Characterization of the protein fraction of the temporary adhesive secreted by the tube feet of the sea star Asterias rubens

Abstract

Sea stars are able to make firm but temporary attachments to various substrata by secretions released by their tube feet. After tube foot detachment, the adhesive secretions remain on the substratum as a footprint. Proteins presumably play a key role in sea star adhesion, as evidenced by the removal of footprints from surfaces after a treatment with trypsin. However, until now, characterisation was hampered by their high insolubility. In this study, a non-hydrolytic method was used to render most of the proteins constituting the adhesive footprints soluble. After analysis by SDS-PAGE, the proteins separated into about 25 bands, which ranged from 25 to 450 kDa in apparent molecular weight. Using mass spectrometry and a homology-database search, it was shown that several of the proteins are known intracellular proteins, presumably resulting from contamination of footprint material with tube foot epidermal cells. However, 11 protein bands, comprising the most abundant proteins, were not identified and might correspond to novel adhesive proteins. They were named ‘Sea star footprint proteins’ (Sfps). Tandem mass spectrometry analysis of the protein bands yielded 43 de novo-generated peptide sequences. Most of them were shared by several, if not all, Sfps. Polyclonal antibodies were raised against one of the peptides (HEASGEYYR from Sfp-115) and were used in immunoblotting. They specifically labelled Sfp-115 and other bands with lower apparent molecular weights. The different results suggest that all Sfps might belong to a single family of related proteins sharing similar motifs or, alternatively, they are the products of polymerization and/or degradation processes.

Keywords:

• sea stars
• adhesive secretions
• proteins
• mass spectrometry
• immunoblot

Acknowledgements

The authors would like to thank Dr D.S. Hwang for his advice on the manuscript and for his help with amino acid analyses. This work was supported by a FRFC Grant n° 2.4532.07, by the ‘Service Public de Wallonie – Programme Winnomat 2’ and by the ‘Communauté française de Belgique – Actions de Recherche Concertées’. E.H. and P.F. are respectively Postdoctoral Researcher and Senior Research Associate of the Fund for Scientific Research of Belgium (F.R.S.-FNRS). This study is a contribution of the ‘Centre Interuniversitaire de Biologie Marine’ (CIBIM).