Amyloid-like conformation and interaction for the self-assembly in barnacle underwater cement

Barnacles are unique marine sessile crustaceans and permanently attach to various foreign surfaces during most of their lifespan. The protein complex secreted from their body and used to attach their calcareous shell to almost all surfaces in water has long fascinated us because we have limited technology with which to attach materials in water. Unraveling the mechanism of underwater attachment by barnacles is thus important for interface science, for the understanding of the biology and physiology of barnacles, and for the development of technology to prevent fouling. Previous studies have indicated that the intermolecular interactions optimized by conformations of the adhesive proteins are crucial in the self-assembly and/or curing of the adhesive. This study aimed to identify the possible structural determinants responsible for the self-assembly. Thioflavin T binding screening of peptides designed on the basis of the primary structure of a bulk 52 kDa cement protein indicated the presence of some amyloidogenic motifs in the protein. The conformation of the peptide was transformed to a β-sheet by an increase in either pH or ionic strength, resulting in its self-assembly. Thioflavin T binding was inhibited by small polyphenolic molecules, suggesting the contribution of aromatic interactions during self-assembly. The occurrence of amyloid-like units in the protein implies that the protein conformation is an important factor contributing to the self-assembly of the cement, the first event of the curing, as the adhesive material is secreted into the seawater out of the animal's body.