This study investigates the single-molecule mechanics of mussel adhesion, focusing on the role of 3,4-dihydroxy-L-phenylalanine (dopa) in binding to both organic and inorganic surfaces. Dopa, a posttranslationally modified form of tyrosine, is essential for the strong adhesion of mussel secreted proteins. Using atomic force microscopy (AFM), the researchers observed a high-strength, fully reversible, noncovalent interaction between a single dopa residue and a wet metal oxide surface. This interaction is not due to hydrogen bonding but rather a unique combination of chemical functionality and strength. Oxidation of dopa, which occurs during the curing of mussel glue, reduces its interaction with metal oxides but leads to high-strength, irreversible covalent bonding with organic surfaces. These findings suggest that dopa plays a critical role in mussel adhesion by exploiting its ability to form strong, reversible bonds with inorganic surfaces and covalent bonds with organic surfaces. The study also reveals that the equilibrium between dopa and its oxidized form, dopa-quinone, allows for adhesion to a wide range of surfaces. On inorganic surfaces, unoxidized dopa forms high-strength, reversible coordination bonds, while on organic surfaces, oxidized dopa forms covalent bonds. The ability of mussels to adhere to both organic and inorganic surfaces is attributed to this equilibrium, which enables interaction with surfaces of varying composition. The study highlights the unique chemical versatility of dopa and its potential applications in the development of bioadhesives and other materials.This study investigates the single-molecule mechanics of mussel adhesion, focusing on the role of 3,4-dihydroxy-L-phenylalanine (dopa) in binding to both organic and inorganic surfaces. Dopa, a posttranslationally modified form of tyrosine, is essential for the strong adhesion of mussel secreted proteins. Using atomic force microscopy (AFM), the researchers observed a high-strength, fully reversible, noncovalent interaction between a single dopa residue and a wet metal oxide surface. This interaction is not due to hydrogen bonding but rather a unique combination of chemical functionality and strength. Oxidation of dopa, which occurs during the curing of mussel glue, reduces its interaction with metal oxides but leads to high-strength, irreversible covalent bonding with organic surfaces. These findings suggest that dopa plays a critical role in mussel adhesion by exploiting its ability to form strong, reversible bonds with inorganic surfaces and covalent bonds with organic surfaces. The study also reveals that the equilibrium between dopa and its oxidized form, dopa-quinone, allows for adhesion to a wide range of surfaces. On inorganic surfaces, unoxidized dopa forms high-strength, reversible coordination bonds, while on organic surfaces, oxidized dopa forms covalent bonds. The ability of mussels to adhere to both organic and inorganic surfaces is attributed to this equilibrium, which enables interaction with surfaces of varying composition. The study highlights the unique chemical versatility of dopa and its potential applications in the development of bioadhesives and other materials.