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

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

Muschel-inspirierte Polymerisation: Synthetische Bioadhäsive für wasserbasierte Klebstoffe und meerwasserresistente Beschichtungen

Miesmuscheln inspirieren zur nächsten Generation von wasserbasierten Nassklebstoffen. Muschelfußproteine (mfps) ermöglichen es den Muscheln, sich an jede Oberfläche zu haften und zeigen bemerkenswerte Eigenschaften, die insbesondere durch das Aminosäurederivat 3,4 Dihydroxyphenylalanin (Dopa) verursacht werden. Da der Einfluss von Wasser nach wie vor eine große Herausforderung für Klebeanwendungen darstellt und die Herstellung und Reinigung von Klebeproteinen viel Zeit und Kosten erfordert, ist ein einfacher Zugang zu biomimetischen Klebstoffen von großem Interesse. Die vorliegende Arbeit untersucht einen neuartigen Muschel-inspirierten Polymerisationsansatz zur Herstellung von adhäsiven Proteinanaloga aus Oligopeptiden (Unimeren). Der Polymerisationsmechanismus nutzt einen Reaktionsweg, der in Miesmuscheln auftritt und beruht auf einer enzymatischen Oxidation von Tyrosin zu Dopachinon, das mit freien Thiolen aus Cystein Cysteinyldopa bildet, wodurch Unimere verknüpft und adhäsive Funktionalitäten erzeugt werden. Innerhalb weniger Minuten entstehen hochmolekulare Polymere, die ein vielseitiges Adsorptions- und starkes Adhäsionsverhalten demonstrieren. Die Proteinanaloga weisen eine signifikante Multischicht-Adsorption auf hydrophilen sowie hydrophoben Oberflächen auf und sind resistent gegenüber Spülschritten mit hochkonzentrierten Salz-Lösungen. Die beobachteten Adhäsionsenergien liegen im Bereich von kommerziellen mfp-Extrakten und überschreiten sogar berichtete Werte für isolierte mfps. Die Arbeit präsentiert eine einfache Synthese künstlicher mfp-Analoga, die in der Lage sind Aspekte natürlicher mfps nachzuahmen und potenziell zur Entwicklung von wasserresistenten Universalklebstoffen beitragen. Um die Bedingungen für eine kostengünstige, großtechnische Produktion zu verbessern, werden zusätzlich alternative Synthesewege für die enzymfreie Herstellung Muschel-inspirierter Polymere untersucht, die auf der chemischen Oxidation von Dopa-haltigen Unimeren beruhen.Marine mussels provide inspiration for the next generation of water-based, wet adhesives. Mussel foot proteins (mfps) enable them to attach to any surface and exhibit remarkable properties, notably due to the amino acid derivative 3,4-dihydroxyphenylalanine (Dopa). Since the influence of water still constitutes a major challenge for gluing applications and large-scale production and purification of adhesive proteins is time-consuming and costly, an easy access route toward biomimetic adhesives is of high interest. This thesis investigates a novel mussel-inspired polymerization approach for the production of adhesive protein analogues from oligopeptides (unimers). The polymerization mechanism exploits a distinct reaction pathway, occurring in mussels and relies on enzyme-mediated oxidation of tyrosine to Dopaquinone in the unimers, which forms cysteinyldopa with free thiols from cysteine, thereby linking unimers and generating adhesive moieties. Within a few minutes high molecular weight polymers are obtained that show versatile adsorption and strong adhesion behaviour. The protein analogues exhibit significant multilayer adsorption onto hydrophilic as well as hydrophobic surfaces and resist rinsing with highly saline solutions. Comparative adhesion studies on silica reveal adhesion energies that are in the same range as commercial mussel foot protein extracts and even exceed reported values for isolated foot proteins that constitute the gluing interfaces. The approach offers facile access toward artificial mussel foot proteins that are capable of mimicking aspects of the natural ideal and potentially helps to develop next-generation universal water resistant glues. In order to further improve the conditions regarding cost-efficient and large-scale production in the future, alternative synthesis routes for the enzyme-free generation of mussel-inspired polymers based on chemical oxidation of Dopa containing unimers are additionally explored

Mussel-Inspired Polymerization of Peptides

A previously introduced tyrosinase‐activated polymerization of Tyr‐ and Cys‐bearing peptides yielding artificial mussel‐glue proteins is realized without the need of the specific enzyme by a chemical activation route. This decouples the sequence of polymerizable peptides (unimers) from the constraints of tyrosinase substrates and enables the polymerization of minimal motifs such as Dopa‐Lys‐Cys (Umini*KC) or Dopa‐Gly‐Cys (Umini*GC). In the polymerization procedure, sodium periodate is used to oxidize Dopa residues of the unimers to Dopa‐quinones to which the thiol of a Cys residue is added in a Michael‐type reaction. The resulting polyUmini*KC and polyUmini*GC exhibit a thiol–catechol connectivity as a potent adhesive functionality at each repeat unit. QCM‐D experiments show the excellent substrate adsorption properties of the products from the chemically activated polymerization. On aluminum oxide surfaces, polyUmini*KC rapidly forms a coating, even under seawater model conditions and the coating resists rinsing with hypersaline solution of 4.2 M salt mixtures. While the sodium periodate oxidation is less specific than the tyrosinase reaction and requires the implementation of Dopa instead of Tyr residues into the polymerizable unimers, the chemical route makes scale‐up more easily accessible.Peer Reviewe

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

The synthesis of artificial mussel‐glue proteins with pH triggered cohesion control mechanism is described by extending the tyrosinase activated polymerization of peptides to sequences having specific modules for cohesion control. The high propensity of those sequence sections to adapt β‐sheets is temporarily suppressed by switch defects. This allows enzymatic activation and polymerization to proceed undisturbed. The β‐sheet formation is regained after polymerization by changing pH from 5.5 to 6.8, 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 ~200%