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Adaptive synergy between catechol and lysine promotes wet adhesion by surface salt displacement

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Science  07 Aug 2015:
Vol. 349, Issue 6248, pp. 628-632
DOI: 10.1126/science.aab0556

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Keeping it sticky when wet

Some biological molecules are remarkably sticky, even to surfaces submerged in water. Mussel adhesion, for example, is based on the overproduction of dihydroxyphenylalanine (DOPA) and proteins with a high abundance of cationic amine residues such as lysine. Using bacterial iron chelators consisting of paired DOPA and lysine groups as analogs for the mussel proteins, Maier et al. show that these two functional groups synergistically enhance interfacial adhesion (see the Perspective by Wilker). The lysine appears to displace hydrated cations from the surface, thus giving a dry patch for better adhesion.

Science, this issue p. 628; see also p. 582

Abstract

In physiological fluids and seawater, adhesion of synthetic polymers to solid surfaces is severely limited by high salt, pH, and hydration, yet these conditions have not deterred the evolution of effective adhesion by mussels. Mussel foot proteins provide insights about adhesive adaptations: Notably, the abundance and proximity of catecholic Dopa (3,4-dihydroxyphenylalanine) and lysine residues hint at a synergistic interplay in adhesion. Certain siderophores—bacterial iron chelators—consist of paired catechol and lysine functionalities, thereby providing a convenient experimental platform to explore molecular synergies in bioadhesion. These siderophores and synthetic analogs exhibit robust adhesion energies (Ead ≥−15 millijoules per square meter) to mica in saline pH 3.5 to 7.5 and resist oxidation. The adjacent catechol-lysine placement provides a “one-two punch,” whereby lysine evicts hydrated cations from the mineral surface, allowing catechol binding to underlying oxides.

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