Polyphosphoprotein-Containing Marine Adhesives
Protein phosphorylation is an important regulator of both cellular and extracellular events. Recently, protein phosphorylation has also emerged as an important process in biological adhesives. During the last decade, Herbert Waite and his group have indeed characterized several polyphosphoproteins from the adhesive secretions of two different marine organisms, mussels and tube-building worms. This suggests the possibility that polyphosphoproteins could be important components of several bioadhesives and may, therefore, be widely distributed throughout the animal kingdom. Many amino acids can be targets for phosphorylation but only phosphoserine (pSer) has been detected to date in marine adhesive proteins. We investigated whether monoclonal antibodies directed against pSer could be used to specifically label polyphosphoproteins in marine adhesives. Antibodies were applied on histological sections through the foot of the mussel Mytilus edulis and through the building organ of the tube-worm Sabellaria alveolata. In both cases, anti-pSer binding was detected in the adhesive glands (phenol gland and cement gland, respectively). However, the intensity of the immunolabeling was different between the two species, being weak in the former and strong in the latter. With the use of these antibodies, a new pSer-rich bioadhesive has been detected in Cuvierian tubules, the sticky defense organs of sea cucumbers. Immunoblots and amino acid analyses confirmed the presence of polyphosphoproteins in the adhesive secretion of the Cuvierian tubules from three species of sea cucumber. These findings bring to three the number of animal groups in which adhesive processes involve polyphosphoproteins and raise interesting questions about the convergent evolution of these adhesives.