8 - Molluscan Collagen and Its Mechanical Organization in Squid Mantle

Abstract

This chapter discusses molluscan collagen and its mechanical organization in squid mantle. Collagen is the principle structural protein in multicellular animals. It is a major component of materials such as the body wall connective tissues of most invertebrates; vertebrate skins; internal organs such as arteries, veins, and guts; and skeletal materials such as bone, tendon, ligaments, and cartilage. In addition, loose connective tissues containing collagen tie together all the other soft internal organs of most animals. Invertebrate tissue collagens are similar to, and evolutionarily related to, vertebrate collagens. Collagen functions as an extracellular protein fiber with a high modulus of elasticity and great tensile strength. These extracellular fibers can be identified by several common characteristics: (1) collagen fibers usually exhibit a 640-Å axial periodicity when observed in the electron microscope; (2) large-angle X-ray diffraction patterns exhibit characteristic reflections that arise from the helical arrangement of the polypeptide chains in collagen fibers; (3) the amino acid composition of collagen is about one-third glycine, and is rich in the imino acids proline and hydroxyproline; and (4) with heating, collagen fibers shrink to about one-third of their original length and become rubbery.