SULFUR-CENTERED CRYSTALLIN MODIFICATIONS & LENS OPACITY

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DESCRIPTION: Sulfur-centered post-transitional modifications of the crystallins are a recurring feature in many cataractous lenses. This is especially true of maturity-onset human nuclear cataract, in which the cysteine and methionine residues of the beta and gamma crystallins are found to be chemically modified. It is generally assumed that all such modifications are cataractogenic, despite the vast chemical differences between them. In this proposal a strategy is presented to identify the general chemical determinants of cataractogenicity in a variety of crystallin modifications at the cysteine and methionine residues. This strategy is based on the hypothesis that: polar or charged modifications decrease the net attraction between proteins, and are therefore "cataract-inhibiting". Conversely, marginally polar and hydrophobic modifications increase the net attraction between proteins and are therefore "cataractogenic." The following Specific Aims are proposed to test this hypothesis. 1. Introduce in vitro, oxidative modifications normally found in the lens, at the sulfur centers of the beta and gamma crystallins individually and in mixtures, and measure the "cataractogenic" or "cataract-inhibiting" properties of the modified proteins, as defined above. 2. Examine the influence of charge, hydrophilicity and stearic effects on the cataractogenic or cataract-inhibiting tendency of the gamma crystallins and beta-gamma crystallin mixtures modified at the cysteine or methionine residues, using selected chemical modifiers. 3. Evaluate the role of alpha-crystallin and its subunits alpha-A and alpha-B in inhibiting protein aggregation due to sulfur-centered modifications of the gamma crystallins and beta gamma crystallin mixtures. 4. Determine the role of individual cysteine and methionine residues in cataractogenesis by introducing point mutations at these residues using site-directed mutagenesis. The long-term objectives are to devise strategies to prevent cataractogenic modifications in vivo. The proposed studies in Aim 2 are expected to eventually guide the development of anticataract drug candidates. Changes in the net attraction between lens crystallins will be determined by measuring Tph, the phase separation temperature and protein aggregation. SDS-PAGE, size exclusion HPLC, quasielastic light scattering and protein clouding measurements to determine Tph. Ion-exchange HPLC, low pressure chromatography, isoelectricfocusing, Raman and mass spectroscopies will be used as analytical methods for protein characterization. Molecular modeling studies will guide the selection of reagents.