Characterisation of the Carbohydrate Fraction of the Temporary Adhesive Secreted by the Tube Feet of the Sea Star Asterias rubens

Abstract

In sea stars, adhesion takes place at the level of a multitude of small appendages, the tube feet. It involves the secretion of an adhesive material which, after tube foot detachment, remains on the substratum as a footprint. It was previously reported that the two main organic components of this material are proteins and carbohydrates. The carbohydrate moiety of the adhesive secretion of Asterias rubens was investigated using a set of 16 lectins which were used on sections through tube feet, on footprints, and on the proteins extracted from these footprints. After gel electrophoresis, these proteins separate into eight protein bands which were named sea star footprint proteins (Sfps). Eleven lectins label the tube foot epidermis at the level of the adhesive cells, four react with footprints, and eight with two of the extracted footprint proteins, which are therefore classified as glycoproteins. Sfp-290 appears to bear mostly N-linked oligosaccharides and Sfp-210 principally O-linked oligosaccharides. The outer chains of both glycoproteins enclose galactose, N-acetylgalactosamine, fucose, and sialic acid residues. Another part of the carbohydrate fraction of the footprints would be in the form of larger molecules, such as sialylated proteoglycans. These two types of glycoconjugates are presumably key components of the sea star temporary adhesive providing both cohesive and adhesive contributions through electrostatic interactions by the polar and hydrogen-bonding functional groups of their glycan chains.

Sea star tenacity mediated by a protein that fragments, then aggregates

“…In previous studies, the disruption of footprints from the substratum by trypsin treatment demonstrated the crucial role of proteins for adhesion and cohesion (5,18). In the species Asterias rubens, proteins are the main organic components of the adhesive material (20% of the footprint dry weight compared with 8% for carbohydrates and 6% for lipids) (14,16). Recently, we solubilized the majority of these proteins by using denaturing and reducing conditions (14).…”

“…Several unique adhesive proteins have been characterized and assigned specific bulk or surface functions. By comparison, temporary adhesives have been studied to a lesser extent, and, although the presence of specific proteins has been highlighted in some organisms, none has been fully characterized so far (10,13,14).…”

“…In the species Asterias rubens, proteins are the main organic components of the adhesive material (20% of the footprint dry weight compared with 8% for carbohydrates and 6% for lipids) (14,16). Recently, we solubilized the majority of these proteins by using denaturing and reducing conditions (14). Upon gel electrophoresis, they separated into 11 major protein bands in which no homolog proteins were identified by using an MS analysis and homology-database search.…”

“…Upon gel electrophoresis, they separated into 11 major protein bands in which no homolog proteins were identified by using an MS analysis and homology-database search. Proteins in these bands therefore probably correspond to novel adhesive proteins and were named Sea star footprint proteins (Sfps) (14). The labeling of two of these protein bands in lectin blots demonstrated that they contain glycoproteins with oligosaccharide moieties that comprise galactose, GalNAc, fucose, and sialic acid residues (19).…”

“…The labeling of two of these protein bands in lectin blots demonstrated that they contain glycoproteins with oligosaccharide moieties that comprise galactose, GalNAc, fucose, and sialic acid residues (19). Trypsin-digested Sfps were analyzed by tandem MS (MS/MS), which yielded 43 de novo-generated peptide sequences (14).…”