Identification of proteins associated with adhesive prints from Holothuria dofleinii Cuvierian tubules

Cuvierian tubules are expelled as a defence mechanism against predators by various species within the family Holothuridae. When the tubules are expelled, they become sticky almost immediately and ensnare the predator. The mechanism of this rapid adhesion is not clear, but proteins on the surface of the expelled tubules are widely believed to be involved. This study has examined such proteins from Holothuria dofleinii, sourced from adhesive prints left on glass after the removal of adhered tubules. Gel electrophoresis showed that seven strongly staining protein bands were consistently present in all samples, with molecular masses ranging from 89 to 17 kDa. N-terminal sequence data was obtained from two bands, while others seemed blocked. Tandem mass spectrometry-based sequencing of tryptic peptides derived from individual protein bands indicated that the proteins were unlikely to be homopolymers. PCR primers designed using the peptide sequences enabled us to amplify, clone and sequence cDNA segments relating to four gel bands; for each, the predicted translation product contained other peptide sequences observed for that band that had not been used in primer design. Database searches using the peptide and cDNA-encoded sequences suggest that two of the seven proteins are novel and one is a C-type lectin, while-surprisingly-at least three of the other four are closely related to enzymes associated with the pentose phosphate cycle and glycolysis. We discuss precedents in which lectins and metabolic enzymes are involved in attachment and adhesion phenomena.