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-β 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 β-sheet networks are the suckerins discovered in the sucker ring teeth of squids. Here, light is shed on the wet adhesion of cross-β 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-β motif, as evidenced using control experiments with disrupted cross-β 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-β motifs are promising biopolymers for wet-resistant adhesion.