Crystallins

Crystallins are a family of water-soluble structural proteins that constitute the majority of the vertebrate lens. Together they create the high refractive index and transparency required for focusing light on the retina. The lens consists of elongated fiber cells packed with crystallins; as fibers mature, organelles are degraded, and crystallins remain as long-lived, highly concentrated proteins.

There are three major crystallin families: alpha, beta, and gamma. Alpha-crystallins (encoded by CRYAA and CRYAB) function as small heat shock proteins with chaperone activity, helping prevent aggregation of lens proteins under stress. Beta- and gamma-crystallins are primarily structural; beta-crystallins form soluble oligomers, while gamma-crystallins are largely monomeric and contribute to the dense, ordered protein phase in the mature lens.

Crystallin genes include multiple loci in the CRYB and CRYG families, in addition to CRYAA and CRYAB. Expression is largely lens-specific, though some crystallins are also found in other tissues. The lens crystallins are remarkably long-lived and highly stable, characteristics that reduce protein turnover but can accumulate damage over time.

Clinical significance: Mutations in crystallin genes or age-related post-translational modifications (oxidation, deamidation, cross-linking) can reduce solubility and promote light scattering, contributing to cataract formation. Understanding crystallin structure and chaperone function aids studies of lens aging and disease.