Significance of the conformation of building blocks in curing of barnacle underwater adhesive

Abstract

Barnacles are a unique sessile crustacean that attach irreversibly and firmly to foreign underwater surfaces. Its biological underwater adhesive is a peculiar extracellular multi-protein complex. Here we characterize one of the two major proteins, a 52 kDa protein found in the barnacle cement complex. Cloning of the cDNA revealed that the protein has no homolog in the nonredundant database. The primary structure consists of four long sequence repeats. The process of dissolving the protein at the adhesive joint of the animal by various treatments was monitored in order to obtain insight into the molecular mechanism involved in curing of the adhesive bulk. Treatments with protein denaturant, reducing agents and/or chemical-specific proteolysis in combination with 2D diagonal PAGE indicated no involvement of the protein in intermolecular cross-linkage/polymerization, including formation of intermolecular disulfide bonds. As solubilization of the proteins required high concentrations of denaturing agents, it appears that both the conformation of the protein as building blocks and non-covalent molecular interactions between the building blocks, possibly hydrophobic interactions and hydrogen bonds, are crucial for curing of the cement. It was also suggested that the protein contributes to surface coupling by an anchoring effect to micro- to nanoscopic roughness of surfaces. Database -Sequence of Megabalanus rosa cp52k mRNA for 52 kDa cement protein has been submitted to the DNA Data Bank of Japan under accession number. Barnacle attaches irreversibly and firmly to foreign underwater surfaces. Characterization of the major bulk protein at the adhesive joint of the animal indicated no involvement of the protein in the intermolecular cross-linkage/polymerization. It appeared that both conformation of the protein and non-covalent molecular interactions, possibly hydrophobic interactions and hydrogen bonds, are crucial for curing of the adhesive. © 2012 The Authors Journal compilation © 2012 FEBS.