Scleroprotein Scleroprotein Scleroproteins or fibrous proteins constitute one of the three main types of proteins (alongside globular and membrane proteins). There are many scleroprotein superfamilies including keratin, collagen, elastin, and fibroin. The roles of such proteins include protection and support, forming connective tissue, tendons, bone matrices, and muscle fiber. A scleroprotein forms long protein filaments, which are shaped like rods or wires. Scleroproteins are structural proteins or storage proteins that are typically inert and water-insoluble. A scleroprotein occurs as an aggregate due to hydrophobic side chains that protrude from the molecule. A scleroprotein's peptide sequence often has limited residues with repeats;
Beta-keratin whose flight capabilities have been questioned, would have had avian, but not feather, β-keratins. The small alvarezsaurid dinosaur "Shuvuuia deserti" shows evidence of a featherlike skin covering. Analysis by Schweitzer "et al." (1999) showed that these featherlike structures consisted of beta-keratin. There are two main forms of keratin, alpha-keratin and beta-keratin. Alpha-keratin is seen in humans and other mammals, beta-keratin is present in birds and reptiles. Beta-keratin is harder than alpha-keratin. Structurally alpha-keratin have alpha-helical coiled coil structure while beta-keratin have twisted beta sheet structure.bIn the case of β-sheets, this allows sterically-unhindered hydrogen bonding between the amino and carboxyl groups