Quantitation of secreted proteins using mCherry fusion constructs and a fluorescent microplate reader

Characterising the structural and cellular role of immunoglobulin C-terminal lysine in secretory pathways

Improved understanding of expression of recombinant immunoglobulin (IgG)-based therapies can decrease manufacturing process costs and bring down costs to patients. Deletion of C-terminal Lysine (C-Lys) from IgG molecules has been shown to greatly impact yield. This study set out to characterise structural components of IgG C-terminal variants which modulate protein expression by examination of the consequences of mutations at the C-terminal of IgG on expression and by the use of fluorescent C-terminal fragment fusion proteins. Cell-based and cell-free experiments were also implemented to characterise how the C-terminal differentially engages with cellular pathways to modulate expression. IgG variants engineered by removal of the C-terminal Lys were expressed at significantly lower rates than control variants by CHO (and HEK) cells. Engineered constructs of mCherry fused with short regions of the C-terminal regions of IgG mimicked the ordering of expressability observed for IgG variants. These fluorescent C-terminal fragment fusions offered the potential to profile how sequences (and point mutations) modified expression. Via combinations of cell and cell-free systems, screening across a range of variants of IgG and mCherry reporter constructs has shown that interactions between specific C-terminal amino acid sequences and the ribosome can regulate the rate and extent of expression. This study highlights the importance of amino acid sequence regulatory events determining the efficiency of production of desirable recombinant proteins, showing that wildtype C-terminal lysine is a necessary capping molecule for IgG1 expression. From a wider perspective, these data are especially significant towards the design of novel entities. The approach has also provided information about novel short C-terminal tags which may be used to provide selective synthesis of specific subunits in the production of multisubunit products. Alternative strategies for removing C-terminal amino acid heterogeneity whilst maintaining efficient rates of expression have been provided.

Oriented Insertion of ESR-Containing Hybrid Proteins in Proteoliposomes

Microbial rhodopsins comprise a diverse family of retinal-containing membrane proteins that convert absorbed light energy to transmembrane ion transport or sensory signals. Incorporation of these proteins in proteoliposomes allows their properties to be studied in a native-like environment; however, unidirectional protein orientation in the artificial membranes is rarely observed. We aimed to obtain proteoliposomes with unidirectional orientation using a proton-pumping retinal protein from Exiguobacterium sibiricum, ESR, as a model. Three ESR hybrids with soluble protein domains (mCherry or thioredoxin at the C-terminus and Caf1M chaperone at the N-terminus) were obtained and characterized. The photocycle of the hybrid proteins incorporated in proteoliposomes demonstrated a higher pK_a of the M state accumulation compared to that of the wild-type ESR. Large negative electrogenic phases and an increase in the relative amplitude of kinetic components in the microsecond time range in the kinetics of membrane potential generation of ESR-Cherry and ESR-Trx indicate a decrease in the efficiency of transmembrane proton transport. On the contrary, Caf-ESR demonstrates a native-like kinetics of membrane potential generation and the corresponding electrogenic stages. Our experiments show that the hybrid with Caf1M promotes the unidirectional orientation of ESR in proteoliposomes.

Site-Specific and Tunable Co-immobilization of Proteins onto Magnetic Nanoparticles via Spy Chemistry

Co-immobilization of multiple proteins onto one nanosupport has large potential in mimicking natural multiprotein complexes and constructing efficient cascade biocatalytic systems. However, control of different proteins regarding their spatial arrangement and loading ratio remains a big challenge, and protein co-immobilization often requires the use of purified proteins. Herein, built upon our recently designed SpyTag-functionalized magnetic nanoparticles (MNPs), we established a modular MNP platform for site-specific, tunable, and cost-effective protein co-immobilization. SpyCatcher-fused enhanced green fluorescent protein (i.e., EGFP-SpyCatcher) and mCherry red fluorescent protein (i.e., RFP-SpyCatcher) were designed and conjugated on MNPs, and the immobilized proteins showed 3-7-fold enhancement in storage stability and greatly improved stability against the freeze-thaw process compared to free proteins. The protein-conjugated MNPs also retained desirable colloidal stability and magnetic responsiveness, enabling facile proteins' recovery. Also, one-pot co-immobilization of the two proteins could be fine-tuned with their feed ratios. In addition, MNPs could selectively and efficiently co-immobilize both SpyCatcher-fused proteins from combined cell lysates without purification, offering a convenient and cost-effective approach for multiprotein immobilization. This MNP platform provides a facile and efficient tool to construct bionano hybrid materials (i.e., protein-based MNPs) and multiprotein systems for a variety of industrial and green chemistry applications.

mCherry fusions enable the subcellular localization of periplasmic and cytoplasmic proteins in Xanthomonas sp

Fluorescent markers are a powerful tool and have been widely applied in biology for different purposes. The genome sequence of Xanthomonas citri subsp. citri (X. citri) revealed that approximately 30% of the genes encoded hypothetical proteins, some of which could play an important role in the success of plant-pathogen interaction and disease triggering. Therefore, revealing their functions is an important strategy to understand the bacterium pathways and mechanisms involved in plant-host interaction. The elucidation of protein function is not a trivial task, but the identification of the subcellular localization of a protein is key to understanding its function. We have constructed an integrative vector, pMAJIIc, under the control of the arabinose promoter, which allows the inducible expression of red fluorescent protein (mCherry) fusions in X. citri, suitable for subcellular localization of target proteins. Fluorescence microscopy was used to track the localization of VrpA protein, which was visualized surrounding the bacterial outer membrane, and the GyrB protein, which showed a diffused cytoplasmic localization, sometimes with dots accumulated near the cellular poles. The integration of the vector into the amy locus of X. citri did not affect bacterial virulence. The vector could be stably maintained in X. citri, and the disruption of the α-amylase gene provided an ease screening method for the selection of the transformant colonies. The results demonstrate that the mCherry-containing vector here described is a powerful tool for bacterial protein localization in cytoplasmic and periplasmic environments.

A novel system to map protein interactions reveals evolutionarily conserved immune evasion pathways on transmissible cancers

Around 40% of humans and Tasmanian devils (Sarcophilus harrisii) develop cancer in their lifetime, compared to less than 10% for most species. In addition, devils are affected by two of the three known transmissible cancers in mammals. Immune checkpoint immunotherapy has transformed human medicine, but a lack of species-specific reagents has limited checkpoint immunology in most species. We developed a cut-and-paste reagent development system and used the fluorescent fusion protein system to show that immune checkpoint interactions are conserved across 160,000,000 years of evolution, CD200 is highly expressed on transmissible tumor cells, and coexpression of CD200R1 can block CD200 surface expression. The system's versatility across species was demonstrated by fusing a fluorescent reporter to a camelid-derived nanobody that binds human programmed death ligand 1. The evolutionarily conserved pathways suggest that naturally occurring cancers in devils and other species can be used to advance our understanding of cancer and immunological tolerance.

Peroxisome proliferator-activated receptor gamma-ligand-binding domain mutations associated with familial partial lipodystrophy type 3 disrupt human trophoblast fusion and fibroblast migration

The transcription factor peroxisome proliferator‐activated receptor gamma (PPARG) is essential for placental development, and alterations in its expression and/or activity are associated with human placental pathologies such as pre‐eclampsia or IUGR. However, the molecular regulation of PPARG in cytotrophoblast differentiation and in the underlying mesenchyme remains poorly understood. Our main goal was to study the impact of mutations in the ligand‐binding domain (LBD) of the PPARG gene on cytotrophoblast fusion (PPARG^E352Q) and on fibroblast cell migration (PPARG^R262G/PPARG^L319X). Our results showed that, compared to cells with reconstituted PPARG^WT, transfection with PPARG^E352Q led to significantly lower PPARG activity and lower restoration of trophoblast fusion. Likewise, compared to PPARG^WT fibroblasts, PPARG^R262G/PPARG^L319X fibroblasts demonstrated significantly inhibited cell migration. In conclusion, we report that single missense or nonsense mutations in the LBD of PPARG significantly inhibit cell fusion and migration processes.

Simultaneous in situ visualization and quantitation of dual antigens adsorbed on adjuvants using high content analysis

Aim: Traditional antigenicity assay requires antigen recovery from the particulate adjuvants prior to analysis. An in situ method was developed for interrogating vaccine antigens with monoclonal antibodies while being adsorbed on adjuvants. Materials & methods: The fluorescence imaging-based high content analysis was used to visualize the antigen distribution on adjuvant agglomerates and to analyze the antigenicity for adsorbed antigens. Results: Simultaneous visualization and quantitation were achieved for dual antigens in a bivalent human papillomavirus vaccine with uniquely labeled antibodies. Good agreement was observed between the in situ multiplexed assays with well-established sandwich enzyme-linked immunosorbent assays. Conclusion: The streamlined procedures and the amenability for multiplexing make the in situ antigenicity analysis a favorable choice for in vitro functional assessment of bionanoparticles as vaccine antigens.

A Large Stokes Shift Fluorescent Protein Constructed from the Fusion of Red Fluorescent mCherry and Far-Red Fluorescent BDFP1.6

Phycobiliproteins are constituents of phycobilisomes that can harvest orange, red, and far-red light for photosynthesis in cyanobacteria and red algae. Phycobiliproteins in the phycobilisome cores, such as allophycocyanins, absorb far-red light to funnel energy to the reaction centers. Therefore, allophycocyanin subunits have been engineered as far-red fluorescent proteins, such as BDFP1.6. However, most current fluorescent probes have small Stokes shifts, which limit their applications in multicolor bioimaging. mCherry is an excellent fluorescent protein that has maximal emittance in the red spectral range and a high fluorescence quantum yield, and thus, can be used as a donor for energy transfer to a far-red acceptor, such as BDFP1.6, by FRET. In this study, mCherry was fused with BDFP1.6, which resulted in a highly bright far-red fluorescent protein, BDFP2.0, with a large Stokes shift (≈79 nm). The excitation energy was absorbed maximally at 587 nm by mCherry and transferred to BDFP1.6 efficiently; thus emitting strong far-red fluorescence maximally at 666 nm. The effective brightness of BDFP2.0 in mammalian cells was 4.2-fold higher than that of iRFP670, which has been reported as the brightest far-red fluorescent protein. The large Stokes shift of BDFP2.0 facilitates multicolor bioimaging. Therefore, BDFP2.0 not only biolabels mammalian cells, including human cells, but also biolabels various intracellular components in dual-color imaging.

Nucleic acid-induced potentiation of matrix metalloproteinase-9 enzymatic activity

Matrix metalloproteinases (MMPs) play varied roles in normal biology and diseases where, depending on the context, both inhibition and enhancement of the enzymatic activity may be beneficial. However, there are very few reports of positive modulators of MMP activity. We report that polynucleotides, including single-stranded DNA, RNA, and even double-stranded DNA, bind to and enhance the enzymatic activity of MMP9. This enhancement of MMP9 catalytic activity is not shared by biologically active polycationic molecules suggesting nonspecific charge screening as an unlikely mechanism. Deletion construct and MMP1, 2, and 3 studies suggest that the type-II fibronectin repeat domains of the enzyme appear to play a role in mediating the nucleotide potentiation of MMP9 activity. Single-stranded DNA enhances nerve growth factor-induced MMP9-dependent neurite extension in pheochromocytoma 12 cells providing evidence for potential biological significance of the nucleotide-mediated allosteric enhancement of the catalytic activity.

Secreted dual reporter assay with Gaussia luciferase and the red fluorescent protein mCherry

The availability of a wide range of reporter proteins, which can easily be quantitated, has had a major impact on many fields of biomedical research. In some experiments with tissue culture cells, it is necessary to control for differences in transfection efficiency and in other expression parameters. This requirement has been very conveniently met with the popular dual luciferase assay. Its disadvantages are the requirement for cell lysis, the inability to analyze the same cells repeatedly, and the cost, at least in its most commonly used commercial format. Here we describe a novel dual reporter assay with the naturally secreted luciferase from Gaussia princeps as the main reporter protein and a secreted version of the red fluorescent protein mCherry as internal standard. After first measuring mCherry fluorescence in the medium, an enzyme buffer with coelenterazine as substrate is added to the same sample to trigger a glow-type luminescence of the luciferase. The simple and cheap assay can easily be adapted to a variety of experimental situations. As a case in point, we have developed a panel of Gaussia luciferase reporter genes for transcriptional activation assays with estrogen and glucocorticoid response elements, and with response elements for fusion proteins with the Gal4 DNA binding domain for use in mammalian cells. Our secreted dual reporter assay should be an attractive alternative to the currently available commercial kits.

Neonicotinoid-induced pathogen susceptibility is mitigated by Lactobacillus plantarum immune stimulation in a Drosophila melanogaster model

Pesticides are used extensively in food production to maximize crop yields. However, neonicotinoid insecticides exert unintentional toxicity to honey bees (Apis mellifera) that may partially be associated with massive population declines referred to as colony collapse disorder. We hypothesized that imidacloprid (common neonicotinoid; IMI) exposure would make Drosophila melanogaster (an insect model for the honey bee) more susceptible to bacterial pathogens, heat stress, and intestinal dysbiosis. Our results suggested that the immune deficiency (Imd) pathway is necessary for D. melanogaster survival in response to IMI toxicity. IMI exposure induced alterations in the host-microbiota as noted by increased indigenous Acetobacter and Lactobacillus spp. Furthermore, sub-lethal exposure to IMI resulted in decreased D. melanogaster survival when simultaneously exposed to bacterial infection and heat stress (37 °C). This coincided with exacerbated increases in TotA and Dpt (Imd downstream pro-survival and antimicrobial genes, respectively) expression compared to controls. Supplementation of IMI-exposed D. melanogaster with Lactobacillus plantarum ATCC 14917 mitigated survival deficits following Serratia marcescens (bacterial pathogen) septic infection. These findings support the insidious toxicity of neonicotinoid pesticides and potential for probiotic lactobacilli to reduce IMI-induced susceptibility to infection.

Nanoparticle-Based and Bioengineered Probes and Sensors to Detect Physiological and Pathological Biomarkers in Neural Cells

Nanotechnology, a rapidly evolving field, provides simple and practical tools to investigate the nervous system in health and disease. Among these tools are nanoparticle-based probes and sensors that detect biochemical and physiological properties of neurons and glia, and generate signals proportionate to physical, chemical, and/or electrical changes in these cells. In this context, quantum dots (QDs), carbon-based structures (C-dots, grapheme, and nanodiamonds) and gold nanoparticles are the most commonly used nanostructures. They can detect and measure enzymatic activities of proteases (metalloproteinases, caspases), ions, metabolites, and other biomolecules under physiological or pathological conditions in neural cells. Here, we provide some examples of nanoparticle-based and genetically engineered probes and sensors that are used to reveal changes in protease activities and calcium ion concentrations. Although significant progress in developing these tools has been made for probing neural cells, several challenges remain. We review many common hurdles in sensor development, while highlighting certain advances. In the end, we propose some future directions and ideas for developing practical tools for neural cell investigations, based on the maxim "Measure what is measurable, and make measurable what is not so" (Galileo Galilei).

Functional Roles of N-Linked Glycosylation of Human Matrix Metalloproteinase 9

Matrix metalloproteinase-9 (MMP-9) is a secreted endoproteinase with a critical role in the regulation of the extracellular matrix and proteolytic activation of signaling molecules. Human (h)MMP-9 has two well-defined N-glycosylation sites at residues N38 and N120; however, their role has remained mostly unexplored partly because expression of the N-glycosylation-deficient N38S has been difficult due to a recently discovered single nucleotide polymorphism-dependent miRNA-mediated inhibitory mechanism. hMMP-9 cDNA encoding amino acid substitutions at residues 38 (modified-S38, mS38) or 120 (N120S) were created in the background of a miRNA-binding site disrupted template and expressed by transient transfection. hMMP-9 harboring a single mS38 replacement secreted well, whereas N120S, or a double mS38/N120S hMMP-9 demonstrated much reduced secretion. Imaging indicated endoplasmic reticulum (ER) retention of the non-secreted variants and co-immunoprecipitation confirmed an enhanced strong interaction between the non-secreted hMMP-9 and the ER-resident protein calreticulin (CALR). Removal of N-glycosylation at residue 38 revealed an amino acid-dependent strong interaction with CALR likely preventing unloading of the misfolded protein from the ER chaperone down the normal secretory pathway. As with other glycoproteins, N-glycosylation strongly regulates hMMP-9 secretion. This is mediated, however, through a novel mechanism of cloaking an N-glycosylation-independent strong interaction with the ER-resident CALR.

LMAN1 (ERGIC-53) is a potential carrier protein for matrix metalloproteinase-9 glycoprotein secretion

Matrix metalloproteinase-9 (MMP-9) is a secreted glycoprotein with a major role in shaping the extracellular matrix and a detailed understanding of the secretory mechanism could help identify methods to correct diseases resulting from dysregulation of secretion. MMP-9 appears to follow a canonical secretory pathway through a quality control cycle in the endoplasmic reticulum (ER) before transport of the properly folded protein to the Golgi apparatus and beyond for secretion. Through a complementation assay, we determined that LMAN1, a well-studied lectin-carrier protein, interacts with a secretion-competent N-glycosylated MMP-9 in the ER while N-glycosylation-deficient secretion-compromised MMP-9 does not. In contrast, co-immunoprecipitation demonstrated protein interaction between LMAN1 and secretion-compromised N-glycosylation-deficient MMP-9. MMP-9 secretion was reduced in the LMAN1 knockout cell line compared to control cells confirming the functional role of LMAN1. These observations support the role of LMAN1 as a lectin-carrier protein mediating efficient MMP-9 secretion.