Supramolecular β-Sheet Suckerin-Based Underwater Adhesives

Nature has evolved several molecular strategies to ensure adhesion in aqueous environments, where artificial adhesives typically fail. One recently-unveiled molecular design for wet-resistant adhesion is the cohesive cross-beta structure characteristic of amyloids, complementing the well-established surface-binding strategy of mussel adhesive proteins based on 3,4-l-dihydroxyphenylalanine (Dopa). Structural proteins that self-assemble into cross beta-sheet networks are the suckerins discovered in the sucker ring teeth of squids. Here, light is shed on the wet adhesion of cross-beta motifs by producing recombinant suckerin-12, naturally lacking Dopa, and investigating its wet adhesion properties. Surprisingly, the adhesion forces measured on mica reach 70 mN m(-1), exceeding those measured for all mussel adhesive proteins to date. The pressure-sensitive adhesion of artificial suckerins is largely governed by their cross-beta motif, as evidenced using control experiments with disrupted cross-beta domains that result in complete loss of adhesion. Dopa is also incorporated in suckerin-12 using a residue-specific incorporation strategy that replaces tyrosine with Dopa during expression in Escherichia coli. Although the replacement does not increase the long-term adhesion, it contributes to the initial rapid contact and enhances the adsorption onto model oxide substrates. The findings suggest that suckerins with supramolecular cross-beta motifs are promising biopolymers for wet-resistant adhesion.