Molecular Basis of Osteogenesis Imperfecta

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EXCEED THE SPACE PROVIDED. Osteogenesis imperfecta (OI) usually results from mutations in the two genes, COL1A1 and COL1A2 that encode the chains of type I procollagen, the major structural protein of bone. The most common mutations result in substitutions for glycine residues within the triple helical domain of both chains. Splice site mutations are common and both these classes of mutations often lead to the assembly of molecules with disrupted triple helices. Depending on the location and nature of the disruption, the molecules often have difficulty navigating the secretory pathway because of failure to pass muster in the quality control checkpoints. A much less common class of mutations, those that disrupt the sequences of either chain in the C-terminal propeptide, also interfere with molecular assembly, but prior to or during chain-chain recognition. In contrast to mutations that alter the triple helical sequences, the C-terminal mutations initiate a different array of responses in the cell by activating the synthesis of chaperones, like BiP (GRP78) that bind the abnormal protein. In some instances these proteins are extremely unstable and rapidly degraded, possiblyby proteasomes or by RER-resident proteases. Our aims in this application are to identify additional C- propeptide mutations that alter sequences in both the proa1(1) and proa2(I) chains, to characterize their effects on molecular assembly, examine their distribution in the cell and identify the mechanisms bywhich they are targeted for degradation and then degraded. We will analyze a set of selected cell strains for mutations and then examine the effects on molecular assembly in their home cells. We will then express the C-terminal propeptide with vectors that add antigenic epitopes that are identifiable with available antibodies to examinetheir fate, distribution in the cell, and ability to interact with normal chains in a restricted cellular context. Finally, we will identify the site and means by which these proteins are recognized and then destroyed. These studies should improve our understanding of this disorder and mechanisms by which abnormal proteins are recognized in cells. PERFORMANCE SITE ========================================Section End===========================================