The Importance of the Interfacial Redox In the Mussel Protein Adhesion

Underwater adhesion in the byssus of marine mussels has inspired numerous studies in wet adhesives. The mussel wet adhesion relays on proteins (mfps) rich in the catecholic amino acid 3, 4-dihydroxyphenylalanine (dopa). Dopa is capable of strong interactions with a variety of surfaces, but its susceptibility to oxidation often renders it unreliable for adhesion. Using the Surface Forces Apparatus (SFA) technique, we demonstrate that the adhesion of mussel foot protein 3 (mfp-3) to mica is closely coupled to dopa redox and pH. Increasing the pH to 7.4 decreases the strength of adhesion by an order of magnitude. The mussels eliminate dopa oxidation by secreting the proteins at a confined low pH environment and co-depositing a cysteine-rich protein, mfp-6. Mfp-6 can function as a natural anti-oxidant and preserves the strength of mussel adhesion. Our results demonstrate the importance of the interfacial redox in mussel protein adhesion. The results can help us design better mussel inspired wet adhesives.