Phage Display Screening as a Rational Approach to Design Additives for Selective Crystallization Control in Construction Systems.

The design of additives showing strong and selective interactions with certain target surfaces is key to crystallization control in applied reactive multicomponent systems. While suitable chemical motifs can be found through semi-empirical trial-and-error procedures, bioinspired selection techniques offer a more rationally driven approach and explore a much larger space of possible combinations in a single assay. Here, phage display screening is used to characterize the surfaces of crystalline gypsum, a mineral of broad relevance for construction applications. Based on next-generation sequencing of phages enriched during the screening process, a triplet of amino acids, DYH, is identified as the main driver for adsorption on the mineral substrate. Furthermore, oligopeptides containing this motif prove to exert their influence in a strictly selective manner during the hydration of cement, where the sulfate reaction (initial setting) is strongly retarded while the silicate reaction (final hardening) remains unaffected. In the final step, these desired additive characteristics are successfully translated from the level of peptides to that of scalable synthetic copolymers. The approach described in this work demonstrates how modern biotechnological methods can be leveraged for the systematic development of efficient crystallization additives for materials science.

Subdiffusive Activity Spreading in the Diffusive Epidemic Process.

The diffusive epidemic process is a paradigmatic example of an absorbing state phase transition in which healthy and infected individuals spread with different diffusion constants. Using stochastic activity spreading simulations in combination with finite-size scaling analyses we reveal two qualitatively different processes that characterize the critical dynamics: subdiffusive propagation of infection clusters and diffusive fluctuations in the healthy population. This suggests the presence of a strong-coupling regime and sheds new light on a long-standing debate about the theoretical classification of the system.

Stochastic yield catastrophes and robustness in self-assembly.

A guiding principle in self-assembly is that, for high production yield, nucleation of structures must be significantly slower than their growth. However, details of the mechanism that impedes nucleation are broadly considered irrelevant. Here, we analyze self-assembly into finite-sized target structures employing mathematical modeling. We investigate two key scenarios to delay nucleation: (i) by introducing a slow activation step for the assembling constituents and, (ii) by decreasing the dimerization rate. These scenarios have widely different characteristics. While the dimerization scenario exhibits robust behavior, the activation scenario is highly sensitive to demographic fluctuations. These demographic fluctuations ultimately disfavor growth compared to nucleation and can suppress yield completely. The occurrence of this stochastic yield catastrophe does not depend on model details but is generic as soon as number fluctuations between constituents are taken into account. On a broader perspective, our results reveal that stochasticity is an important limiting factor for self-assembly and that the specific implementation of the nucleation process plays a significant role in determining the yield.

The self-assembly of a large biological molecule from small building blocks is like finishing a puzzle of magnetic pieces by shaking the box. Even though each piece of the puzzle is attracted to its correct neighbours, the limited control makes it very hard to finish the puzzle in a short amount of time. The problem becomes even more difficult if several copies of the same puzzle are assembled in one box. If several puzzles start at the same time, the different parts might steal pieces from each other, making it impossible to successfully complete any of the puzzles. This is called a depletion trap. If the box is only shaken and there is no real control over individual pieces, these traps occur at random. Overcoming these random depletion traps is an important challenge when assembling nanostructures and other artificial molecules designed by humans without wasting many, potentially expensive, components. Previous studies have shown that when multiple copies of the same structure are assembled simultaneously, slowing the rate of initiation increases the yield of correctly-made structures. This prevents new structures from stealing pieces from existing structures before they are fully completed. Now, Gartner, Graf, Wilke et al. have used a mathematical model to show that changing the way initiation is delayed leads to different yields. This was especially true for small systems where fluctuations in the availability of the different pieces strongly enhanced the initiation of new structures. In these cases, the self-assembly process terminated undesirably with many incomplete structures. Nanostructures have various applications ranging from drug delivery to robotics. These findings suggest that in order to efficiently assemble biological molecules, the concentrations of the different building blocks need to be tightly controlled. A question for further research is to investigate strategies that reduce fluctuations in the availability of the building blocks to develop more efficient assembly protocols.

Fish and Clips: A Convenient Strategy to Identify Tyrosinase Substrates with Rapid Activation Behavior for Materials Science Applications.

Peptides with suitable substrate properties for a specific tyrosinase are selected by combinatorial means from a one-bead-one-compound (OBOC) peptide library. The identified sequences exhibit tyrosine residues that are rapidly oxidized to 3,4-dihydroxyphenylalanine (Dopa), making the peptides interesting for enzyme-activated adhesives. The selection process of peptides involves tyrosinase oxidation of tyrosine-bearing sequences on a solid support, yielding dopaquinone residues (fish from the sequence pool), to which thiol-functional fluorescent probes attach by Michael-reaction (clip to mark). Labeled supports are isolated and sequence readout is feasible by MALDI-TOF-MS/MS to reveal peptides, while activation kinetics as well as enzyme-activated coating behavior are verifying the proper selection.

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.

Identification of Functional Peptide Sequences to Lead the Design of Precision Polymers.

Peptide sciences developed dramatically as a result of routine use of solid-phase peptide synthesis and nowadays offer a rich set of well-established strategies to design and identify functional peptide sequences for advanced applications in materials sciences. Appropriate sequences for a wide range of interesting material targets, ranging from molecules to materials surfaces and internal interfaces, can be selected via combinatorial means, and sequence specificities within the resulting peptide-target interactions can be routinely investigated. Based on this understanding, macromolecular sciences can define new polymer structures that meet required functionalities or functional sequences with fully synthetic, nonpeptidic precision polymers to endeavor toward information-based design of next-generation, purpose-adapted macromolecules.

Easy Access to Functional Patterns on Cellulose Paper by Combining Laser Printing and Material-Specific Peptide Adsorption.

Phage display biopanning is used to identify peptides that show material-selective adsorption, effectively distinguishing between the cellulose of paper and the printed toner of standard office laser printers. These genetically selected 12mer peptides can selectively coat either non-printed cellulose or printed toner patterns. Furthermore, triazolindione ligation chemistry is exploited to introduce, for example, dyes or functional peptides selectively to the coatings. The strategy offers an easy access towards the patterned functionalization of paper-based materials, which potentially is of relevance for low-cost diagnostics or biomedical devices.

A direct biocombinatorial strategy toward next generation, mussel-glue inspired saltwater adhesives.

Biological materials exhibit remarkable, purpose-adapted properties that provide a source of inspiration for designing new materials to meet the requirements of future applications. For instance, marine mussels are able to attach to a broad spectrum of hard surfaces under hostile conditions. Controlling wet-adhesion of synthetic macromolecules by analogue processes promises to strongly impact materials sciences by offering advanced coatings, adhesives, and glues. The de novo design of macromolecules to mimic complex aspects of mussel adhesion still constitutes a challenge. Phage display allows material scientists to design specifically interacting molecules with tailored affinity to material surfaces. Here, we report on the integration of enzymatic processing steps into phage display biopanning to expand the biocombinatorial procedure and enable the direct selection of enzymatically activable peptide adhesion domains. Adsorption isotherms and single molecule force spectroscopy show that those de novo peptides mimic complex aspects of bioadhesion, such as enzymatic activation (by tyrosinase), the switchability from weak to strong binders, and adsorption under hostile saltwater conditions. Furthermore, peptide-poly(ethylene oxide) conjugates are synthesized to generate protective coatings, which possess anti-fouling properties and suppress irreversible interactions with blood-plasma protein cocktails. The extended phage display procedure provides a generic way to non-natural peptide adhesion domains, which not only mimic nature but also improve biological sequence sections extractable from mussel-glue proteins. The de novo peptides manage to combine several tasks in a minimal 12-mer sequence and thus pave the way to overcome major challenges of technical wet glues.

Mussel-Glue Derived Peptide-Polymer Conjugates to Realize Enzyme-Activated Antifouling Coatings.

Enzyme-activated polymer coatings based on peptide-polymer conjugates are described. Tyrosinase is used to "switch on" adhesive functions of a mussel-glue derived peptide segment, leading to bioconjugates that adhere to steel. The coating resists seawater treatments and modulates surface properties to antifouling surfaces by strongly reducing protein adsorption.