Marine invertebrate collagens: The prevalence of type V and XI like collagens in some marine crustacean and molluscan tissues

While the invertebrates constitute almost 95% of the animal kingdom, our kn owledge on their extracellular matrices, particularly on collagen, is very scanty. Our group has been studying the collagen polymorphism in some marin e invertebrate tissues with focus on structure-function relationships and m olecular evolution. We have established methods to purify unique collagen m olecules from some rare tissues of crustaceans and molluscs. Some of these include the intramuscular tissues of the crustaceans and the cartilage and cornea of molluscs. The biochemical parameters in these tissues relating to collagen content, solubility and carbohydrate composition have been determ ined. The chain composition of these collagens were deduced by SDS-PAGE. We have analyzed the amino acid compositions of these collagens and that of i solated single alpha chains. The physicochemical properties and ultrastruct ural characteristics of some of these collagens were also studied. The resu lts indicate that the principal component of crustacean muscle is a type V like homotrimer and that of molluscan cartilage and cornea is a unique hete romeric collagen resembling vertebrate type V and XI collagens. These colla gens were invariably highly crosslinked, stabilized largely by bound carboh ydrates and had significantly high denaturation temperatures. While the cru stacean type V collagen formed regularly banded fibrils, the V/XI like coll agen of molluscan cartilage lacked periodicity in fibril structure. We corr elate the significance of our key observations to the possible functional c onsequence as well as evolutionary significance, based on the available dat a on other similar collagens.