An example of scleroprotein is

Scleroproteins: They are insoluble in water, salt solutions and organic solvents and soluble only in hot strong acids. They form supporting tissues, e.g. collagen of bone, cartilage and tendon; keratin of hair, horn, nail and hoof. Keratin is one of the examples. Reference: Vasudevan 7th  ed, pg 43