UC Irvine

Crystallins are water-soluble proteins that are necessary for focusing light on the retina. In mammalian lenses, there are two classes of crystallins; α-crystallins (molecular chaperone proteins), and βγ-crystallins (structural proteins). My research has focused on $\gamma$S-crystallin, which is the main structural component of the human eye lens cortex and contributes to the lens fiber organization. Present up to 450 mg/mL in the human lens, γS-crystallin depends on its long-term ability to remain stable and retain a high refractive index. The G18V variant of γS-crystallin (γS-G18V), associated with hereditary childhood-onset cataract, shows decreased stability and increased aggregate formation. My work explores the intermolecular interactions contributing to the increased aggregation propensity of γS-G18V relative to wild-type (γS-WT). By titration of a hydrophobic chemical probe (ANS) and by titration of tripeptides (a library composed of the crystallin sequence), residue-specific binding was observed via NMR chemical shift perturbations (CSP). Protein-protein interactions have also been measured for the direct determination of the second virial coefficient, which describes the intermolecular interactions as being either repulsive or attractive. The second virial coefficient for lysozyme under physiological conditions will give better insight into how the individual molecules are interacting with one another in solution. The control experiments with lysozyme will be applied to both γS-WT and a deamidated variant, N15D, to investigate how prone the crystallins are to aggregation. Additionally, in order to investigate the functionality of crystallins from aquatic species, the biophysical characterization of the J2-crystallin from box jellyfish (Tripedalia cystophora) will be presented. J2-crystallin is an excellent example of convergent evolution developing a protein to perform the refractive function needed in the eye lenses and thus a deeper understanding of how these crystallins are related to one another. Lastly, the refractive index increment (dn/dC) of various crystallins from aquatic and terrestrial species will be reported to fully understand the functionality of the eye lens.