NIH Research Festival
-Crystallins, monomeric globular proteins, are a key component of the vertebrate eye lens where they exist under conditions of high molecular crowding and essentially no turnover for years. Cataract, the opacification of the lens, is often associated with the formation of crystallin-containing aggregates large enough to scatter light. Insolubilized crystallins from aging and cataractous lenses contain post-translational modifications, including disulfide bonds and isomerized aspartates. S-crystallin (S) is the major member of its family in mammal lenses. In an attempt to capture modified proteins and intermediates in the aggregation process, we screened for crystallization of mouse and chicken S, both wild type and with L/Q variants at position 16 (which are known to have effects on crystallization) under oxidizing conditions. Here we present the structure of an oxidized form of mouse L16 S. The normally monomeric protein has formed an asymmetric octamer consisting of strained, domain-swapped dimers with intra- and intermolecular disulfide bonds and varying degrees of disorder. A central core of interacting N-domains is generally well-ordered, but the outer halo of C-domains shows high disorder, reflected by B-factors, with significant loss of canonical secondary structure. This structure illustrates processes which may contribute to aggregation in the lens. Oxidation, domain-swapping and main-chain strain causes partial unfolding, making the protein vulnerable to further intermolecular interactions.
Scientific Focus Area: Structural Biology
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