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-? 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 ?-sheet networks are the suckerins discovered in the sucker ring teeth of squids. Here, light is shed on the wet adhesion of cross-? 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, exceeding those measured for all mussel adhesive proteins to date. The pressure-sensitive adhesion of artificial suckerins is largely governed by their cross-? motif, as evidenced using control experiments with disrupted cross-? 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-? motifs are promising biopolymers for wet-resistant adhesion.