A
heterogeneous family of water-soluble structural proteins found in
cells of the
vertebrate lens. The presence of these proteins accounts for the transparency of the lens. The
family is composed of four
major groups, alpha, beta, gamma, and delta, and different
minor groups, which are classed on the
basis of size, charge,
immunological properties, and
vertebrate source. Alpha, beta, and delta
crystallins occur in
avian and
reptilian lenses,
while alpha, beta, and
gamma crystallins occur in all another lenses.