Adhesive and de-adhesive proteins in sea stars

Marine biological adhesives are a promising source for future biomedical applications. They are environmentally friendly, biodegradable, and adhere to various surfaces under wet conditions. Nevertheless, natural adhesives and especially temporary adhesion systems are mostly unexplored. This study is focussed on the characterization of the temporary adhesion in sea stars, in order to provide a new reversible adhesive system for biomimetic approaches. Temporary adhesion in sea stars is based on a duo-gland adhesive system, where adhesive glands secrete the proteinaceous glue and a different gland type produces a de-adhesive substance. It was proposed that the de-adhesive substance contains enzymes to degrade the adhesive proteins, but so far experimental evidence is missing. The first aim of this study is to identify de-adhesive proteins in the sea star Asterias rubens. This would be the first characterization of de-adhesive proteins and would substantially increase our understanding of how voluntary detachment is achieved. Next, we will investigate the adhesive and de-adhesive proteins, carbohydrate moieties, and foot print properties of the sea star Asterina gibbosa. This species was chosen due to its availability, small size, and uncomplicated and fast development within laboratory conditions. The investigation of adhesive components in A. gibbosa allows direct comparison to the distantly related species A. rubens. The gained information in both species will be used to select one adhesive protein for recombinant protein production. This study will severely enhance our knowledge of temporary adhesion and thereby provides one step towards future applications of biomimetic reversible adhesive systems.

Many marine organisms produce biological adhesives for various purposes. These biological adhesives are environmentally friendly, biodegradable, and adhere to various surfaces under extreme conditions. In recent years, there have been growing efforts to develop bio-inspired adhesives. So far, most attempts have been focused on mussel-inspired DOPA-based technologies. However, the temporary adhesion of sea stars could provide a new design paradigm for engineering bio-inspired adhesives and proteinaceous biomaterials. Sea stars adhere strongly but temporarily to underwater substrata via the secretion of a blend of proteins. We found that in the sea star Asterias rubens the secreted adhesive consists of 15 proteins, which serve different functions during attachment. Two proteins are binding to the surface, while the rest is likely providing cohesive strength and forming a binding matrix. Additionally, we identified a proteinase that likely acts as a de-adhesive enzyme. This proteinase presumably weakens the bond between the adhesive material and the tub foot surface during detachment. Furthermore, we investigated if the adhesive protein sequences identified in Asterias rubens are present in 17 additional sea star species, representing different taxa and tube foot morphologies. Our results highlighted a high conservation of the large cohesive proteins making up the structural core of the adhesive, whereas the surface-binding proteins are likely more variable among sea star species. Moreover, we characterized the adhesive secretions of the small starlet cushion sea star Asterina gibbosa in details. The investigation of adhesive components in A. gibbosa allows direct comparison to the distantly related species A. rubens. We found striking similarities in the morphology of tube feet and the topography and composition of the secreted adhesive material. The adhesive proteins are conserved between both species, but the surface-binding proteins in A. gibbosa differ in length and functional domains to A. rubens. The further characterization of the surface-binding proteins is currently ongoing. Overall, our results provide a model for the temporary adhesion of sea stars including a comprehensive list of the involved proteins. We believe our findings are an essential step forward the understanding of echinoderm temporary adhesion but also of marine adhesive systems in general. Moreover, the intriguing underwater adhesive mechanism of sea stars could also pave the way for the development of biomimetic adhesives and coatings.