Application of elastin-based nanoparticles displaying antibody binding domains for a homogeneous immunoassay

Functional decoration of elastin-like polypeptides-based nanoparticles with a modular assembly via isopeptide bond formation

Temperature-responsive elastin-like polypeptides (ELPs) exhibit a low critical solution temperature-type phase transition and offer potential as useful materials for the construction of nanoparticles. Herein, we developed a novel decoration method for ELP-based nanoparticles via isopeptide bond formation with the SnoopTag/SnoopCatcher system that is not affected by the heating process required for particle formation. A mixture of a fusion protein of ELP and poly(aspartic acid) (poly(D)), known as ELP-poly(D), and ELP-poly(D) fused with SnoopCatcher (ELP-poly(D)-SnC) formed protein nanoparticles as a result of the temperature responsiveness of ELP, with the resultant nanoparticles displaying the SnoopCatcher binding domain on their surfaces. In the present study, two model proteins fused to SnoopTag were displayed on the surfaces of protein nanoparticles constructed from ELP-poly(D)-SnC and ELP-poly(D). The model proteins are enhanced green fluorescent protein (EGFP) and Renilla luciferace (Rluc), which exhibits luminescent capability and weak thermostability, respectively. EGFP on the particle surface was found to retain 48.7% activity, while Rluc exhibited almost full activity, as calculated from the binding efficiency and nanoparticle activities recovered after purification. ELP-based nanoparticles containing the SnoopTag/SnoopCatcher system offer the opportunity for particle decoration with a wide range of functional proteins via isopeptide bond formation.

Affibody-Functionalized Elastin-like Peptide-Drug Conjugate Nanomicelle for Targeted Ovarian Cancer Therapy

Recombinant elastin-like polypeptides (ELPs) have emerged as an attractive nanoplatform for drug delivery due to their tunable genetically encoded sequence, biocompatibility, and stimuli-responsive self-assembly behaviors. Here, we designed and biosynthesized an HER2 (human epidermal growth factor receptor 2)-targeted affibody-ELP fusion protein (Z-ELP), which was subsequently conjugated with monomethyl auristatin E (MMAE) to build a protein-drug conjugate (Z-ELP-M). Due to its thermal response, Z-ELP-M can immediately self-assemble into a nanomicelle at physiological temperature. Benefiting from its active targeting and nanomorphology, Z-ELP-M exhibits enhanced cellular internalization and deep tumor penetration in vitro. Moreover, Z-ELP-M shows excellent tumor targeting and superior antitumor efficacy in HER2-positive ovarian cancer, demonstrating a relative tumor growth inhibition of 104.6%. These findings suggest that an affibody-functionalized elastin-like peptide-drug conjugate nanomicelle is an efficient strategy to improve antitumor efficacy and biosafety in cancer therapy.

Sensitive Detection of Tumor Cells Using Protein Nanoparticles with Multiple Displays of DNA Aptamers and Bioluminescent Reporters

Simple and effective detection methods for circulating tumor cells are essential for early detection and progression monitoring of tumors. The use of DNA aptamer and bioluminescence is expected to be a key tool for the simple, effective, and sensitive detection of tumor cells. Herein, we designed multifunctional protein nanoparticles for the detection of tumor cells using DNA aptamer and bioluminescence. Fusion proteins (ELP-poly(d)-POIs), composed of elastin-like polypeptide (ELP) fused with protein of interests (POIs) via poly(aspartic acid) (poly(d)), formed the protein nanoparticles based on the temperature responsivity of ELP sequences, leading to multiply displayed POIs on the protein nanoparticles. In the present study, we focused on porcine circovirus type 2 replication initiation protein (Rep), which covalently conjugated with DNA aptamers, and NanoLuc luciferase (Nluc), which emitted a strong bioluminescence, as POIs. ELP-poly(d)-Rep and ELP-poly(d)-Nluc were constructed and formed the protein nanoparticles with multiply displayed Nluc and Rep (DNA aptamer) that amplified the bioluminescence signal and tumor recognition ability. Mucin-1 (MUC1)-overexpressing human breast tumor MCF7 cells and MUC1-recognizing aptamer (MUC1 aptamer) were selected as models. The MUC1 aptamer-conjugated protein nanoparticles exhibited a 13.7-fold higher bioluminescence signal to MCF-7 cells than to human embryonic kidney 293 (HEK293) cells, which express low levels of MUC1. Furthermore, the protein nanoparticles could detect up to 70.7 cells/mL of MCF-7 cells from a cell suspension containing HEK-293. The protein nanoparticles with multiple Rep and Nluc show a great potential as a material for detecting CTCs.

Development of an enhanced immunoassay based on protein nanoparticles displaying an IgG-binding domain and luciferase

Detection of small amounts of target molecules with high sensitivity is important for the diagnosis of many diseases, including cancers, and is particularly important to detect early stages of disease. Here, we report the development of a temperature-responsive fusion protein (ELP-DCN) comprised of an elastin-like polypeptide (ELP), poly-aspartic acid (D), antibody-binding domain C (C), and NanoLuc luciferase (N). ELP-DCN proteins form nanoparticles above a certain threshold temperature that display an antibody-binding domain and NanoLuc luciferase on their surface. ELP-DCN nanoparticles can be applied for enhancement of immunoassay systems because they provide more antibody-binding sites and an increased number of luciferase molecules, resulting in an increase in assay signal. Here, we report the detection of human serum albumin (HSA) as a model protein using anti-HSA and ELP-DCN proteins. Upon formation of ELP-DCN nanoparticles, the detection limit improved tenfold compared to the monomeric form of ELP-DCN.

Biofabricating a Silk Scaffold as a Functional Microbial Trap

Silk fibroin produced from silkworms has been intensively utilized as a scaffold material for a variety of biotechnological applications owing to its remarkable mechanical strength, extensibility, biocompatibility, and ease of biofunctionalization. In this research, we engineered silk as a novel trap platform capable of capturing microorganisms. Specifically, we first fabricated the silk material into a silk sponge by lyophilization, yielding a 3D scaffold with porous microstructures. The sponge stability in water was significantly improved by ethanol treatment with elevated β-sheet content and crystallinity of silk. Next, we biofunctionalized the silk sponge with a poly-specific microbial targeting molecule, ApoH (apolipoprotein H), to enable a novel silk-based microbial trap. The recombinant ApoH engineered with an additional penta-tyrosine was assembled onto the silk sponge through the horseradish peroxidase (HRP) mediated dityrosine cross-linking. Last, the ApoH-decorated silk sponge was demonstrated to be functional in capturing our model microorganism targets, E. coli and norovirus-like particles. We envision that this biofabricated silk platform, capable of trapping a variety of microbial entities, could serve as a versatile scaffold for rapid isolation and enrichment of microbial samples toward future diagnostics and therapeutics. This strategy, in turn, can expedite advancing future biodevices with functionality and sustainability.

Construction of DNA-displaying nanoparticles by enzymatic conjugation of DNA and elastin-like polypeptides using a replication initiation protein

DNA-displaying nanoparticles comprised of conjugates of single-stranded DNA (ssDNA) and elastin-like polypeptide (ELP) were developed. ssDNA was enzymatically conjugated to ELPs via a catalytic domain of Porcine Circovirus type 2 replication initiation protein (pRep) fused to ELPs. Nanoparticles were formed upon heating to temperatures above the phase transition temperature due to the hydrophobicity of ELPs and the hydrophilicity of conjugated ssDNA. We demonstrated the applicability of the resultant nanoparticles as drug carriers with tumor-targeting properties by conjugating a DNA aptamer, which is known to bind to Mucin 1 (MUC1), to ELPs. DNA aptamer-displaying nanoparticles encapsulating the anti-cancer drug paclitaxel were able to bind to cells overexpressing MUC1 and induce cell death.

Direct Labeling of Protein Nanoparticles with Fluorescent Compounds for Immunoassay Applications

A fusion protein, designated ELP-D-C, comprised of a hydrophobic elastin-like polypeptide unit, a hydrophilic aspartic acid-rich peptide unit, and an antibody-binding domain as a functional unit, was constructed. Upon heat induction, ELP-D-C forms micellar nanoparticles displaying antibody-binding domains on their surfaces. The protein nanoparticles were able to incorporate hydrophobic fluorescent compounds and subsequently detect target molecules via antibody binding by the resulting fluorescence intensity, which was proportional to the log of the concentration of the target molecule.

Polymer nanoparticle sizes from dynamic light scattering and size exclusion chromatography: the case study of polysilanes

Dynamic light scattering (DLS) and size exclusion chromatography (SEC) are among the most popular methods for determining polymer sizes in solution. Taking dendritic and network polysilanes as a group of least soluble polymer substances, we critically compare and discuss the difference between nanoparticle sizes, obtained by DLS and SEC. Polymer nanoparticles are typically in poor solution conditions below the theta point and are therefore in the globular conformation. The determination of particle sizes in the presence of attractive interactions is not a trivial task. The only possibility to measure, aggregation-free, the true molecular size of polymer nanoparticles in such a solution regime, is to perform the experiment with a dilute solution of globules (below the theta point and above the miscibility line). Based on the results of our polysilane measurements, we come to a conclusion that DLS provides more reliable results than SEC for dilute solutions of globules. General implications for the size measurements of polymer nanoparticles in solution are discussed.