A Sustainable Biomineralization Approach for the Synthesis of Highly Fluorescent Ultra-Small Pt Nanoclusters.

Herein we report the first example of a facile biomineralization process to produce ultra-small-sized highly fluorescent aqueous dispersions of platinum noble metal quantum clusters (Pt-NMQCs) using a multi-stimulus responsive, biomimetic intrinsically disordered protein (IDP), Rec1-resilin. We demonstrate that Rec1-resilin acts concurrently as the host, reducing agent, and stabilizer of the blue-green fluorescent Pt-NMQCs once they are being formed. The photophysical properties, quantum yield, and fluorescence lifetime measurements of the synthesized Pt-NMQCs were examined using UV-Vis and fluorescence spectroscopy. The oxidation state of the Pt-NMQCs was quantitatively analyzed using X-ray photoelectron spectroscopy. Both a small angle X-ray scattering technique and a modeling approach have been attempted to present a detailed understanding of the structure and conformational dynamics of Rec1-resilin as an IDP during the formation of the Pt-NMQCs. It has been demonstrated that the green fluorescent Pt-NMQCs exhibit a high quantum yield of ~7.0% and a lifetime of ~9.5 ns in aqueous media. The change in photoluminescence properties due to the inter-dot interactions between proximal dots and aggregation of the Pt-NMQCs by evaporation was also measured spectroscopically and discussed.

Agrocin 108 is a 5'-cytidine nucleotide bacteriocin containing a carbocyclic phosphoryl-ascorbate group.

Agrocin 108 is a 3'-O-ß-D-xylopyranosyl-cytidine-5'-O-phosphodiester of an ascorbate-carbocyclic cyclopentenone analogue, with bacteriocin-like properties. This bacteriocin exhibits orders of magnitude greater than the inhibition zone diameter towards the indicator strain than either ampicillin or streptomycin. It has been isolated from cultures of Rhizobium rhizogenes strain K108. The structure of the agrocin 108 without detail, has been previously published. We now report a detailed structure elucidation, including the hitherto undetermined residual 5'-phospho-diester fragment by a combination of 1D and 2D NMR studies at various pH values in H2O/D2O, high resolution MS, pKa determination, and chemical degradation.

Effects of Crowding and Environment on the Evolution of Conformational Ensembles of the Multi-Stimuli-Responsive Intrinsically Disordered Protein, Rec1-Resilin: A Small-Angle Scattering Investigation.

In this study, we explore the overall structural ensembles and transitions of a biomimetic, multi-stimuli-responsive, intrinsically disordered protein (IDP), Rec1-resilin. The structural transition of Rec1-resilin with change in molecular crowding and environment is evaluated using small-angle neutron scattering and small-angle X-ray scattering. The quantitative analyses of the experimental scattering data using a combination of computational models allowed comprehensive description of the structural evolution, organization, and conformational ensembles of Rec1-resilin in response to the changes in concentration, pH, and temperature. Rec1-resilin in uncrowded solutions demonstrates the equilibrium intrinsic structure quality of an IDP with radius of gyration Rg ∼ 5 nm, and a scattering function for the triaxial ellipsoidal model best fit the experimental dataset. On crowding (increase in concentration >10 wt %), Rec1-resilin molecules exert intermolecular repulsive force of interaction, the Rg value reduces with a progressive increase in concentration, and molecular chains transform from a Gaussian coil to a fully swollen coil. It is also revealed that the structural organization of Rec1-resilin dynamically transforms from a rod (pH 2) to coil (pH 4.8) and to globular (pH 12) as a function of pH. The findings further support the temperature-triggered dual-phase-transition behavior of Rec1-resilin, exhibiting rod-shaped structural organization below the upper critical solution temperature (∼4 °C) and a large but compact structure above the lower critical solution temperature (∼75 °C). This work attempted to correlate unusual responsiveness of Rec1-resilin to the evolution of conformational ensembles.

Structural ensembles reveal intrinsic disorder for the multi-stimuli responsive bio-mimetic protein Rec1-resilin.

Rec1-resilin is the first recombinant resilin-mimetic protein polymer, synthesized from exon-1 of the Drosophila melanogaster gene CG15920 that has demonstrated unusual multi-stimuli responsiveness in aqueous solution. Crosslinked hydrogels of Rec1-resilin have also displayed remarkable mechanical properties including near-perfect rubber-like elasticity. The structural basis of these extraordinary properties is not clearly understood. Here we combine a computational and experimental investigation to examine structural ensembles of Rec1-resilin in aqueous solution. The structure of Rec1-resilin in aqueous solutions is investigated experimentally using circular dichroism (CD) spectroscopy and small angle X-ray scattering (SAXS). Both bench-top and synchrotron SAXS are employed to extract structural data sets of Rec1-resilin and to confirm their validity. Computational approaches have been applied to these experimental data sets in order to extract quantitative information about structural ensembles including radius of gyration, pair-distance distribution function, and the fractal dimension. The present work confirms that Rec1-resilin is an intrinsically disordered protein (IDP) that displays equilibrium structural qualities between those of a structured globular protein and a denatured protein. The ensemble optimization method (EOM) analysis reveals a single conformational population with partial compactness. This work provides new insight into the structural ensembles of Rec1-resilin in solution.

A multi-responsive intrinsically disordered protein (IDP)-directed green synthesis of fluorescent gold nanoclusters.

Herein we demonstrate the green synthesis of fluorescent gold nanoclusters (AuNCs) using a multi-responsive intrinsically disordered protein (IDP) polymer, Rec1-resilin, as a multi-functional template. In a controlled environment, Rec1-resilin acts simultaneously as the directing agent and the reducer, and performs the role of a highly efficient stabilizer once AuNCs are formed. The evolution of the photophysical properties and the chemical states of AuNCs formed are measured using UV-Vis, fluorescence and X-ray photoelectron spectroscopy. Circular dichroism (CD) spectroscopy measures the intrinsically disordered nature of Rec1-resilin stabilizing AuNCs. High resolution transmission electron microscopy (HR-TEM) reveals the detailed structure and morphology of the generated AuNCs of <1.5 nm size. A local ordering resembling that of a face-centered cubic (FCC) structure with evidence of twinning was observed for the generated AuNCs. The AuNCs so formed exclude the use of toxic reducing agents and display excellent water dispersibility, photostability and environmental stability towards aggregation.

An16-resilin: an advanced multi-stimuli-responsive resilin-mimetic protein polymer.

Engineered protein polymers that display responsiveness to multiple stimuli are emerging as a promising class of soft material with unprecedented functionality. The remarkable advancement in genetic engineering and biosynthesis has created the opportunity for precise control over the amino acid sequence, size, structure and resulting functions of such biomimetic proteins. Herein, we describe the multi-stimuli-responsive characteristics of a resilin-mimetic protein, An16-resilin (An16), derived from the consensus sequence of resilin gene in the mosquito Anopheles gambiae. We demonstrate that An16 is an intrinsically disordered protein that displays unusual dual-phase thermal transition behavior along with responsiveness to pH, ion, light and humidity. Identifying the molecular mechanisms that allow An16 to sense and switch in response to varying environments furthers the ability to design intelligent biomacromolecules.

Identification of proteins associated with adhesive prints from Holothuria dofleinii Cuvierian tubules.

Cuvierian tubules are expelled as a defence mechanism against predators by various species within the family Holothuridae. When the tubules are expelled, they become sticky almost immediately and ensnare the predator. The mechanism of this rapid adhesion is not clear, but proteins on the surface of the expelled tubules are widely believed to be involved. This study has examined such proteins from Holothuria dofleinii, sourced from adhesive prints left on glass after the removal of adhered tubules. Gel electrophoresis showed that seven strongly staining protein bands were consistently present in all samples, with molecular masses ranging from 89 to 17 kDa. N-terminal sequence data was obtained from two bands, while others seemed blocked. Tandem mass spectrometry-based sequencing of tryptic peptides derived from individual protein bands indicated that the proteins were unlikely to be homopolymers. PCR primers designed using the peptide sequences enabled us to amplify, clone and sequence cDNA segments relating to four gel bands; for each, the predicted translation product contained other peptide sequences observed for that band that had not been used in primer design. Database searches using the peptide and cDNA-encoded sequences suggest that two of the seven proteins are novel and one is a C-type lectin, while-surprisingly-at least three of the other four are closely related to enzymes associated with the pentose phosphate cycle and glycolysis. We discuss precedents in which lectins and metabolic enzymes are involved in attachment and adhesion phenomena.

Multi-responsive biomaterials and nanobioconjugates from resilin-like protein polymers.

Nature, through evolution over millions of years, has perfected materials with amazing characteristics and awe-inspiring functionalities that exceed the performance of man-made synthetic materials. One such remarkable material is native resilin - an extracellular skeletal protein that plays a major role in the jumping, flying, and sound production mechanisms in many insects. It is one of the most resilient (energy efficient) elastomeric biomaterials known with a resilience of ∼97% and a fatigue life in excess of 300 million cycles. Recently, resilin-like polypeptides (RLPs) with exquisite control over the amino acid sequence (comprising repeat resilin motifs) and tuneable biological properties and/or functions have been generated by genetic engineering and cloning techniques. RLPs have been the subject of intensive investigation over a decade and are now recognized to be multi-functional and multi-stimuli responsive; including temperature (exhibiting both an upper and a lower critical solution temperature), pH, moisture, ion and photo-responsive with tuneable photo-physical properties. Such unusual multi-stimuli responsiveness has scarcely been offered and reported for either synthetic or natural biopolymers. Furthermore, the directed molecular self-assembly property of RLPs also exhibits promise as efficient templates for the synthesis and stabilization of metal nanoparticles. These developments and observations reveal the opportunities and new challenges for RLPs as novel materials for nanotechnology, nanobiotechnology and therapeutic applications. In this review, we discuss and highlight the design and synthesis of different RLPs, their unique molecular architecture, advanced responsive behaviour, and functionality of hydrogels, solid-liquid interfaces, nanoparticles and nanobioconjugates derived from RLPs.

Controlled surface modification of tissue culture polystyrene for selective cell binding using resilin-inspired polypeptides.

Modified tissue culture polystyrene (TCP) surfaces have been fabricated by attachment of recombinant polypeptides based on Drosophila melanogaster resilin and the Anopheles gambiae resilin-like protein. The D. melanogaster polypeptide (Rec-1) was from the first exon of resilin and consisted of 17 very similar repeats of a 15 residue sequence. The A. gambiae polypeptide consisted of 16 repeats of an 11 residue consensus sequence (An16). Polypeptides were attached to the TCP surface through tyrosine-based photo-crosslinking using blue light in combination with (RuII(bpy)3)Cl2 and sodium persulfate. TCP that has been manufactured by mild oxidation has surface phenolic groups that are believed to participate in this crosslinking process. X-ray photoelectron spectroscopy and contact angle analyses were used to demonstrate polypeptide binding. At higher coating concentrations of Rec-1 and An16, the surface was passivated and fibroblasts no longer attached and spread. At coating concentrations of 1 mg ml(-1) for Rec-1 and 0.1 mg ml(-1) for An16, where the surface was fully passivated against fibroblast attachment, addition of a cell attachment peptide, cyclo(Arg-Gly-Asp-D-Tyr-Lys) during coating and photo-crosslinking at >0.1 mg ml(-1), led to the restoration of fibroblast binding that was dependent on the integrin αV chain.

Purification of recombinant protein by cold-coacervation of fusion constructs incorporating resilin-inspired polypeptides.

Polypeptides containing between 4 and 32 repeats of a resilin-inspired sequence AQTPSSYGAP, derived from the mosquito Anopheles gambiae, have been used as tags on recombinant fusion proteins. These repeating polypeptides were inspired by the repeating structures that are found in resilins and sequence-related proteins from various insects. Unexpectedly, an aqueous solution of a recombinant resilin protein displays an upper critical solution temperature (cold-coacervation) when held on ice, leading to a separation into a protein rich phase, typically exceeding 200 mg/mL, and a protein-poor phase. We show that purification of recombinant proteins by cold-coacervation can be performed when engineered as a fusion partner to a resilin-inspired repeat sequence. In this study, we demonstrate the process by the recombinant expression and purification of enhanced Green fluorescent protein (EGFP) in E. coli. This facile purification system can produce high purity, concentrated protein solutions without the need for affinity chromatography or other time-consuming or expensive purification steps, and that it can be used with other bulk purification steps such as low concentration ammonium sulfate precipitation. Protein purification by cold-coacervation also minimizes the exposure of the target protein to enhanced proteolysis at higher temperature.

Stabilization of collagen tissues by photocrosslinking.

Photocrosslinking, using 2 mM Ru(II)(bpy)(3)Cl(2) and various concentrations of sodium persulfate with irradiation by blue light, ∼455 nm, has been shown to be a rapid and effective method for crosslinking various tissues: tendon, amnion membrane, pericardium, and heart valve leaflet. The presence of new crosslinking was demonstrated by the increase in the shrinkage temperature of these tissues. In all the cases, increase in the shrinkage temperatures were seen, although at higher sodium persulfate concentrations, for example, 100 mM, both with and without the Ru(II)(bpy)(3)Cl(2) catalyst, some degradation of the collagenous tissues was found. The effectiveness of this photocrosslinking method when used with tissues was also shown through the increase in the break strength of tissues after crosslinking, and by the reduction of protein that could be extracted by urea. In solution studies, dityrosine has been shown to be formed during photocrosslinking. With tissues, Western blotting showed the presence of new dityrosine crosslinked proteins.

Expression of the rubber-like protein, resilin, in developing and functional insect cuticle determined using a Drosophila anti-Rec 1 resilin antibody.

BACKGROUND: The natural elastomeric protein, insect resilin, is the most efficient elastic material known, used to store energy for jumping and flight in a variety of insects. Here, an antibody to recombinant Drosophila melanogaster pro-resilin is used to examine resilin expression in Drosophila and a wider range of insects. RESULTS: Immunostaining of Drosophila embryos reveals anti-resilin reactivity in epidermal patches that exhibit a dynamic spatial and temporal expression through late embryogenesis. Resilin is also detected in stretch receptors in the embryo. In developing adult Drosophila, resilin pads are described at the base of wings and at the base of flexible sensory hairs in pupae. Resilin is also detected in embryos of the tephritid fruitfly, Bactrocera tryoni, and two well-known concentrations of insect resilin: the flight muscle tendon of the dragonfly and the pleural arch of the flea. CONCLUSIONS: The anti-Rec1 antibody antibody developed using Drosophila pro-resilin as antigen is cross-reactive and is useful for detection of resilin in diverse insects. For the first time, resilin expression has been detected during embryogenesis, revealing segmental patches of resilin in the developing epidermis of Drosophila.

A highly elastic and adhesive gelatin tissue sealant for gastrointestinal surgery and colon anastomosis.

BACKGROUND: We describe the development of a highly elastic and adhesive surgical tissue sealant, based on photochemically crosslinked gelatin, for sealing sutured incisions in the gastrointestinal (GI) tract in a rabbit surgical model and in a canine colon anastomosis study. METHODS: The study included in vitro assessment of mechanical parameters of the tissue sealant and in vivo analysis of burst strength and histology at 24 h, 3 days and 7 days post surgery, in a rabbit model, to assess progress of wound healing at the suture sites. Utility of this sealant to repair and seal a lower colonic resection and anastomosis procedure in a canine model was also investigated. RESULTS: We show that a photopolymerised gelatin tissue sealant provides effective sealing of GI incisions and facilitates wound healing with no evidence of inflammation up to 28 days post-surgery. Blending of derivatised gelatin with underivatised gelatin allowed tuning of elasticity and elastic modulus of the photopolymerised sealant to suit surgical applications. High tissue adhesive strength was maintained at all blend ratios and exceeded 100 kPa. CONCLUSIONS: This highly elastic and adhesive photopolymerised gelatin tissue sealant offers a number of advantages over currently available sealants suitable for GI surgical procedures.

Antibody labelling of resilin in energy stores for jumping in plant sucking insects.

The rubbery protein resilin appears to form an integral part of the energy storage structures that enable many insects to jump by using a catapult mechanism. In plant sucking bugs that jump (Hemiptera, Auchenorrhyncha), the energy generated by the slow contractions of huge thoracic jumping muscles is stored by bending composite bow-shaped parts of the internal thoracic skeleton. Sudden recoil of these bows powers the rapid and simultaneous movements of both hind legs that in turn propel a jump. Until now, identification of resilin at these storage sites has depended exclusively upon characteristics that may not be specific: its fluorescence when illuminated with specific wavelengths of ultraviolet (UV) light and extinction of that fluorescence at low pH. To consolidate identification we have labelled the cuticular structures involved with an antibody raised against a product of the Drosophila CG15920 gene. This encodes pro-resilin, the first exon of which was expressed in E. coli and used to raise the antibody. We show that in frozen sections from two species, the antibody labels precisely those parts of the metathoracic energy stores that fluoresce under UV illumination. The presence of resilin in these insects is thus now further supported by a molecular criterion that is immunohistochemically specific.

Molecular and functional characterisation of resilin across three insect orders.

Resilin is an important elastomeric protein of insects, with roles in the storage and release of energy during a variety of different functional categories including flight and jumping. To date, resilin genes and protein function have been characterised only in a small number of flying insects, despite their importance in fleas and other jumping insects. Microscopy and immunostaining studies of resilin in flea demonstrate the presence of resilin pads in the pleural arch at the top of the hind legs, a region responsible for the flea's jumping ability. A degenerate primer approach was used to amplify resilin gene transcripts from total RNA isolated from flea (Ctenocephalides felis), buffalo fly (Haematobia irritans exigua) and dragonfly (Aeshna sp.) pharate adults, and full-length transcripts were successfully isolated. Two isoforms (A and B) were amplified from each of flea and buffalo fly, and isoform B only in dragonfly. Flea and buffalo fly isoform B transcripts were expressed in an Escherichia coli expression system, yielding soluble recombinant proteins Cf-resB and Hi-resB respectively. Protein structure and mechanical properties of each protein before and after crosslinking were assessed. This study shows that resilin gene and protein sequences are broadly conserved and that crosslinked recombinant resilin proteins share similar mechanical properties from flying to jumping insects. A combined use of degenerate primers and polyclonal sera will likely facilitate characterisation of resilin genes from other insect and invertebrate orders.

The effect of hydration on molecular chain mobility and the viscoelastic behavior of resilin-mimetic protein-based hydrogels.

The outstanding rubber-like elasticity of resilin and resilin-mimetic proteins depends critically on the level of hydration. In this investigation, water vapor sorption and the role of hydration on the molecular chain dynamics and viscoelastic properties of resilin-mimetic protein, rec1-resilin is investigated in detail. The dynamic and equilibrium swelling behavior of the crosslinked protein hydrogels with different crosslink density are reported under various controlled environments. We propose three different stages of hydration; involving non-crystallizable water, followed by condensation or clustering of water around the already hydrated sites, and finally crystallizable water. The kinetics of water sorption for this engineering protein is observed to be comparable to hydrophilic polymers with a diffusion coefficient in the range of 10(-7) cm(2) s(-1). From the comparison between the absorption and desorption isotherms at a constant water activity, it has been observed that rec1-resilin exhibits sorption hysteresis only for the tightly bound water. Investigation of molecular mobility using differential scanning calorimetry, indicates that dehydrated crosslinked rec1-resilin is brittle with a glass transition temperature (T(g)) of >180 °C, which dramatically decreases with increasing hydration; and above a critical level of hydration rec1-resilin exhibits rubber-like elasticity. Nanoindentation studies show that even with little hydration (<10%), the mechanical properties of rec1-resilin gels change dramatically. Rheological investigations confirm that the equilibrium-swollen crosslinked rec1-resilin hydrogel exhibits outstanding elasticity and resilience of ∼ 92%, which exceeds that of any other synthetic polymer and biopolymer hydrogels.

Self-organization, interfacial interaction and photophysical properties of gold nanoparticle complexes derived from resilin-mimetic fluorescent protein rec1-resilin.

In this investigation we report the synthesis of optically coupled hybrid architectures based on a new biomimetic fluorescent protein rec1-resilin and nanometer-scale gold nanoparticles (AuNPs) in a one-step method using a non-covalent mode of binding protocol. The presence of uniformly distributed fluorophore sequences, -Ser(Thr)-Tyr-Gly- along the molecular structure of rec1-resilin provides significant opportunity to synthesize fluorophore-modified AuNPs bioconjugates with unique photophysical properties. The detailed analyses of the AuNP-bioconjugates, synthesized under different experimental conditions using spectroscopic, microscopic and scattering techniques demonstrate the organizational pathways and the electronic and photophysical properties of the developed AuNP-rec1-resilin bioconjugates. The calculation of the bimolecular quenching constant using the Stern-Volmer equation confirms that the dominant mechanism involved in quenching of fluorescence of rec1-resilin in the presence of AuNP is static. Photoacoustic infrared spectroscopy was employed to understand the nature of the interfacial interaction between the AuNP and rec1-resilin and its evolution with pH. In such bioconjugates the quenched emission of fluorescence by AuNP on the fluorophore moiety of rec1-resilin in the immediate vicinity of the AuNP has significant potential for fluorescence-based detection schemes, sensors and also can be incorporated into nanoparticle-based devices.

Photochemically crosslinked matrices of gelatin and fibrinogen promote rapid cell proliferation.

Here we report the use of a facile photochemical crosslinking method to fabricate stable polymer matrices from unmodified gelatin and fibrinogen. Gels were produced by covalent crosslinking of the proteins in a rapid photo-oxidative process, catalysed by a ruthenium metal complex and irradiation with visible light. For generation of macroporous, spongy matrices, the proteins and crosslinking reagents were mixed with catalase and hydrogen peroxide to achieve a foaming reaction, producing a stable, foamed matrix that was subsequently photo-crosslinked. C2C12 cells were either seeded onto the matrices after photo-curing or embedded in the protein matrix prior to foaming and crosslinking. Cells seeded onto scaffolds post-curing showed high cell viability and rapid proliferation in vitro. For cells embedded in the matrix prior to crosslinking there was some loss of initial viability, but surviving cells were able to proliferate after a period of in vitro cultivation. The matrices were shown to be biocompatible when implanted into nude mice, with evidence of proliferation and differentiation of cells seeded into the scaffolds. The results are promising for further development of tissue-engineering scaffolds based on this ruthenium-catalysed photo-crosslinking method.

Photochemical crosslinking of soluble wool keratins produces a mechanically stable biomaterial that supports cell adhesion and proliferation.

Keratins extracted from various "hard tissues" such as wool, hair, and nails are increasingly being investigated as a source of abundant, biocompatible materials. In this study we explored a recent photochemical method to crosslink solubilized wool keratoses, with the aim of producing a mechanically favorable biomaterial. Wool proteins were isolated by oxidizing the disulfides and extracting the resulting soluble keratoses. The α- and γ-keratose fractions were analyzed by liquid chromatography-mass spectrometry to identify their constituent proteins. Hydrogels were produced by covalent crosslinking of the α-keratoses via a photo-oxidative process catalyzed by blue light, a ruthenium complex, and persulfate. The presence of dityrosine crosslinks was demonstrated by high performance liquid chromatography and mass spectrometry analyses. The crosslinked α-keratose material had moderate tensile strength and elasticity, and high adhesive strength. The material displayed modest shrinking after crosslinking, however the shrinking could be prevented by crosslinking in the presence of 2.5% glycerol, resulting in gels that did not shrink or swell. Small solutes such as Tris and glycerol influenced the crosslink density and elastic modulus of the crosslinked material. The α-keratose was able to support adhesion and growth of NIH/3T3 fibroblasts in vitro. The fabrication of mechanically stable keratin biomaterials by this facile photo-crosslinking method may be useful for various tissue engineering applications.