Elastic and pH-Responsive Hybrid Interfaces Created with Engineered Resilin and Nanocellulose

Synthetic biology-guided design and biosynthesis of protein polymers for delivery

Vehicles derived from genetically engineered protein polymers have gained momentum in the field of biomedical engineering due to their unique designability, remarkable biocompatibility and excellent biodegradability. However, the design and production of these protein polymers with on-demand sequences and supramolecular architectures remain underexplored, particularly from a synthetic biology perspective. In this review, we summarize the state-of-the art strategies for constructing the highly repetitive genes encoding the protein polymers, and highlight the advanced approaches for metabolically engineering expression hosts towards high-level biosynthesis of the target protein polymers. Finally, we showcase the typical protein polymers utilized to fabricate delivery vehicles.

Production of bovine beta-lactoglobulin and hen egg ovalbumin by Trichoderma reesei using precision fermentation technology and testing of their techno-functional properties

The food protein ingredient market is dominated by dairy and egg proteins. Both milk whey and egg proteins are challenging proteins to replace, e.g. with plant proteins, due to the unique structural features of the animal proteins that render them highly functional. Thus, to provide a non-animal source of these important proteins the fungal host Trichoderma reesei was utilized for the biotechnical production of recombinant hen ovalbumin (TrOVA) and bovine beta lactoglobulin (TrBLG). These food proteins were investigated using two different promoter systems to test the concept of effectively expressing them in a fungal host. Both proteins were successfully produced in 24 well plate and bioreactor scale. The production level of TrBLG and TrOVA were 1 g/L and 2 g/L, respectively. Both proteins were further purified and characterized, and their functional properties were tested. TrBLG and TrOVA secondary structures determined by circular dichroism corresponded to the proteins of bovine and hen. The T. reesei produced proteins were found to be N-glycosylated, mostly with Man 5. TrBLG had emulsification properties matching to corresponding bovine protein. TrOVA showed excellent foaming characteristics and heat-induced gelation, although the strength of the gel was somewhat lower than with hen ovalbumin, possibly due to the partial degradation of TrOVA or presence of other host proteins. Biotechnical production of whey and egg proteins using precision fermentation technology offers an innovative way to increase the sustainability of the conventional food industry, without further reliance on animal farming. Industrial relevance: The food protein ingredient market is dominated by dairy (largely whey proteins) and egg proteins. Whey proteins are valuable and versatile food ingredients due to their functional and nutritional quality. They are largely used in meat and milk products, low fat products, bakery, confectionary, infant formulas and sports nutrition. Similarly, egg white protein ovalbumin is a highly functional protein ingredient that facilitates structure formation and high nutritional quality in most food products. Together they comprise 40-70% of the revenue in the animal protein ingredients market. Both whey and egg proteins are extremely challenging proteins to replace, e.g., by plant proteins due to their unique structural features that render them with high functionality. Biotechnical production of whey and egg proteins using precision fermentation technology offers an innovative way to increase the sustainability of the conventional food industry, without further reliance on animal farming.

Emergence of Elastic Properties in a Minimalist Resilin-Derived Heptapeptide upon Bromination

Bromination is herein exploited to promote the emergence of elastic behavior in a short peptide-SDSYGAP-derived from resilin, a rubber-like protein exerting its role in the jumping and flight systems of insects. Elastic and resilient hydrogels are obtained, which also show self-healing behavior, thanks to the promoted non-covalent interactions that limit deformations and contribute to the structural recovery of the peptide-based hydrogel. In particular, halogen bonds may stabilize the β-sheet organization working as non-covalent cross-links between nearby peptide strands. Importantly, the unmodified peptide (i.e., wild type) does not show such properties. Thus, SDSY(3,5-Br)GAP is a novel minimalist peptide elastomer.

Tag-mediated single-step purification and immobilization of recombinant proteins toward protein-engineered advanced materials

Background

The potential applications of protein-engineered functional materials are so wide and exciting that the interest in these eco-friendly advanced materials will further expand in the future. Tag-mediated protein purification/immobilization technologies have emerged as green and cost-effective approaches for the fabrication of such materials. Strategies that combine the purification and immobilization of recombinant proteins/peptides onto/into natural, synthetic or hybrid materials in a single-step are arising and attracting increasing interest.

Aim of Review

This review highlights the most significant advances of the last 5 years within the scope of tag-mediated protein purification/immobilization and elucidates their contributions for the development of efficient single-step purification and immobilization strategies. Recent progresses in the field of protein-engineered materials created using innovative protein-tag combinations and future opportunities created by these new technologies are also summarized and identified herein.

Key Scientific Concepts of Review

Protein purification/immobilization tags present a remarkable ability to establish specific non-covalent/covalent interactions between solid materials and biological elements, which prompted the creation of tailor-made and advanced functional materials, and of next-generation hybrid materials. Affinity tags can bind to a wide range of materials (of synthetic, natural or hybrid nature), being most suitable for protein purification. Covalently binding tags are most suitable for long-term protein immobilization, but can only bind naturally to protein-based materials. Hybrid affinity-covalently binding tags have allowed efficient one-step purification and immobilization of proteins onto different materials, as well as the development of innovative protein-engineered materials. Self-aggregating tags have been particularly useful in combination with other tags for generating protein-engineered materials with self-assembling, flexible and/or responsive properties. While these tags have been mainly explored for independent protein purification, immobilization or functionalization purposes, efficient strategies that combine tag-mediated purification and immobilization/functionalization in a single-step will be essential to guarantee the sustainable manufacturing of advanced protein-engineered materials.

Resilin-mimetics as a smart biomaterial platform for biomedical applications

Intrinsically disordered proteins have dramatically changed the structure-function paradigm of proteins in the 21st century. Resilin is a native elastic insect protein, which features intrinsically disordered structure, unusual multi-stimuli responsiveness and outstanding resilience. Advances in computational techniques, polypeptide synthesis methods and modular protein engineering routines have led to the development of novel resilin-like polypeptides (RLPs) including modular RLPs, expanding their applications in tissue engineering, drug delivery, bioimaging, biosensors, catalysis and bioelectronics. However, how the responsive behaviour of RLPs is encoded in the amino acid sequence level remains elusive. This review summarises the milestones of RLPs, and discusses the development of modular RLP-based biomaterials, their current applications, challenges and future perspectives. A perspective of future research is that sequence and responsiveness profiling of RLPs can provide a new platform for the design and development of new modular RLP-based biomaterials with programmable structure, properties and functions.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the effort toward sustainable advanced functional materials, nanocelluloses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entangled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modifiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional properties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, biological scaffolding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected perspectives toward new directions for sustainable high-tech functional materials science based on nanocelluloses are described.

Novel genetic tools that enable highly pure protein production in Trichoderma reesei

Trichoderma reesei is an established protein production host with high natural capacity to secrete enzymes. The lack of efficient genome engineering approaches and absence of robust constitutive gene expression systems limits exploitation of this organism in some protein production applications. Here we report engineering of T. reesei for high-level production of highly enriched lipase B of Candida antarctica (calB) using glucose as a carbon source. Multiplexed CRISPR/Cas9 in combination with the use of our recently established synthetic expression system (SES) enabled accelerated construction of strains, which produced high amounts of highly pure calB. Using SES, calB production levels in cellulase-inducing medium were comparable to the levels obtained by using the commonly employed inducible cbh1 promoter, where a wide spectrum of native enzymes were co-produced. Due to highly constitutive expression provided by the SES, it was possible to carry out the production in cellulase-repressing glucose medium leading to around 4 grams per liter of fully functional calB and simultaneous elimination of unwanted background enzymes.

Biocompatibility of injectable resilin-based hydrogels

Vocal folds are connective tissues housed in the larynx, which can be subjected to various injuries and traumatic stimuli that lead to aberrant tissue structural alterations and fibrotic-induced biomechanical stiffening observed in patients with voice disorders. Much effort has been devoted to generate soft biomaterials that are injectable directly to sites of injury. To date, materials applied toward these applications have been largely focused on natural extracellular matrix-derived materials such as collagen, fibrin or hyaluronic acid; these approaches have suffered from the fact that materials are not sufficiently robust mechanically nor offer sufficient flexibility to modulate material properties for targeted injection. We have recently developed multiple resilin-inspired elastomeric hydrogels that possess similar mechanical properties as those reported for vocal fold tissues, and that also show promising in vitro cytocompatibility and in vivo biocompatibility. Here we report studies that test the delivery of resilin-based hydrogels through injection to the subcutaneous tissue in a wild-type mice model; histological and genetic expression outcomes were monitored. The rapid kinetics of crosslinking enabled facile injection and ensured the rapid transition of the viscous resilin precursor solution to a solid-like hydrogel in the subcutaneous space in vivo; the materials exhibited storage shear moduli in the range of 1000-2000 Pa when characterized through oscillatory rheology. Histological staining and gene expression profiles suggested minimal inflammatory profiles three weeks after injection, thereby demonstrating the potential suitability for site-specific in vivo injection of these elastomeric materials. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2229-2242, 2018.

Coacervation of resilin fusion proteins containing terminal functionalities

Liquid-liquid phase transition known as coacervation of resilin-like-peptide fusion proteins containing different terminal domains were investigated. Two different modular proteins were designed and produced and their behavior were compared to a resilin-like-peptide without terminal domains. The size of the particle-like coacervates was modulated by the protein concentration, pH and temperature. The morphology and three-dimensional (3D) structural details of the coacervate particles were investigated by cryogenic transmission electron microscopy (cryo-TEM) and tomography (cryo-ET) reconstruction. Selective adhesion of the coacervates on cellulose and graphene surfaces was demonstrated.

Advanced Materials through Assembly of Nanocelluloses

There is an emerging quest for lightweight materials with excellent mechanical properties and economic production, while still being sustainable and functionalizable. They could form the basis of the future bioeconomy for energy and material efficiency. Cellulose has long been recognized as an abundant polymer. Modified celluloses were, in fact, among the first polymers used in technical applications; however, they were later replaced by petroleum-based synthetic polymers. Currently, there is a resurgence of interest to utilize renewable resources, where cellulose is foreseen to make again a major impact, this time in the development of advanced materials. This is because of its availability and properties, as well as economic and sustainable production. Among cellulose-based structures, cellulose nanofibrils and nanocrystals display nanoscale lateral dimensions and lengths ranging from nanometers to micrometers. Their excellent mechanical properties are, in part, due to their crystalline assembly via hydrogen bonds. Owing to their abundant surface hydroxyl groups, they can be easily modified with nanoparticles, (bio)polymers, inorganics, or nanocarbons to form functional fibers, films, bulk matter, and porous aerogels and foams. Here, some of the recent progress in the development of advanced materials within this rapidly growing field is reviewed.