a.
Crystallins are the most abundant lens proteins, constituting 80 to
90% of the soluble protein of the eye lens.
The abundance and close packing of the crystallins allow the lens to
focus an image onto the retina with minimal distortion and also explain
the transparency of the lens.
Three types of crystallins are identified in mammals, a,
b and g but recently b
and g have been grouped together as
bg crystallins.
The different cystallins differ in their molecular weights and their
ability to aggregates.
The ratio of different crystallins changes with age.
b.
Laminin is a adhesion glycoprotein than forms an integral part of basement
membrane.
It is prominent in basal lamina and underlies epithelium and endothelium.
It is a cross-shaped trimer in which the B1, B2 and A chains form a
triple helix in the stem of the cross.
It is bound tightly to nidogen, a protein that mediates the binding
of laminin to heparin containing proteoglycans.