Fusion order controls expression level and activity of elastin-like polypeptide fusion proteins

Genetic Functionalization of Protein-Based Biomaterials via Protein Fusions

Proteins implement many useful functions, including binding ligands with unparalleled affinity and specificity, catalyzing stereospecific chemical reactions, and directing cell behavior. Incorporating proteins into materials has the potential to imbue devices with these desirable traits. This review highlights recent advances in creating active materials by genetically fusing a self-assembling protein to a functional protein. These fusion proteins form materials while retaining the function of interest. Key advantages of this approach include elimination of a separate functionalization step during materials synthesis, uniform and dense coverage of the material by the functional protein, and stabilization of the functional protein. This review focuses on macroscale materials and discusses (i) multiple strategies for successful protein fusion design, (ii) successes and limitations of the protein fusion approach, (iii) engineering solutions to bypass any limitations, (iv) applications of protein fusion materials, including tissue engineering, drug delivery, enzyme immobilization, electronics, and biosensing, and (v) opportunities to further develop this useful technique.

Understanding the Phase Behavior of a Multistimuli-Responsive Elastin-like Polymer: Insights from Dynamic Light Scattering Analysis

Elastin-like polymers are a class of stimuli-responsive protein polymers that hold immense promise in applications such as drug delivery, hydrogels, and biosensors. Yet, understanding the intricate interplay of factors influencing their stimuli-responsive behavior remains a challenging frontier. Using temperature-controlled dynamic light scattering and zeta potential measurements, we investigate the interactions between buffer, pH, salt, water, and protein using an elastin-like polymer containing ionizable lysine residues. We observed the elevation of transition temperature in the presence of the common buffering agent HEPES at low concentrations, suggesting a "salting-in" effect of HEPES as a cosolute through weak association with the protein. Our findings motivate a more comprehensive investigation of the influence of buffer and other cosolute molecules on elastin-like polymer behavior.

Isolation of nucleic acids using liquid-liquid phase separation of pH-sensitive elastin-like polypeptides

Extraction of nucleic acids (NAs) is critical for many methods in molecular biology and bioanalytical chemistry. NA extraction has been extensively studied and optimized for a wide range of applications and its importance to society has significantly increased. The COVID-19 pandemic highlighted the importance of early and efficient NA testing, for which NA extraction is a critical analytical step prior to the detection by methods like polymerase chain reaction. This study explores simple, new approaches to extraction using engineered smart nanomaterials, namely NA-binding, intrinsically disordered proteins (IDPs), that undergo triggered liquid-liquid phase separation (LLPS). Two types of NA-binding IDPs are studied, both based on genetically engineered elastin-like polypeptides (ELPs), model IDPs that exhibit a lower critical solution temperature in water and can be designed to exhibit LLPS at desired temperatures in a variety of biological solutions. We show that ELP fusion proteins with natural NA-binding domains can be used to extract DNA and RNA from physiologically relevant solutions. We further show that LLPS of pH responsive ELPs that incorporate histidine in their sequences can be used for both binding, extraction and release of NAs from biological solutions, and can be used to detect SARS-CoV-2 RNA in samples from COVID-positive patients.

Therapeutic Peptides, Proteins and their Nanostructures for Drug Delivery and Precision Medicine

Peptide and protein nanostructures with tunable structural features, multifunctionality, biocompatibility and biomolecular recognition capacity enable development of efficient targeted drug delivery tools for precision medicine applications. In this review article, we present various techniques employed for the synthesis and self-assembly of peptides and proteins into nanostructures. We discuss design strategies utilized to enhance their stability, drug-loading capacity, and controlled release properties, in addition to the mechanisms by which peptide nanostructures interact with target cells, including receptor-mediated endocytosis and cell-penetrating capabilities. We also explore the potential of peptide and protein nanostructures for precision medicine, focusing on applications in personalized therapies and disease-specific targeting for diagnostics and therapeutics in diseases such as cancer.

Vascular Endothelial Growth Factor Receptor 1 Targeting Fusion Polypeptides with Stimuli-Responsiveness for Anti-angiogenesis

Genetically engineered fusion polypeptides have been investigated to introduce unique bio-functionality and improve some therapeutic activity for anti-angiogenesis. We report herein that stimuli-responsive, vascular endothelial growth factor receptor 1 (VEGFR1) targeting fusion polypeptides composed of a VEGFR1 (fms-like tyrosine kinase-1 (Flt1)) antagonist, an anti-Flt1 peptide, and a thermally responsive elastin-based polypeptide (EBP) were rationally designed at the genetic level, biosynthesized, and purified by inverse transition cycling to develop potential anti-angiogenic fusion polypeptides to treat neovascular diseases. A series of hydrophilic EBPs with different block lengths were fused with an anti-Flt1 peptide, forming anti-Flt1-EBPs, and the effect of EBP block length on their physicochemical properties was examined. While the anti-Flt1 peptide decreased phase-transition temperatures of anti-Flt1-EBPs, compared with EBP blocks, anti-Flt1-EBPs were soluble under physiological conditions. The anti-Flt1-EBPs dose dependently inhibited the binding of VEGFR1 against vascular endothelial growth factor (VEGF) as well as tube-like network formation of human umbilical vein endothelial cells under VEGF-triggered angiogenesis in vitro because of the specific binding between anti-Flt1-EBPs and VEGFR1. Furthermore, the anti-Flt1-EBPs suppressed laser-induced choroidal neovascularization in a wet age-related macular degeneration mouse model in vivo. Our results indicate that anti-Flt1-EBPs as VEGFR1-targeting fusion polypeptides have great potential for efficacious anti-angiogenesis to treat retinal-, corneal-, and choroidal neovascularization.

Engineering synthetic biomolecular condensates

The concept of phase-separation-mediated formation of biomolecular condensates provides a new framework to understand cellular organization and cooperativity-dependent cellular functions. With growing understanding of how biological systems drive phase separation and how cellular functions are encoded by biomolecular condensates, opportunities have emerged for cellular control through engineering of synthetic biomolecular condensates. In this Review, we discuss how to construct synthetic biomolecular condensates and how they can regulate cellular functions. We first describe the fundamental principles by which biomolecular components can drive phase separation. Next, we discuss the relationship between the properties of condensates and their cellular functions, which informs the design of components to create programmable synthetic condensates. Finally, we describe recent applications of synthetic biomolecular condensates for cellular control and discuss some of the design considerations and prospective applications.

A guide to designing photocontrol in proteins: methods, strategies and applications

Light is essential for various biochemical processes in all domains of life. In its presence certain proteins inside a cell are excited, which either stimulates or inhibits subsequent cellular processes. The artificial photocontrol of specifically proteins is of growing interest for the investigation of scientific questions on the organismal, cellular and molecular level as well as for the development of medicinal drugs or biocatalytic tools. For the targeted design of photocontrol in proteins, three major methods have been developed over the last decades, which employ either chemical engineering of small-molecule photosensitive effectors (photopharmacology), incorporation of photoactive non-canonical amino acids by genetic code expansion (photoxenoprotein engineering), or fusion with photoreactive biological modules (hybrid protein optogenetics). This review compares the different methods as well as their strategies and current applications for the light-regulation of proteins and provides background information useful for the implementation of each technique.

Improving biocatalytic properties of an azoreductase via the N-terminal fusion of formate dehydrogenase

Azoreductases require NAD(P)H to reduce azo dyes but the costly price of NAD(P)H limits its application. Formate dehydrogenase (FDH) allows NAD(P)+ recycling and therefore, the fusion of these two biocatalysts seems promising. This study investigated the changes to the fusion protein involving azoreductase (AzoRo) of Rhodococcus opacus 1CP and FDH (FDHC23S and FDHC23SD195QY196H) of Candida boidinii in different positions with His-tag as the linker. The position affected enzyme activities as AzoRo activity decreased by 20-fold when it is in the N-terminus of the fusion protein. FDHC23S+AzoRo was the most active construct and was further characterized. Enzymatic activities of FDHC23S+AzoRo decreased compared to parental enzymes but showed improved substrate scope - accepting bulkier dyes. Moreover, pH has an influence on the stability and activity of the fusion protein because at pH 6 (pH that is suboptimal for FDH), the dye reduction decreased to more than 50% and this could be attributed to the impaired NADH supply for the AzoRo part.

Anti-CD99 scFv-ELP nanoworms for the treatment of acute myeloid leukemia

CD99 is a transmembrane glycoprotein shown to be upregulated in various malignancies. We have previously reported CD99 to be highly upregulated and present a viable therapeutic target in acute myeloid leukemia (AML). Currently, no therapy against CD99 is under clinical investigation. As a surface molecule, CD99 can be targeted with an antibody-based approach. Here, we have developed a new modality to target CD99 by engineering a fusion protein composed of a single-chain variable fragment antibody (anti-CD99 scFv) conjugated with a high molecular weight elastin-like polypeptide (ELP), A192: α-CD99-A192. This fusion protein assembles into multi-valent nanoworm with optimal physicochemical properties and favorable pharmacokinetic parameters (half-life: 16 h). α-CD99-A192 nanoworms demonstrated excellent in vitro and in vivo anti-leukemic effects. α-CD99-A192 induced apoptotic cell death in AML cell lines and primary blasts and prolonged overall survival of AML xenograft mouse model.

Anti-FLT3 nanoparticles for acute myeloid leukemia: Preclinical pharmacology and pharmacokinetics

FLT3 receptor is an important therapeutic target in acute myeloid leukemia due to high incidence of mutations associated with poor clinical outcome. Targeted therapies against the FLT3 receptor, including small-molecule FLT3 tyrosine kinase inhibitors (TKIs) and anti-FLT3 antibodies, have demonstrated promising preclinical and even clinical efficacy. Yet, even with the current FDA approval for two FLT3 inhibitors, these modalities were unable to cure AML or significantly extend the lives of patients with a common mutation called FLT3-ITD. While FLT3 is a viable target, the approaches to inhibit its activity were inadequate. To develop a new modality for targeting FLT3, our team engineered an α-FLT3-A192 fusion protein composed of a single chain variable fragment antibody conjugated with an elastin-like polypeptide. These fusion proteins assemble into multi-valent nanoparticles with excellent stability and pharmacokinetic properties as well as in vitro and in vivo pharmacological activity in cellular and xenograft murine models of AML. In conclusion, α-FLT3-A192 fusions appear to be a viable new modality for targeting FLT3 in AML and warrant further preclinical development to bring it into the clinic.

Elastin-Like Polypeptides for Biomedical Applications

Elastin-like polypeptides (ELPs) are stimulus-responsive biopolymers derived from human elastin. Their unique properties—including lower critical solution temperature phase behavior and minimal immunogenicity—make them attractive materials for a variety of biomedical applications. ELPs also benefit from recombinant synthesis and genetically encoded design; these enable control over the molecular weight and precise incorporation of peptides and pharmacological agents into the sequence. Because their size and sequence are defined, ELPs benefit from exquisite control over their structure and function, qualities that cannot be matched by synthetic polymers. As such, ELPs have been engineered to assemble into unique architectures and display bioactive agents for a variety of applications. This review discusses the design and representative biomedical applications of ELPs, focusing primarily on their use in tissue engineering and drug delivery.

Non-chromatographic purification of thermostable endoglucanase from Thermotoga maritima by fusion with a hydrophobic elastin-like polypeptide

Endoglucanase EG12B from Thermotoga maritima is a thermophilic cellulase that has great potential for industrial applications. Here, to enable the selective purification of EG12B in a simple and efficient manner, an elastin-like polypeptide (ELP), which acts as a thermally responsive polypeptide, was fused with EG12B to enable its inverse phase transition cycling (ITC). A small gene library comprising ELPs from ELP₅ to ELP₅₀ was constructed using recursive directional ligation by plasmid reconstruction. ELP₅₀ was added to the C-terminus of EG12B as a fusion tag to obtain the expression vector pET28-EG12B-ELP₅₀, which was transformed into Escherichia coli BL21 (DE3) to enable the expression of fusion protein via IPTG induction. Gray scanning analysis revealed that the EG12B-ELP₅₀ expression level was up to about 35% of the total cellular proteins. After three rounds of ITC, 8.14 mg of EG12B-ELP₅₀ was obtained from 500-mL lysogeny broth culture medium. The recovery rate and purification fold of EG12B-ELP₅₀ purified by ITC reached 78.1% and 11.8, respectively. The cellulase activity assay showed that EG12B-ELP₅₀ had a better thermostability, higher optimal temperature, and longer half-life than those of free EG12B. Overall, our results suggested that ELP₅₀ could be used as a favorable fusion tag, providing a rapid, simple, and inexpensive strategy for non-chromatographic target-protein purification.

Functional Improvement of Human Cardiotrophin 1 Produced in Tobacco Chloroplasts by Co-expression with Plastid Thioredoxin m

Human cardiotrophin 1 (CT1), a cytokine with excellent therapeutic potential, was previously expressed in tobacco chloroplasts. However, the growth conditions required to reach the highest expression levels resulted in an impairment of its bioactivity. In the present study, we have examined new strategies to modulate the expression of this recombinant protein in chloroplasts so as to enhance its production and bioactivity. In particular, we assessed the effect of both the fusion and co-expression of Trx m with CT1 on the production of a functional CT1 by using plastid transformation. Our data revealed that the Trx m fusion strategy was useful to increase the expression levels of CT1 inside the chloroplasts, although CT1 bioactivity was significantly impaired, and this was likely due to steric hindrance between both proteins. By contrast, the expression of functional CT1 was increased when co-expressed with Trx m, because we demonstrated that recombinant CT1 was functionally active during an in vitro signaling assay. While Trx m/CT1 co-expression did not increase the amount of CT1 in young leaves, our results revealed an increase in CT1 protein stability as the leaves aged in this genotype, which also improved the recombinant protein's overall production. This strategy might be useful to produce other functional biopharmaceuticals in chloroplasts.

Incorporation of short, charged peptide tags affects the temperature responsiveness of positively-charged elastin-like polypeptides

Elastin-like polypeptides (ELPs) are recombinant protein domains exhibiting lower critical solution temperature (LCST) behavior. This LCST behavior is controlled not only by intrinsic factors including amino acid composition and polypeptide chain length but also by non-ELP fusion domains. Here, we report that the presence of a composite non-ELP sequence that includes both His and T7 tags or a short Ser-Lys-Gly-Pro-Gly (SKGPG) sequence can dramatically change the LCST behavior of a positively-charged ELP domain. Both the His and T7 tags have been widely used in recombinant protein design to enable affinity chromatography and serve as epitopes for protein detection. The SKGPG sequence has been used to improve the expression of ELPs. Both the composite tag and the SKGPG sequence are <15% of the total length of the ELP fusion proteins. Despite the small size of the composite tag, its incorporation imparted pH-sensitive LCST behavior to the positively-charged ELP fusion protein. This pH sensitivity was not observed with the incorporation of the SKGPG sequence. The pH sensitivity results from both electrostatic and hydrophobic interactions between the composite tag and the positively-charged ELP domain. The hydrophobicity of the composite tag also alters the ELP interaction with Hofmeister salts by changing the overall hydrophobicity of the fusion protein. Our results suggest that incorporation of short tag sequences should be considered when designing temperature-responsive ELPs and provide insights into utilizing both electrostatic and hydrophobic interactions to design temperature-responsive recombinant proteins as well as synthetic polymers.

Injectable Polypeptide Hydrogel Depot System for Assessment of the Immune Response-Inducing Efficacy of Sustained Antigen Release Alone

Vaccines typically contain an antigen, delivery system (vehicle), and adjuvant, all of which contribute to inducing a potent immune response. Consequently, design of new vaccines is difficult, because the contributions and interactions of these components are difficult to distinguish. Here, it is aimed to develop an easy-to-use, non-immunogenic, injectable depot system for sustained antigen release that will be suitable for assessing the efficacy of prolonged antigen exposure per se for inducing an immune response. This should mimic real-life infections. Recombinant elastin-like polypeptides with periodic cysteine residues (cELPs) are selected, which reportedly show little or no immunogenicity, as carriers and tetanus toxoid (Ttd) as an antigen. After subcutaneous injection of the mixture, cELP rapidly forms a disulfide cross-linked hydrogel in situ, within which Ttd is physically incorporated, affording a biodegradable antigen depot. A series of Ttd-containing hydrogels is examined. A single injection induces high levels of tetanus antibody with high avidity for at least 20 weeks in mice. The chain length of cELP proves critical, whereas differences in hydrophobicity has little effect, although hydrophilic cELPs are more rapidly biodegraded. This system's ability to distinguish the contribution of sustained antigen release to antibody induction should be helpful for rational design of next-generation vaccines.

Unique Phase Transition of Exogenous Fusion Elastin-like Polypeptides in the Solution Containing Polyethylene Glycol

Elastin-Like polypeptides (ELPs), as well-known temperature-controlled bio-macromolecules, are widely used. However, little is known about the interactions between ELPs and macromolecules, which is an important yet neglected problem. Here, the phase transition characteristics of an ELPs-SpyCatcher fusion protein (E-C) in the presence of polyethylene glycol (PEG) in single salts (Na2CO3, Na2SO4, NaCl) solutions were investigated using a UV spectrophotometer, DLC, and fluorescence spectroscopy, and we got some interesting results. The phases transition of E-C occurred at a concentration lower than 0.5 mol/L Na2CO3/PEG2000, while in single Na2CO3 (<0.5 mol/L), the phase transition of E-C did not occur. In the Na2CO3/PEG solution, we observed a unique two-step phase transition of E-C when the Na2CO3 concentration was 0.5 mol/L and PEG2000 concentration was less than 0.15 g/mL, respectively. In the Na2CO3/PEG2000 solution, the phase-transition temperature of E-C decreased with the increase of PEG concentration, but increased in the Na2SO4/PEG2000 solution, while it remained unchanged in the NaCl/PEG2000 solution. However, the phase-transition temperature of the linear ELPs40 decreased under the same salts/PEG2000 solutions. We also addressed the possible molecular mechanism of the interesting results. In contrast to the current well-understood salts-ELPs interactions, this work provides some new insights into the interaction between the PEG-salts-ELPs in solution.

Fusion with an albumin-binding domain improves pharmacokinetics of an αvβ3-integrin binding fibronectin scaffold protein

Fusion with an albumin-binding domain (ABD) of streptococcal protein G represents a popular approach for half-life extension of small protein therapeutics in the organism. To increase the circulation time of engineered αvβ3-integrin-binding protein (JCL) based on the 10th human fibronectin type III domain (¹⁰ Fn3), we have constructed several fusions with ABD with different orientations of the partner proteins and linker length. The recombinant proteins were expressed in Escherichia coli cells and purified by nickel-affinity chromatography. All fusion proteins bound human serum albumin (HSA) in ELISA assay; however, fusions with longer linkers demonstrated better performance. Interaction of ABD-L₁₅ -JCL and JCL-L₁₄ -ABD with HSA was confirmed by analytical size exclusion chromatography and pull-down assays. Surprisingly, the thermal stability of ABD-L₁₅ -JCL was dramatically decreased in comparison with JCL and JCL-L₁₄ -ABD proteins. Pharmacokinetic studies revealed that JCL-L₁₄ -ABD circulated in murine blood about 10 times longer than ABD-L₁₅ -JCL and 960 times longer than JCL. Biodistribution studies of JCL-L₁₄ -ABD in mice revealed its increased level in blood and a decreased accumulation in liver and kidneys in comparison with JCL. Obtained results demonstrate the utility of the fusion with ABD for half-life extension of the binding proteins based on ¹⁰ Fn3.

Trends in the design and use of elastin-like recombinamers as biomaterials

Elastin-like recombinamers (ELRs), which derive from one of the repetitive domains found in natural elastin, have been intensively studied in the last few years from several points of view. In this mini review, we discuss all the recent works related to the investigation of ELRs, starting with those that define these polypeptides as model intrinsically disordered proteins or regions (IDPs or IDRs) and its relevance for some biomedical applications. Furthermore, we summarize the current knowledge on the development of drug, vaccine and gene delivery systems based on ELRs, while also emphasizing the use of ELR-based hydrogels in tissue engineering and regenerative medicine (TERM). Finally, we show different studies that explore applications in other fields, and several examples that describe biomaterial blends in which ELRs have a key role. This review aims to give an overview of the recent advances regarding ELRs and to encourage further investigation of their properties and applications.

Engineered Ribonucleoprotein Granules Inhibit Translation in Protocells

Liquid granules rich in intrinsically disordered proteins and RNA play key roles in critical cellular functions such as RNA processing and translation. Many details of the mechanism via which this occurs remain to be elucidated. Motivated by the lacuna in the field and by the prospects of developing de novo artificial granules that provide extrinsic control of translation, we report a bottom-up approach to engineer ribonucleoprotein granules composed of a recombinant RNA-binding IDP that exhibits phase behavior in water. We developed a kinetic model to illustrate that these granules inhibit translation through reversible or irreversible sequestration of mRNA. Within monodisperse droplets capable of transcription and translation, we experimentally demonstrate temporal inhibition of translation by using designer IDPs that exhibit tunable phase behavior. This work lays the foundation for developing artificial granules that promise to further our mechanistic understanding of their naturally occurring counterparts.

Biotechnological applications of elastin-like polypeptides and the inverse transition cycle in the pharmaceutical industry

Proteins are essential throughout the biological and biomedical sciences and the purification strategies of proteins of interest have advanced over centuries. Elastin-like polypeptides (ELPs) are compound polymers that have recently been highlighted for their sharp and reversible phase transition property when heated above their lower critical solution temperature (LCST). ELPs preserve this behavior when fused to a protein, and as a result providing a simple method to isolate a recombinant ELP fusion protein from cell contaminants by taking the solution through the soluble and insoluble phase of the ELP fusion protein, a technique designated as the inverse transition cycle (ITC). ITC is considered an inexpensive and efficient way of purifying recombinant ELP fusion proteins. In addition, ELPs render recombinant fusion protein more stability and a longer clear time in blood stream, which give ELPs a lot of valuable applications in the biotechnological and pharmaceutical industry. This article reviews the modernizations of ELPs and briefly highlights on the possible use of technologies such as the automatic piston discharge (APD) centrifuges to improve the efficiency of the ITC in the pharmaceutical industry to obtain benefits.

Multifunctional elastin-like polypeptide renders β-glucosidase enzyme phase transition and high stability

BACKGROUND

In the enzymatic conversion of biomass, it becomes an important issue to efficiently and cost-effectively degrade cellulose into fermentable glucose. β-Glucosidase (Bgluc), an essential member of cellulases, plays a critical role in cellulosic biomass degradation. The difficulty in improving the stability of Bgluc has been a bottleneck in the enzyme-dependent cellulose degradation. The traditional method of protein purification, however, leads to higher production cost and a decrease in activity. To simplify and efficiently purify Bgluc with modified special properties, Bgluc-tagged ELP and His with defined phase transitions was designed to facilitate the process.

RESULTS

Here, a novel binary ELP and His tag was fused with Bgluc from termite Coptotermes formosanus to construct a Bgluc-linker-ELP-His recombinant fusion protein (BglucLEH). The recombinant plasmid Bgluc expressing a His tag (BglucH) was also constructed. The BglucLEH and BglucH were expressed in E. coli BL21 and purified using inverse transition cycling (ITC) or Ni-NTA resin. The optimum salt concentration for the ITC purification of BglucLEH was 0.5 M (NH₄)₂SO₄ and the specific activity of BglucLEH purified by ITC was 75.5 U/mg for substrate p-NPG, which was slightly higher than that of BglucLEH purified by Ni-NTA (68.2 U/mg). The recovery rate and purification fold of BglucLEH purified by ITC and Ni-NTA were 77.8%, 79.1% and 12.60, 11.60, respectively. The results indicated that purification with ITC was superior to the traditional Ni-NTA. The K _m of BglucLEH and BglucH for p-NPG was 5.27 and 5.73 mM, respectively. The K _ca t/K _m (14.79 S^-1 mM^-1) of BglucLEH was higher than that of BglucH (12.10 S^-1 mM^-1). The effects of ELP tag on the enzyme activity, secondary structure and protein stability were also studied. The results showed that ELP tag did not affect the secondary structure or enzyme activity of Bgluc. More importantly, ELP improved the protein stability in harsh conditions such as heating and exposure to denaturant.

CONCLUSION

The Bgluc-linker-ELP-His system shows wide application prospect in maintaining the activity, efficient purification and improving the stability of Bgluc. These properties of BglucLEH make it an interesting tool to reduce cost, to improve the efficiency of biocatalyst and potentially to enhance the degradation of lignocellulosic biomass.

Rapid and simple purification of elastin-like polypeptides directly from whole cells and cell lysates by organic solvent extraction

Elastin-like polypeptides (ELP) are a well-known class of proteins that are being increasingly utilized in a variety of biomedical applications, due to their beneficial physicochemical properties. A unifying feature of ELP is their demonstration of a sequence tunable inverse transition temperature (Tt) that enables purification using a simple, straightforward process called inverse transition cycling (ITC). Despite the utility of ITC, the process is inherently limited to ELP with an experimentally accessible Tt. Since the underlying basis for the ELP Tt is related to its high overall hydrophobicity, we anticipated that ELP would be excellent candidates for purification by organic extraction. We report the first method for rapidly purifying ELP directly from whole E. coli cells or clarified lysates using pure organic solvents and solvent mixtures, followed by aqueous back extraction. Our results show that small ELP and a large ELP-fusion protein can be isolated in high yield from whole cells or cell lysates with greater than 95% purity in less than 30 min and with very low levels of LPS and DNA contamination.

Enhancing purification and plasma stability of porcine interferon-α/γ by fusion to elastin-like polypeptide

The clinical use of recombinant interferons (rIFNs) is limited by higher purification cost and quick clearance from circulation. Elastin-like polypeptides (ELPs) are a novel tag for recombinant protein purification and half-life extension. In this study, we evaluated the feasibility of ELP fusion for simple purification and half-life extension of recombinant porcine IFNs (rPoIFNs). After construction of five different fusion expression vectors, we optimized the conditions for soluble protein expression and purification. SDS-PAGE analysis showed that, unlike PoIFNα-His and PoIFNγ-His, PoIFNα-ELP, ELP-PoIFNα and PoIFNαγ-ELP were expressed mainly as soluble proteins at 20 ℃. The optimal conditions for the inverse transition cycling (ITC) of three ELP fusion proteins were 2 M NaCl at 28 ℃. After two rounds of ITC, the three ELP fusion proteins were purified to more than 90% purities, which were comparable to that of affinity-purified PoIFNα-His and PoIFNγ-His. Cytopathic effect inhibition assay showed that the five rPoIFNs had potent but different antiviral activities against two different viruses on two different cell types. The plasma solubility assay showed that the three ELP-fused rPoIFNs remained as soluble proteins under the physical conditions. The plasma stability of three ELP-fused rPoIFNs was significantly improved in comparison with that of PoIFN-α. These data suggest that ELP fusion is a feasible strategy to enhance purification and plasma stability of rPoIFNs.

Production of bioactive hepcidin by recombinant DNA tagging with an elastin-like recombinamer

With the lack of new chemical antibiotics and increasing pathogen resistance to those available, new alternatives are being explored. Antimicrobial peptides (AMPs) with a broad range of effects, including antibacterial, antifungal, and antiviral actions, have emerged as one of the options. They can be produced by recombinant DNA technology, but the chromatographic methods used for peptide purification are expensive and time consuming. Here, we describe the design, production, purification and assessment of the antibacterial activity of the human peptide hepcidin, using an elastin-like recombinamer as fusion partner. The recombinant protein Hep-A200 was produced in Escherichia coli and purified by a non-chromatographic procedure, exploiting the thermal properties of the A200 elastin-like recombinamer. Recombinant Hep-A200 was found to retain antibacterial activity against Gram-positive and Gram-negative species.

Translatable High Drug Loading Drug Delivery Systems Based on Biocompatible Polymer Nanocarriers

Most nanocarriers possess low drug loading, resulting in frequently repeated administration and thereby high cost and increased side effects. Furthermore, the characteristics of nanocarrier materials, especially the drug loading capacity, plays a vital role in the drug delivery efficacy. In this review, we focus on the readily translatable polymeric drug delivery systems with high drug loading, which are comprised of biocompatible polymers such as poly(ethylene glycol), poly( N-vinylpyrrolidone), polyoxazoline, natural proteins like albumin and casein, non-natural proteins such as recombinant elastin-like polypeptides, as well as nucleic acids. At the end of this review, applications of these polymeric nanocarriers on the delivery of proteins and gene drugs are also briefly discussed.

Elastin-like polypeptides: Therapeutic applications for an emerging class of nanomedicines

Elastin-like polypeptides (ELPs) constitute a genetically engineered class of 'protein polymers' derived from human tropoelastin. They exhibit a reversible phase separation whereby samples remain soluble below a transition temperature (Tt) but form amorphous coacervates above Tt. Their phase behavior has many possible applications in purification, sensing, activation, and nanoassembly. As humanized polypeptides, they are non-immunogenic, substrates for proteolytic biodegradation, and can be decorated with pharmacologically active peptides, proteins, and small molecules. Recombinant synthesis additionally allows precise control over ELP architecture and molecular weight, resulting in protein polymers with uniform physicochemical properties suited to the design of multifunctional biologics. As such, ELPs have been employed for various uses including as anti-cancer agents, ocular drug delivery vehicles, and protein trafficking modulators. This review aims to offer the reader a catalogue of ELPs, their various applications, and potential for commercialization across a broad spectrum of fields.

Production of a polar fish antimicrobial peptide in Escherichia coli using an ELP-intein tag

An important aspect related to infectious pathogens is their exceptional adaptability in developing resistance, which leads to a perpetual challenge in the discovery of antimicrobial drugs with novel mechanisms of action. Among them, antimicrobial peptides (AMPs) stand out as promising anti-infective molecules. In order to overcome the high costs associated with isolation from natural sources or chemical synthesis of AMPs we propose the expression of Pa-MAP 2, a polyalanine AMP. Pa-MAP 2 was fused to an ELP-intein tag where the ELP (Elastin-like polypeptide) was used to promote aggregation and fast and cost-effective isolation after expression, and the intein was used to stimulate a controlled AMP release. For these, the vector pET21a was used to produce Pa-MAP 2 fused to the N-termini region of a modified Mxe GyrA intein followed by 60 repetitions of ELP. Purified Pa-MAP 2 showed a MIC of 25μM against E. coli ATCC 8739. Batch fermentation demonstrated that Pa-MAP-2 can be produced in both rich and defined media at yields 50-fold higher than reported for other AMPs produced by the ELP-intein system, and in comparable yields to expression systems with protease or chemical cleavage.

Differential secretion pathways of proteins fused to the Escherichia coli maltose binding protein (MBP) in Pichia pastoris

The Escherichia coli maltose binding protein (MBP) is an N-terminal fusion partner that was shown to enhance the secretion of some heterologous proteins from the yeast Pichia pastoris, a popular host for recombinant protein expression. The amount of increase in secretion was dependent on the identity of the cargo protein, and the fusions were proteolyzed prior to secretion, limiting its use as a purification tag. In order to overcome these obstacles, we used the MBP as C-terminal partner for several cargo peptides. While the Cargo-MBP proteins were no longer proteolyzed in between these two moieties when the MBP was in this relative position, the secretion efficiency of several fusions was lower than when MBP was located at the opposite end of the cargo protein (MBP-Cargo). Furthermore, fluorescence analysis suggested that the MBP-EGFP and EGFP-MBP proteins followed different routes within the cell. The effect of several Pichia pastoris beta-galactosidase supersecretion (bgs) strains, mutants showing enhanced secretion of select reporters, was also investigated on both MBP-EGFP and EGFP-MBP. While the secretion efficiency, proteolysis and localization of the MBP-EGFP was influenced by the modified function of Bgs13, EGFP-MBP behavior was not affected in the bgs strain. Taken together, these results indicate that the location of the MBP in a fusion affects the pathway and trans-acting factors regulating secretion in P. pastoris.

Fabricated Elastin

The mechanical stability, elasticity, inherent bioactivity, and self-assembly properties of elastin make it a highly attractive candidate for the fabrication of versatile biomaterials. The ability to engineer specific peptide sequences derived from elastin allows the precise control of these physicochemical and organizational characteristics, and further broadens the diversity of elastin-based applications. Elastin and elastin-like peptides can also be modified or blended with other natural or synthetic moieties, including peptides, proteins, polysaccharides, and polymers, to augment existing capabilities or confer additional architectural and biofunctional features to compositionally pure materials. Elastin and elastin-based composites have been subjected to diverse fabrication processes, including heating, electrospinning, wet spinning, solvent casting, freeze-drying, and cross-linking, for the manufacture of particles, fibers, gels, tubes, sheets and films. The resulting materials can be tailored to possess specific strength, elasticity, morphology, topography, porosity, wettability, surface charge, and bioactivity. This extraordinary tunability of elastin-based constructs enables their use in a range of biomedical and tissue engineering applications such as targeted drug delivery, cell encapsulation, vascular repair, nerve regeneration, wound healing, and dermal, cartilage, bone, and dental replacement.

Elastin-like polypeptide based nanoparticles: design rationale toward nanomedicine

Elastin-like polypeptides (ELPs) are characterized by a high sequence control, temperature responsiveness and biocompatibility, which make them highly interesting as smart materials for application in nanomedicine. In particular the construction of ELP-based nanoparticles has recently become a focal point of attention in materials research. This review will give an overview of the ELP-based nanoparticles that have been developed until now and their underlying design principles. First a short introduction on ELPs and their stimulus-responsive behavior will be given. This characteristic has been applied for the development of ELP-based block copolymers that can self-assemble into nanoparticles. Both the fully ELP-based as well as several ELP hybrid materials that have been reported to form nanoparticles will be discussed, which is followed by a concise description of the promising biomedical applications reported for this class of materials.

A depot-forming glucagon-like peptide-1 fusion protein reduces blood glucose for five days with a single injection

Peptide drugs are an exciting class of pharmaceuticals for the treatment of a variety of diseases; however, their short half-life dictates multiple and frequent injections causing undesirable side effects. Herein, we describe a novel peptide delivery system that seeks to combine the attractive features of prolonged circulation time with a prolonged release formulation. This system consists of glucagon-like peptide-1, a type-2 diabetes drug fused to a thermally responsive, elastin-like-polypeptide (ELP) that undergoes a soluble-insoluble phase transition between room temperature and body temperature, thereby forming an injectable depot. We synthesized a set of GLP-1-ELP fusions and verified their proteolytic stability and potency in vitro. Significantly, a single injection of depot forming GLP-1-ELP fusions reduced blood glucose levels in mice for up to 5 days, 120 times longer than an injection of the native peptide. These findings demonstrate the unique advantages of using ELPs to release peptide-ELP fusions from a depot combined with enhanced systemic circulation to create a tunable peptide delivery system.

IL-1Ra and its delivery strategies: inserting the association in perspective

Interleukin-1 receptor antagonist (IL-1Ra) is a naturally occurring anti-inflammatory antagonist of interleukin-1 family of pro-inflammatory cytokines. The broad spectrum anti-inflammatory effects of IL-1Ra have been investigated against various auto-immune diseases such as diabetes mellitus, rheumatoid arthritis. Despite of its outstanding broad spectrum anti-inflammatory effects, IL-1Ra has short biological half-life (4-6 h) and to cope with this problem, up till now, many delivery strategies have been applied either to extend the half-life and/or prolong the steady-state sustained release of IL-1Ra from its target site. Here in our present paper, we have provided an overview of all approaches attempted to prolong the duration of therapeutic effects of IL-1Ra either by fusing IL-1Ra using fusion protein technology to extend the half-life and/or development of new dosage forms using various biodegradable polymers to prolong its steady-state sustained release at the site of administration. These approaches have been characterized by their intended impact on either in vitro release characteristics and/or pharmacokinetic and pharmacodynamic parameters of IL-1Ra. We have also compared these delivery strategies with each other on the basis of bioactivity of IL-1Ra after fusion with fusion protein partner and/or encapsulation with biodegradable polymer.

Elastin-based protein polymer nanoparticles carrying drug at both corona and core suppress tumor growth in vivo

Numerous nanocarriers of small molecules depend on either non-specific physical encapsulation or direct covalent linkage. In contrast, this manuscript explores an alternative encapsulation strategy based on high-specificity avidity between a small molecule drug and its cognate protein target fused to the corona of protein polymer nanoparticles. With the new strategy, the drug associates tightly to the carrier and releases slowly, which may decrease toxicity and promote tumor accumulation via the enhanced permeability and retention effect. To test this hypothesis, the drug Rapamycin (Rapa) was selected for its potent anti-proliferative properties, which give it immunosuppressant and anti-tumor activity. Despite its potency, Rapa has low solubility, low oral bioavailability, and rapid systemic clearance, which make it an excellent candidate for nanoparticulate drug delivery. To explore this approach, genetically engineered diblock copolymers were constructed from elastin-like polypeptides (ELPs) that assemble small (<100nm) nanoparticles. ELPs are protein polymers of the sequence (Val-Pro-Gly-Xaa-Gly)n, where the identity of Xaa and n determine their assembly properties. Initially, a screening assay for model drug encapsulation in ELP nanoparticles was developed, which showed that Rose Bengal and Rapa have high non-specific encapsulation in the core of ELP nanoparticles with a sequence where Xaa=Ile or Phe. While excellent at entrapping these drugs, their release was relatively fast (2.2h half-life) compared to their intended mean residence time in the human body. Having determined that Rapa can be non-specifically entrapped in the core of ELP nanoparticles, FK506 binding protein 12 (FKBP), which is the cognate protein target of Rapa, was genetically fused to the surface of these nanoparticles (FSI) to enhance their avidity towards Rapa. The fusion of FKBP to these nanoparticles slowed the terminal half-life of drug release to 57.8h. To determine if this class of drug carriers has potential applications in vivo, FSI/Rapa was administered to mice carrying a human breast cancer model (MDA-MB-468). Compared to free drug, FSI encapsulation significantly decreased gross toxicity and enhanced the anti-cancer activity. In conclusion, protein polymer nanoparticles decorated with the cognate receptor of a high potency, low solubility drug (Rapa) efficiently improved drug loading capacity and its release. This approach has applications to the delivery of Rapa and its analogs; furthermore, this strategy has broader applications in the encapsulation, targeting, and release of other potent small molecules.

Predicting transition temperatures of elastin-like polypeptide fusion proteins

Elastin-like polypeptides (ELPs) are thermally sensitive peptide polymers that undergo thermally triggered phase separation and this behavior is imparted to soluble proteins when they are fused to an ELP. The transition temperature of the ELP fusion protein is observed to be different than that of a free ELP, indicating that the surface properties of the fused protein modulate the thermal behavior of ELPs. Understanding this effect is important for the rational design of applications that exploit the phase transition behavior of ELP fusion proteins. We had previously developed a biophysical model that explained the effect of hydrophobic proteins on depressing the transition temperature of ELP fusion proteins relative to free ELP. Here, we extend the model to elucidate the effect of hydrophilic proteins on the thermal behavior of ELP fusion proteins. A linear correlation was found between overall residue composition of accessible protein surface weighted by a characteristic transition temperature for each residue and the difference in transition temperatures between the ELP protein fusion and the corresponding free ELP. In breaking down the contribution of residues to polar, nonpolar, and charged, the model revealed that charged residues are the most important parameter in altering the transition temperature of an ELP fusion relative to the free ELP.

Injectable protease-operated depots of glucagon-like peptide-1 provide extended and tunable glucose control

Peptide drugs are an exciting class of pharmaceuticals increasingly used for the treatment of a variety of diseases; however, their main drawback is a short half-life, which dictates multiple and frequent injections and an undesirable "peak-and-valley" pharmacokinetic profile, which can cause undesirable side-effects. Synthetic prolonged release formulations can provide extended release of biologically active native peptide, but their synthetic nature can be an obstacle to production and utilization. Motivated by these limitations, we have developed a new and entirely genetically encoded peptide delivery system--Protease Operated Depots (PODs)--to provide sustained and tunable release of a peptide drug from an injectable s.c. depot. We demonstrate proof-of-concept of PODs, by fusion of protease cleavable oligomers of glucagon-like peptide-1, a type-2 diabetes drug, and a thermally responsive, depot-forming elastin-like-polypeptide that undergoes a thermally triggered inverse phase transition below body temperature, thereby forming an injectable depot. We constructed synthetic genes for glucagon-like peptide-1 PODs and demonstrated their high-yield expression in Escherichia coli and facile purification by a nonchromatographic scheme we had previously developed. Remarkably, a single injection of glucagon-like peptide-1 PODs was able to reduce blood glucose levels in mice for up to 5 d, 120 times longer than an injection of the native peptide drug. These findings demonstrate that PODs provide the first genetically encoded alternative to synthetic peptide encapsulation schemes for sustained delivery of peptide therapeutics.

Expression and purification of the antimicrobial peptide cecropin AD by fusion with cationic elastin-like polypeptides

Cationic elastin-like polypeptides (CELP) are thermally responsive polypeptides that undergo an inverse temperature phase transition, and the recombinant CELP fusion proteins may be purified by inverse transition cycling (ITC). To obtain high-purity antimicrobial peptide cecropin AD (CAD), CELP was placed at the N-terminus of CAD and the expression vector pET28a-CELP-CAD was constructed. The expression vector was then transformed into Escherichia coli BL21 (DE3) to express the recombinant protein. After three rounds of ITC, enterokinase digestion and another hot spin, 1.2mg recombinant CAD was purified from 100ml culture medium. The antimicrobial test indicated that the high-purity CAD had strong antimicrobial activity against E. coli and Staphylococcus aureus.

Interleukin-1 receptor antagonist: a new therapy for type 2 diabetes mellitus

Various complex mechanisms and their multifactorial pathways decisively provoke low-grade local and systemic inflammation in β-cells of pancreatic islets and peripheral tissues to induce β-cells' dysfunction and apoptosis, insulin resistance, and ultimately, overt type 2 diabetes mellitus (T2DM). Conventional antidiabetic agents are being less popular, as they have some potential adverse effects. Currently, many anti-inflammatory therapeutic modalities are being investigated to abate the infuriating effects of inducers of T2DM and among them, interleukin-1 receptor antagonist (IL-1Ra) is the only one that has been approved by US Food and Drug Administration. We have compared IL-1Ra with other anti-inflammatory agents and conventional antidiabetic agents. Although, IL-1Ra has broad-spectrum anti-inflammatory activities, it also has some limitations due to its short half-life. To overcome the problem of short half-life of IL-1Ra, recently, we fused IL-1Ra in recombinant human serum albumin and expressed it in Pichia pastoris. Its bioactivity was also checked by IL-1-induced A375.S2 apoptotic cells. Furthermore, we have also formulated IL-1Ra with Pluronic F-127-based thermosensitive gel and investigated its in vitro characteristics to prolong its therapeutic effects. Further studies are required to investigate its therapeutic effects against diabetes and diabetes-associated complications.

Fusions of elastin-like polypeptides to pharmaceutical proteins

Elastin-like polypeptides (ELPs) are a class of stimulus-responsive biopolymers whose physicochemical properties and biocompatibility are particularly suitable for in vivo applications, such as drug delivery and tissue engineering. The lower critical solution temperature (LCST) behavior of ELPs allows them to be utilized as soluble macromolecules below their LCST, or as self-assembled nanoscale particles such as micelles, micron-scale coacervates, or viscous gels above their LCST, depending on the ELP architecture. As each ELP sequence is specified at its genetic level, functionalization of an ELP with peptides and proteins is simple to accomplish by the fusion of a gene encoding an ELP with that of the peptide or protein of interest. Protein ELP fusions, where the appended protein serves a therapeutic or targeting function, are suitable for applications in which the ELP can improve the systemic pharmacokinetics and biodistribution of the protein, or can be used as an injectable depot for sustained, local protein delivery. Here we describe considerations in the design of therapeutic protein ELP fusions and provide details of their gene design, expression, and purification.

Elastomeric polypeptides

Elastomeric polypeptides are very interesting biopolymers and are characterized by rubber-like elasticity, large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Their useful properties have motivated their use in a wide variety of materials and biological applications. This chapter focuses on elastin and resilin - two elastomeric biopolymers - and the recombinant polypeptides derived from them (elastin-like polypeptides and resilin-like polypeptides). This chapter also discusses the applications of these recombinant polypeptides in the fields of purification, drug delivery, and tissue engineering.

Thermo-targeted drug delivery of geldanamycin to hyperthermic tumor margins with diblock elastin-based biopolymers

The tumor margins are the barrier to hepatocellular carcinoma (HCC) eradication for tumors>3 cm. Indeed, inadequately treated tumor margins commonly result in local and regional HCC recurrence with increased size and mass. Tumor recurrence is a common problem with chemotherapy, radiotherapy, thermal ablation, and/or surgical resection, by the inability to properly treat the tumor core and the tumor margins. Here we present novel thermosensitive biopolymer-drug conjugates for thermo-targeted chemotherapy at hyperthermic isotherms produced by focal, locoregional thermal ablation. The chemotherapeutic target is heat shock protein 90 (HSP90), a key molecular chaperone of several, and potent pro-oncogenic pathways including Akt, Raf-1, and mutated p53 that is upregulated in HCC. To inhibit HSP90, we have chosen geldanamycin (GA), a potent HSP90 inhibitor. GA has gained significant attention for its low IC50 ~ 1 nM and inhibition of Akt and Raf-1, amongst other critical pro-oncogenic pathways. Despite such evidence, clinical trials of GA have not shown promise due to off-target toxicity and poor formulation design. Here, we propose using diblock elastin-based biopolymers as a Ringsdorf macromolecular GA solubilizer--a new generation containing functional poly(Asp)/(Glu) blocks for facile drug conjugation and an ELP block for thermo-targeting of hyperthermic ablative margins. GA release is controlled by pH-sensitive, covalent hydrazone bonds with the biopolymer backbone to avoid systemic toxicity and off-target effects. The resultant biopolymer-conjugates form stable nanoconstructs and display tunable, acute phase transitions at high temperatures. Drug release kinetics are favorable with or without the presence of serum. Thermo-targeted chemotherapy and synchronous thermal ablation provide a unique opportunity for simultaneous destruction of the HCC ablative margins and tumor core for focal, locoregional control of HCC.