BIGH3 WILD TYPE AND MUTANT PROTEINS

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Several corneal dystrophies [granular corneal dystrophy (GCD), lattice corneal dystrophy (LCD) types I and IIIA, combined UCD-LCD type I, Thiel-Behnke dystrophy and Reis-Bucklers dystrophy] have been found to result from mutations in BIGH3. These conditions are characterized by the deposition within the cornea of proteins that react with antibodies to beta-ig-h3 (the protein product of the BIGH3 gene). For each dystrophy the accumulations have a characteristic ultrastructure. This proposal is to purify and characterize beta-ig-h3 from plasma of persons with and without different BIGH3 corneal dystrophies and from cell cultures of COS- 7, CHO-K1 and baculovirus infected insect cells transfected with vectors containing the mutations that produce BIGH3 corneal dystrophies. Wild-type and mutant beta-ig-h3 proteins will be compared to test the hypothesis that the structure of the proteins that accumulate within the cornea in the BIGH3 corneal dystrophies are related to the mutated protein and that a relationship exists between different phenotypes and the BIGH3 genotypes and between the amount of the mutant protein that is expressed. The nature of the amyloid that accumulates in certain BIGH3 corneal dystrophies and the reason for its production will be investigated. We will determine whether BIGH3 related amyloid is a specific fragment of mutant beta-ig-h3. Because beta-ig-h3 interacts with components of the extracellular matrix we will attempt to identify protein- protein interactions that may account for the accumulations that characterize the BIGH3 corneal dystrophies. The biosynthesis of beta-ig-h3 will be characterized in rabbit corneal epithelial cells.