Toward Artificial Mussel‐Glue Proteins: Differentiating Sequence Modules for Adhesion and Switchable Cohesion

Sandra Arias,Matthias Pretzler,Shahrouz Amini,Dmitrii Sychev,Justus Horsch,Andreas Fery,Annette Rompel,Hans G Börner,Inga Melnyk

doi:10.1002/ange.202008515

Abstract

AbstractArtificial mussel‐glue proteins with pH‐triggered cohesion control were synthesized by extending the tyrosinase activated polymerization of peptides to sequences with specific modules for cohesion control. The high propensity of these sequence sections to adopt β‐sheets is suppressed by switch defects. This allows enzymatic activation and polymerization to proceed undisturbed. The β‐sheet formation is regained after polymerization by changing the pH from 5.5 to 6.8, thereby triggering O→N acyl transfer rearrangements that activate the cohesion mechanism. The resulting artificial mussel glue proteins exhibit rapid adsorption on alumina surfaces. The coatings resist harsh hypersaline conditions, and reach remarkable adhesive energies of 2.64 mJ m−2 on silica at pH 6.8. In in situ switch experiments, the minor pH change increases the adhesive properties of a coating by 300 % and nanoindentation confirms the cohesion mechanism to improve bulk stiffness by around 200 %.

Highlights

An interference with the tyrosinase activation and polymerization steps was prevented by embedding depsi-switch defects[18] into the (VT)n domain to reduce b-sheet propensity but permit regaining b-sheet formation by minor pH changes
Considering, E = 1.2 GPa of mammalian collagen rich tendon and E % 5–12 GPa reached by Bombyx mori silk fibroin, the artificial mussel glue protein meets an important E-moduli window of highly purpose adapted biomaterials.[32]
The b-sheet formation could be activated by pH-controlled rearrangement of the switch defects as shown by CD spectroscopy and microscopy

Summary

Introduction

Those unimers fuse the Tyr/Cys-bearing segment required for enzymatic polymerization,[16] with a (Val-Thr)n domain to improve cohesion by bsheet formation (Figure 1). An interference with the tyrosinase activation and polymerization steps was prevented by embedding depsi-switch defects[18] into the (VT)n domain to reduce b-sheet propensity but permit regaining b-sheet formation by minor pH changes. These results were expected, due to the high b-sheet tendency of (VT) domains,[20] making handling of unimers and polymers difficult (S.I. Figure S10b).

Results

Conclusion