations in components of the KJE family. These combined studies would provide the first direct test of the extent to which these molecular chaperones participate in normal APP biogenesis and if a reduced role for protein folding catalysts might accelerate amyloid plaque formation.
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