Spongin, a modified type of

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

, forms the fibrous

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

of most organisms among the phylum

Porifera Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a Basal (phylogenetics) , basal clade and a sister taxon of the Eumetazoa , diploblasts. They are sessility (motility) , sessile ...

, the sponges. It is secreted by sponge cells known as spongocytes. Spongin gives a sponge its flexibility. True spongin is found only in members of the class

Demospongiae Demosponges or common sponges are sponges of the class Demospongiae (from + ), the most diverse group in the phylum Porifera which include greater than 90% of all extant sponges with nearly 8,800 species worldwide (according to the World P ...

. Its molecular structure remains incompletely characterized, however it shares similarities with both collagen and keratin.

Research directions

Use in the removal of phenolic compounds from wastewater

Researchers have found spongin to be useful in the photocatalytic degradation and removal of bisphenols (such as BPA) in wastewater. A heterogeneous catalyst consisting of a spongin scaffold for iron phthalocyanine (SFe) in conjunction with

peroxide In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...

and UV radiation has been shown to remove phenolic wastes more quickly and efficiently than conventional methods. Other research using spongin scaffolds for the immobilization of '' Trametes versicolor'' Laccase has shown similar results in phenol degradation.Zdarta, Antecka, Frankowski, Zgoła-Grześkowiak, Ehrlich, and Jesionowski. "The Effect of Operational Parameters on the Biodegradation of Bisphenols by Trametes Versicolor Laccase Immobilized on Hippospongia Communis Spongin Scaffolds." ''Science of the Total Environment'' 615 (2018): 784-95. Web.

Molecular structure

Structure of spongin remains incompletely understood due to limitations in protein analytical methods. Although its chemical composition shares some features with collagen and keratin, spongin is a distinct biopolymer characterized by halogenated amino acids, primary bromine, with smaller amounts of iodine and chlorine. Additionally, the presence of xylose and significant mineralization with calcium carbonates and silica further differentiates spongin from collagen and keratin.

Collagen-like characteristics

Spongin and collagen exhibit comparable filament structure, both displaying a hierarchical organization of nanofibrils, microfibrils, and fibers, as well as a triple-helical based structure. Spongin microfibrilis measure approximately 10nm in diameter and exhibit a periodic banding pattern every 60nm, comparing to collagen's 67nm periodicity. Despite the structural similarities, amino acid analysis reveals that spongin contains significantly higher levels of tyrosine residues, approximately 90% of which are mono- or di-brominated derivatives. This abundance of tyrosine is related to the oxidation of phenylalanine residues, which are prevalent in collagen but nearly absent in spongin. The brominated tyrosine derivatives are hypothesized to play a crucial role in stabilizing spongin's triple-helical structure through cross-linking.

Keratin-like characteristics

Spongin also exhibits compositional similarities to keratin, particularly in its sulfur content and thermal stability. It withstands temperatures up to 300 °C, which is more characteristic for keratin than collagen. However, due to spongin's distinct biochemical features, its full molecular classification remains unknown.

References

Marine biology Collagens {{Biochemistry-stub