Polymerizing Like Mussels Do: Toward Synthetic Mussel Foot Proteins and Resistant Glues

Abstract

A novel strategy to generate adhesive protein analogues by enzyme-induced polymerization of peptides is reported. Peptide polymerization relies on tyrosinase oxidation of tyrosine residues to Dopaquinones, which rapidly form cysteinyldopa-moieties with free thiols from cysteine residues, thereby linking unimers and generating adhesive polymers. The resulting artificial protein analogues show strong adsorption to different surfaces, even resisting hypersaline conditions. Remarkable adhesion energies of up to 10.9 mJ m^-2 are found in single adhesion events and average values are superior to those reported for mussel foot proteins that constitute the gluing interfaces.

Keywords: adhesives; enzyme-induced polymerization; mussel glue; synthetic protein mimics; tyrosinase activation.

Figure 1

Principle of mussel‐inspired polymerization. i) An amino acid sequence is abstracted from Mefp‐1 and extension with Cys leads to the unimer U₁ ^C. ii) Polymerization of U₁ ^C can be triggered by enzymatic oxidation of tyrosine to Dopaquinone, which reacts with thiol moieties of Cys residues, enabling the formation of cysteinyldopa linkages. iii) The obtained mfp analogues exhibit strong adhesion to various substrates, making them useful for coatings or glues.

Figure 2

Enzyme‐activated polymerization of U₁ ^C by tyrosinase to form polyU₁ ^C (a,b) and model study revealing kinetics of tyrosinase‐induced dimerization of U₁ ^S and U_1N ^C (c,d). MALDI‐TOF‐MS of U₁ ^C at time zero (a) and of polyU₁ ^C after 10 min (b, left). GPC traces of polyU₁ ^C (b, right). c) Reaction pathway for the model dimerization shows enzymatic oxidation of tyrosine in U₁ ^S to Dopaquinone (i  a,b), U_1N ^C oxidation to disulfide by Dopaquinone reduction and the inverse reaction (ii) as well as U_1N ^C‐U₁ ^S dimer formation by cysteinyldopa linkage (iii). d) Relative concentrations of different species during model dimerization determined by HPLC kinetics. (Conditions: 0.25 mm of U₁ ^S and 0.26 mm U_1N ^C (1/1.05, v/v) in pH 6.8 buffer, 50 U mL⁻¹ AbPPO4).

Figure 3

Adsorption (a) and adhesion (b) behavior of polyU₁ ^C and polyU₂ ^C. a) QCM‐D adsorption and desorption kinetics of mfp analogues on Al₂O₃ coated sensors (incubation step and subsequent buffer rinsing (left) and stability tests of the coatings (right) by washing with 599 mm NaCl (I) and 4.2 m hypersaline solution (ΙΙ)). b) Adhesive properties of mfp analogue determined by colloidal probe AFM. Illustration of the CP‐AFM contact analysis (left) and work of adhesion per unit area of polyU₁ ^C coatings in dependence of the dwell time (right; substrates were coated for 1 h (blue), for 2 h (green) and 1 h+post‐treatment with sodium ascorbate (red); constant load force of 2 nN; lines are to guide the eye only).