Crystallins are the major structural proteins that make up the eye lens. Two main classes of the crystallin family exist, α and βγ. Alpha-crystallins are responsible for chaperone activity, while βγ-crystallins are primarily structural and affect eye lens development. Damage to crystallins can cause protein misfolding, which in turn leads to protein aggregation and formation of cataract. Investigating the evolution of the vertebrate crystallins will give insight into the structural properties of the lens crystallins and aid in finding ways to prevent cataract formation. The βγ-crystallin of the tunicate Ciona intestinalis split from the vertebrate lineage and has a crystal structure similar to that of the vertebrate βγ-crystallin domain, except for the presence of two calcium-binding sites. This structural similarity has led to the conclusion that the vertebrate βγ-crystallins evolved from these tunicate pre-vertebrate ancestors. We set out to further characterize this tunicate βγ-crystallin and study its Ca2+ binding properties in order to compare and contrast them with those of the vertebrate βγ-crystallins. We found that addition of Ca2+ makes the tunicate crystallin more thermally and chemically stable. Also, the presence of Ca2+ showed structural changes in the tunicate crystallin while no structural changes were observed in the vertebrate crystallin with the addition of Ca2+. We have also solved the solution-state NMR structure of this protein in the presence of Ca2+ and compared it with the solution-state structure of the vertebrate βγ-crystallin domain.

Solution-state NMR structure and biophysical characterization of the Ciona intestinalis βγ-crystallin, an ancestral eye lens protein

251st National Meeting (2016)

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