The Effect of Oxidation in Mussel Protein Adhesion

Underwater adhesion in the byssus of marine mussels relies on mussel foot proteins (mfps) rich in the catecholic amino acid 3, 4-dihydroxyphenylalanine (dopa). Dopa is a perplexing adhesive adaptation: as a side-chain in synthetic polymers, 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. Raising the pH from 3 to 7.5 decreases the adhesion energy of mfp-3 on mica by a factor of 20 and appears to be driven by the pH-dependent oxidation of dopa in mfp-3. Adding an artifical oxidant, periodate, at pH 3 can also decrease the adhesion of mfp-3 to mica. Our results demonstrate the importance of the oxidation of dopa in mussel protein adhesion.