Green Fluorescent Protein Chimeras Research Articles

Increased ionic strength triggers multiple conformations in both apo and holo forms of bacterial ferric binding protein.

This study combines molecular dynamics (MD) simulations with solution X-ray scattering measurements to investigate the range of conformations that can be achieved by a pH/ionic strength (IS) sensitive protein and to quantify its distinct populations. To explore how the conformational multiplicity of proteins might be modified in the environmental niches of biological media, we focus on the periplasmic protein FbpA from H. influenzae which is a part of the mechanism developed by bacteria to capture iron from higher organisms. We examine iron-binding/release mechanisms of FbpA in varying conditions simulating its unique biological environment. The collected SAXS data complemented by SEC analyses and binding assays point to multiple conformations at physiological IS while they are well-explained by single x-ray structures in a 15 mM buffer. Moreover, by fitting the SAXS data with unique conformations sampled by a series of MD simulations carried out under conditions mimicking the buffers, we quantify with high accuracy the populations of the occupied substates. Furthermore, we find the D52A mutant that we predicted by coarse-grained computational approaches to allosterically control the iron binding site in FbpA responds to the environmental changes in our experiments with varied conformational selection scenarios. We show an application of the environment dependence of the conformers by designing a genetically encoded iron biosensor as a chimera of FbpA and green fluorescent protein using the D52 region as the insertion point. This work exemplifies how unifying a range of experimental and computational techniques provides platforms for achieving the next generation of applications that put protein dynamics rather than the static structure at the centerstage. Support by Turkish Atomic Energy Authority, TUBITAK grant no 121Z329 and a scholarship to GL through 2214-A program. Measurements conducted at EMBL-Hamburg.

PolyQ-Expanded Mutant Huntingtin Forms Inclusion Body Following Transient Cold Shock in a Two-Step Aggregation Mechanism.

Age-dependent formation of insoluble protein aggregates is a hallmark of many neurodegenerative diseases. We are interested in the cell chemistry that drives the aggregation of polyQ-expanded mutant Huntingtin (mHtt) protein into insoluble inclusion bodies (IBs). Using an inducible cell model of Huntington's disease, we show that a transient cold shock (CS) at 4 °C followed by recovery incubation at temperatures of 25-37 °C strongly and rapidly induces the compaction of diffuse polyQ-expanded HuntingtinExon1-enhanced green fluorescent protein chimera protein (mHtt) into round, micron size, cytosolic IBs. This transient CS-induced mHtt IB formation is independent of microtubule integrity or de novo protein synthesis. The addition of millimolar concentrations of sodium chloride accelerates, whereas urea suppresses this transient CS-induced mHtt IB formation. These results suggest that the low temperature of CS constrains the conformation dynamics of the intrinsically disordered mHtt into labile intermediate structures to facilitate de-solvation and hydrophobic interaction for IB formation at the higher recovery temperature. This work, along with our previous observation of the effects of heat shock protein chaperones and osmolytes in driving mHtt IB formation, underscores the primacy of mHtt structuring and rigidification for H-bond-mediated cross-linking in a two-step mechanism of mHtt IB formation in living cells.

An in vitro and in vivo study of the brain-targeting effects of an epidermal growth factor-functionalized cholera toxin-like chimeric protein

The development of neuroprotective drugs has proven to be extremely difficult because of the blood-brain barrier. Intranasal administration is thought to transport the drug from the nasal cavity along the olfactory and trigeminal nerves to the brain, thus bypassing the blood-brain barrier. However, macromolecular protein drugs have low delivery efficiency via this route in general. We hypothesized that an innocuous cholera toxin-like chimeric protein could better enhance the efficiency of protein delivery through the intranasal route. To test this hypothesis, we designed an enhanced green fluorescent protein (EGFP) chimera to evaluate the effect of the cholera toxin (CT) as a carrier for drug delivery into the brain. Then, the EGFP was replaced with epidermal growth factor (EGF) in the chimeric protein, and the therapeutic effect of the new chimeric protein was studied in an LPS-induced neuritis mouse model. The results suggest that the CT-like chimeric protein can bypass the blood-brain barrier and enter the brain in approximately 30 min. This EGF chimeric protein can effectively protect the spatial cognitive ability of and confer anti-anxiety protection to mice. The results indicate that cholera toxin-like chimeric proteins are potential tools for effectively delivering macromodecular drugs into the brain through intranasal administration.

Identification of nuclear localization signals in the human homeoprotein MSX1.

MSX1 is one of the homeoproteins with the homeodomain (HD) sequence, which regulates proliferation and differentiation of mesenchymal cells. In this study, we investigated the nuclear localization signal (NLS) in the MSX1 HD by deletion and amino acid substitution analyses. The web-based tool NLStradamus predicted 2 putative basic motifs in the N- and C-termini of the MSX1 HD. Green fluorescent protein (GFP) chimera studies revealed that NLS1 (161RKHKTNRKPR170) and NLS2 (216NRRAKAKR223) were independently insufficient for robust nuclear localization. However, they can work cooperatively to promote nuclear localization of MSX1, as was shown by the 2 tandem NLS motifs partially restoring functional NLS, leading to a significant nuclear accumulation of the GFP chimera. These results demonstrate a unique NLS motif in MSX1, which consists of an essential single core motif in helix-I, with weak potency, and an auxiliary subdomain in helix-III, which alone does not have nuclear localization potency. Additionally, other peptide sequences, other than predicted 2 motifs in the spacer, may be necessary for complete nuclear localization in MSX1 HD.

Upregulation of Phosphatidylinositol 3-Kinase (PI3K) Enhances Ethylene Biosynthesis and Accelerates Flower Senescence in Transgenic Nicotiana tabacum L.

Phosphatidylinositol 3-kinase (PI3K) is a key enzyme that phosphorylates phosphatidylinositol at 3’-hydroxyl position of the inositol head group initiating the generation of several phosphorylated phosphatidylinositols, collectively referred to as phosphoinositides. The function of PI3K in plant senescence and ethylene signal transduction process was studied by expression of Solanum lycopersicum PI3K in transgenic Nicotiana tabacum, and delineating its effect on flower senescence. Detached flowers of transgenic tobacco plants with overexpressed Sl-PI3K (OX) displayed accelerated senescence and reduced longevity, when compared to the flowers of wild type plants. Flowers from PI3K-overexpressing plants showed enhanced ethylene production and upregulated expression of 1-aminocyclopropane-1-carboxylic acid oxidase 1 (ACO1). Real time polymerase chain reaction (PCR) analysis showed that PI3K was expressed at a higher level in OX flowers than in the control. Seedlings of OX-lines also demonstrated a triple response phenotype with characteristic exaggerated apical hook, shorter hypocotyls and increased sensitivity to 1-aminocyclopropane-1-carboxylate than the control wild type seedlings. In floral tissue from OX-lines, Solanum lycopersicum phosphatidylinositol 3-kinase green fluorescent protein (PI3K-GFP) chimera protein was localized primarily in stomata, potentially in cytoplasm and membrane adjacent to stomatal pores in the guard cells. Immunoblot analysis of PI3K expression in OX lines demonstrated increased protein level compared to the control. Results of the present study suggest that PI3K plays a crucial role in senescence by enhancing ethylene biosynthesis and signaling.

Construction of a plasmid coding for green fluorescent protein tagged cathepsin L and data on expression in colorectal carcinoma cells.

The endo-lysosomal cysteine cathepsin L has recently been shown to have moonlighting activities in that its unexpected nuclear localization in colorectal carcinoma cells is involved in cell cycle progression (Tamhane et al., 2015) [1]. Here, we show data on the construction and sequence of a plasmid coding for human cathepsin L tagged with an enhanced green fluorescent protein (phCL-EGFP) in which the fluorescent protein is covalently attached to the C-terminus of the protease. The plasmid was used for transfection of HCT116 colorectal carcinoma cells, while data from non-transfected and pEGFP-N1-transfected cells is also shown. Immunoblotting data of lysates from non-transfected controls and HCT116 cells transfected with pEGFP-N1 and phCL-EGFP, showed stable expression of cathepsin L-enhanced green fluorescent protein chimeras, while endogenous cathepsin L protein amounts exceed those of hCL-EGFP chimeras. An effect of phCL-EGFP expression on proliferation and metabolic states of HCT116 cells at 24 h post-transfection was observed.

Nuclear cathepsin L activity is required for cell cycle progression of colorectal carcinoma cells.

Prominent tasks of cysteine cathepsins involve endo-lysosomal proteolysis and turnover of extracellular matrix constituents or plasma membrane proteins for maintenance of intestinal homeostasis. Here we report on enhanced levels and altered subcellular localization of distinct cysteine cathepsins in adenocarcinoma tissue in comparison to adjacent normal colon. Immunofluorescence and immunoblotting investigations revealed the presence of cathepsin L in the nuclear compartment in addition to its expected endo-lysosomal localization in colorectal carcinoma cells. Cathepsin L was represented as the full-length protein in the nuclei of HCT116 cells from which stefin B, a potent cathepsin L inhibitor, was absent. Fluorescence activated cell sorting analyses with synchronized cell cultures revealed deceleration of cell cycle progression of HCT116 cells upon inhibition of cathepsin L activity, while expression of cathepsin L-enhanced green fluorescent protein chimeras accelerated S-phase entry. We conclude that the activity of cathepsin L is high in the nucleus of colorectal carcinoma cells because of lacking stefin B inhibitory activity. Furthermore, we hypothesize that nuclear cathepsin L accelerates cell cycle progression of HCT116 cells thereby supporting the notion that cysteine cathepsins may play significant roles in carcinogenesis due to deregulated trafficking.

Two amino acid sequences direct Aspergillus nidulans protein kinase C (PkcA) localization to hyphal apices and septation sites

The Aspergillus nidulans ortholog of protein kinase C (pkcA) is involved in the organism’s putative cell wall integrity (CWI) pathway, and PkcA also is highly localized at growing tips and forming septa. In the present work we identify the regions within PkcA that are responsible for its localization to hyphal tips and septation sites. To this end, we used serially truncated pkcA constructs and expressed them as green fluorescent protein (GFP) chimeras and identified two regions that direct PkcA localization. The first region is a 10 amino-acid sequence near the carboxyl end of the C2 domain that is required for localization to hyphal tips. Proteins containing this sequence also localize to septation sites. A second region between C2 and C1B (encompassing C1A) is sufficient for localization to septation sites but not to hyphal tips. We also report that localization to hyphal tips and septation sites alone is not sufficient for truncated constructs to complement hypersensitivity to the cell wall compromising agent calcofluor white in a strain bearing a mutation in the pkcA gene. Taken together, these results suggest that localization and stress response might be independent.

Regulation of microRNA to the expression of matrix metalloproteinases in bone marrow-derived cells in mice with choroidal neovascularization

Background Matrix metalloproteinases (MMPs) play important roles in the formation of choroidal neovascularization (CNV), but its mail origin is not ocular cells in situ.Bone marrow-derived cells (BMCs) participate in the formation of CNV and is probably a primary source of expressing MMPs in CNV.MMP-2/MMP-13 is speculated to be the regulating target genes of miR188-5p. Objective This study was to verify whether BMCs are the main source of MMPs, and whether the MMP-2/MMP-13 expression is potentially regulated by miR188-5p. Methods BMCs expressed green fluorescent protein (GFP) from transgenic female C57BL/6J mice were transplanted to female wild-type C57BL/6J mice to establish C57BL/6J. GFP chimeras models, and 42 mice with chimerisms more than 85% by flow cytometry were included as the experimental group.Other 42 wild-type C57BL/6J mice without the BMCs transplantation were enrolled as the control group.CNV was induced by laser coagulation of retinas on the mice of both groups.MMP-2/MMP-13 levels in the retinochoroid tissue were quantified by ELISA at day 1, 3, 5, 7, 10, 14, and 28 after photocoagulation.The expression of miR188-5p mRNA in the retinochoroid tissue was assayed by real-time quantitative PCR (RT-qPCR).Immunofluorescence stain and fluorescent in situ hybridization were used to identify the MMP-2/MMP-13 and miR188-5p expressed by GFP-positive BMCs in CNV, and the expression level was quantified by images analysis. Results The proportion of GFP+mouse mononuclear cells was (90.67±3.02)% in the C57BL/6J.GFP chimeras.The concentration changes of MMP-2/MMP-13 in retinochoroid homogenate showed a same tendency with the lapse of time between the experimental group and the control group (MMP-2:F=0.060, P=0.810;MMP-13:F=0.012, P=0.915).The expression level was zoomed in retinochoroid tissue after induce of CNV with the maximal value on the third day in both groups, and the proportion in the experimental group was 64.21%;while the expression level of MMP-13 was slowly raised after induce of CNV with the peak at the seventh day, and the proportion in the experimental group was 79.61%.A complementary association point of miR188-5p was exhibited in the 3'-untranslated regions of MMP-2 or MMP-13 by target gene prediction.The expression level of miR188-5p mRNA in the BMCs of CNV area was sharply declined after induce of CNV with the lowest value on the seventh day.A negative correlation was found between the expressing level of miR188-5p and MMP-13 protein (r=-0.868, P<0.05) as well as early stage of expression level of MMP-2 protein (r=-0.997, P<0.05). Conclusions The elevation of MMP-2/MMP-13 expression levels is associated with the formation of CNV, and the regulation of miR188-5p expression in the BMCs of CNV area is responsible for increase of MMP-2/MMP-13 expression. The tendency of miR188-5p expression is inversed with MMP-2/MMP-13. Key words: Choroidal neovascularization; Matrix metalloproteinase; Bone marrow cell; MicroRNA

Fluobodies against Bioactive Natural Products and their Application in Fluorescence-Linked Immunosorbent Assay

An enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody (MAb), Fab antibody, and single-chain variable fragment (scFv) antibody has become one of the most promising analytical methods owing to its rapidity, sensitivity, and reliability. Recently, a chimera of green fluorescent protein (GFP) with a scFv antibody, named fluobody, was proposed as a probe for an alternative immunosorbent assay; i.e., fluorescence-linked immunosorbent assay (FLISA). In this FLISA, an even more sensitive, simple, and rapid immunoassay can be performed by detecting the highly sensitive fluorophore of GFP that is genetically and directly fused to the scFv antibody. In addition, the time- and cost-consuming secondary antibody reaction and the following enzyme-substrate reaction, necessary for conventional ELISA, can be avoided, making it possible to complete the assay more rapidly. Focusing on naturally occurring bioactive products, fluobody recognizing 1,4-naphthoquinone, plumbagin and triterpenoid saponin, ginsenosides were successfully expressed in Escherichia coli (E. coli) and applied to FLISA. The construction, the expression, and the potential use of fluobody in quantitative/qualitative analysis of bioactive natural products are reviewed in this article.

Ectopic bone formation cannot occur by hydroxyapatite/β-tricalcium phosphate bioceramics in green fluorescent protein chimeric mice

Many studies have shown that calcium phosphate ceramics (CP) have osteoconductive and osteoinductive properties; however, the exact mechanism of bone induction has not yet been reported. This study was performed to investigate if destroying immunological function will influence osteogenesis, to explain the mechanism which is unclear. In this study, twenty C57BL/6 mice were divided into two groups (n=10), in group 1, a hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) ceramic was implanted into both the left and right leg muscles of each mouse; in group 2, ten mice experienced lethal irradiation, then were injected bone marrow (BM) cells from green fluorescent protein (GFP) transgenic mice by tail veil, after bone marrow transplantation (BMT), heart, liver, spleen, lung, kidney, and muscle were harvested for biological analysis, after the GFP chimera model was established successfully, the same HA/β-TCP ceramic was implanted into both leg muscles of each mouse immediately after irradiation. 45 and 90 days after implantation, the ceramics of the two groups were harvested to perform with hematoxylin and eosin (HE) and immunohistochemistry (IHC) staining; the results showed that there was no bone formation in group 2, while new bone tissues were detected in group 1. Our findings suggest that the BM cell from GFP transgenic mice is a good biomarker and it could set a good platform for chimera model; it also shows that BM cell is one of cell resources of bone induction, and destruction of immune function will impede osteoinduction by CP. Overall, our results may shed light on clear mechanism study of bone induction in the future.

Establishment of Sf9 Transformants Constitutively Expressing PBAN Receptor Variants: Application to Functional Evaluation

To facilitate further evaluation of pheromone biosynthesis activating neuropeptide receptor (PBANR) functionality and regulation, we generated cultured insect cell lines constitutively expressing green fluorescent protein chimeras of the recently identified Bombyx mori PBANR (BommoPBANR) and Pseudaletia separata PBANR (PsesePBANR) variants. Fluorescent chimeras included the BommoPBANR-A, -B, and -C variants and the PsesePBANR-B and -C variants. Cell lines expressing non-chimeric BommoPBANR-B and -C variants were also generated. Functional evaluation of these transformed cell lines using confocal laser microscopy revealed that a Rhodamine Red-labeled PBAN derivative (RR-C10PBANR2K) specifically co-localized with all of the respective PBANR variants at the plasma membrane. Near complete internalization of the fluorescent RR-C10PBANR2K ligand 30 min after binding was observed in all cell lines except those expressing the BommoPBANR-A variant, in which the ligand/receptor complex remained at the plasma membrane. Fluorescent Ca2+ imaging further showed that the BommoPBANR-A cell line exhibited drastically different Ca2+ mobilization kinetics at a number of RR-C10PBANR2K concentrations including 10 μM. These observations demonstrate a clear functional difference between the BommoPBANR-A variant and the BommoPBANR-B and -C variants in terms of receptor regulation and activation of downstream effector molecules. We also found that, contrary to previous reports, ligand-induced internalization of BommoPBANR-B and BommoPBANR-C in cell lines stably expressing these variants occurred in the absence of extracellular Ca2+.

Monitoring Viral‐Mediated Membrane Fusion Using Fluorescent Reporter Methods

A simple and real-time cell-based assay of membrane fusion employing a pair of engineered novel reporter proteins is described. The reporter proteins are chimeras of split Renilla luciferase (RL) and split green fluorescent protein (GFP). This reporter allows us to perform both quantitative (RL mode) and visible (GFP mode) membrane fusion assays in live cells. The kinetic assay enabled by this method helps understand the mechanism of membrane fusion mediated by a viral envelope protein. This assay system is also suitable for the screening of potential inhibitors. The timing of inhibition by a particular inhibitor can be analyzed by time-dependent addition of the inhibitor. Although this unit demonstrates the application of the method for the analysis of HIV-1 envelope protein, the reporter can be applied to analyses of various other viral envelope proteins.

A chimera of green fluorescent protein with single chain variable fragment antibody against ginsenosides for fluorescence-linked immunosorbent assay

A chimera of green fluorescent protein extracted from Aequorea coerulescens (AcGFP), a mutant that has been codon optimized for mammalian expression, with single-chain variable fragment (scFv) antibody against ginsenoside Re (GRe-scFv), named fluobody, has been successfully expressed in Escherichia coli ( E. coli) to develop simple, speedy, and sensitive fluorescence-linked immunosorbent assay (FLISA). Two chimera proteins were constructed to contain GRe-scFv at the C-terminus of AcGFP (C-fluobody) and at the N-terminus of AcGFP (N-fluobody). These fluobodies were then purified by ion metal affinity chromatography and refolded by stepwise dialysis. The characterization of both fluobodies revealed that C-fluobody was found to be appropriate probe for FLISA as compare with N-fluobody. Furthermore, improvement of limit of detection (LOD) was observed in FLISA using C-fluobody (10 ng/mL) due to its strong fluorescence intensity of AcGFP compared with conventional enzyme-linked immunosorbent assay (ELISA) using parental monoclonal antibody against ginsenoside Re (G-Re), MAb-4G10 (100 ng/mL). Since some steps required in ELISA can be avoided in this present FLISA, speedy and sensitive immunoassay also could be performed using fluobody instead of monoclonal antibody and scFv.

Tracking Glideosome-Associated Protein 50 Reveals the Development and Organization of the Inner Membrane Complex of Plasmodium falciparum

The most deadly of the human malaria parasites, Plasmodium falciparum, has different stages specialized for invasion of hepatocytes, erythrocytes, and the mosquito gut wall. In each case, host cell invasion is powered by an actin-myosin motor complex that is linked to an inner membrane complex (IMC) via a membrane anchor called the glideosome-associated protein 50 (PfGAP50). We generated P. falciparum transfectants expressing green fluorescent protein (GFP) chimeras of PfGAP50 (PfGAP50-GFP). Using immunoprecipitation and fluorescence photobleaching, we show that C-terminally tagged PfGAP50-GFP can form a complex with endogenous copies of the linker protein PfGAP45 and the myosin A tail domain-interacting protein (MTIP). Full-length PfGAP50-GFP is located in the endoplasmic reticulum in early-stage parasites and then redistributes to apical caps during the formation of daughter merozoites. In the final stage of schizogony, the PfGAP50-GFP profile extends further around the merozoite surface. Three-dimensional (3D) structured illumination microscopy reveals the early-stage IMC as a doubly punctured flat ellipsoid that separates to form claw-shaped apposed structures. A GFP fusion of PfGAP50 lacking the C-terminal membrane anchor is misdirected to the parasitophorous vacuole. Replacement of the acid phosphatase homology domain of PfGAP50 with GFP appears to allow correct trafficking of the chimera but confers a growth disadvantage.

The SR-BI partner PDZK1 facilitates hepatitis C virus entry.

Entry of hepatitis C virus (HCV) into hepatocytes is a multi-step process that involves a number of different host cell factors. Following initial engagement with glycosaminoglycans and the low-density lipoprotein receptor, it is thought that HCV entry proceeds via interactions with the tetraspanin CD81, scavenger receptor class B type I (SR-BI), and the tight-junction proteins claudin-1 (CLDN1) and occludin (OCLN), culminating in clathrin-dependent endocytosis of HCV particles and their pH-dependent fusion with endosomal membranes. Physiologically, SR-BI is the major receptor for high-density lipoproteins (HDL) in the liver, where its expression is primarily controlled at the post-transcriptional level by its interaction with the scaffold protein PDZK1. However, the importance of interaction with PDZK1 to the involvement of SR-BI in HCV entry is unclear. Here we demonstrate that stable shRNA-knockdown of PDZK1 expression in human hepatoma cells significantly reduces their susceptibility to HCV infection, and that this effect can be reversed by overexpression of full length PDZK1 but not the first PDZ domain of PDZK1 alone. Furthermore, we found that overexpression of a green fluorescent protein chimera of the cytoplasmic carboxy-terminus of SR-BI (amino acids 479–509) in Huh-7 cells resulted in its interaction with PDZK1 and a reduced susceptibility to HCV infection. In contrast a similar chimera lacking the final amino acid of SR-BI (amino acids 479–508) failed to interact with PDZK1 and did not inhibit HCV infection. Taken together these results indicate an indirect involvement of PDZK1 in HCV entry via its ability to interact with SR-BI and enhance its activity as an HCV entry factor.

The cytosolic tail dipeptide Ile-Met of the pea receptor BP80 is required for recycling from the prevacuole and for endocytosis.

Pea (Pisum sativum) BP80 is a vacuolar sorting receptor for soluble proteins and has a cytosolic domain essential for its intracellular trafficking between the trans-Golgi network and the prevacuole. Based on mammalian knowledge, we introduced point mutations in the cytosolic region of the receptor and produced chimeras of green fluorescent protein fused to the transmembrane domain of pea BP80 along with the modified cytosolic tails. By analyzing the subcellular location of these chimera, we found that mutating Glu-604, Asp-616, or Glu-620 had mild effects, whereas mutating the Tyr motif partially redistributed the chimera to the plasma membrane. Replacing both Ile-608 and Met-609 by Ala (IMAA) led to a massive redistribution of fluorescence to the vacuole, indicating that recycling is impaired. When the chimera uses the alternative route, the IMAA mutation led to a massive accumulation at the plasma membrane. Using Arabidopsis thaliana plants expressing a fluorescent reporter with the full-length sequence of At VSR4, we demonstrated that the receptor undergoes brefeldin A-sensitive endocytosis. We conclude that the receptors use two pathways, one leading directly to the lytic vacuole and the other going via the plasma membrane, and that the Ileu-608 Met-609 motif has a role in the retrieval step in both pathways.

A chimera of green fluorescent protein with gelatinase binding and tumor targeting peptide

Matrix metalloproteinases (MMPs) are enzymes that can hydrolyze almost all constituents of extracellular matrix. An MMP subgroup, the gelatinases, has been focused during last years, since over-expression of gelatinase A (MMP-2) and gelatinase B (MMP-9) has been linked with severe homeostasis disorders such as tumor growth, metastasis formation, and chronic inflammation. In this study, a phage display library-derived novel antigelatinolytic decapeptide, the CTT-peptide, was expressed as a carboxyl terminal, histidine-tagged fusion with the green fluorescent protein (CTT–GFP) in Escherichia coli. In addition, a biologically intact chimera, in which residues in the CTT-peptide critical for gelatinase binding were replaced with alanine (Ala–CTT–GFP), was constructed. The GFP-fusion proteins were purified to homogeneity with a simple one-step procedure utilizing nickel affinity chromatography. The purified chimeras were tested for their binding properties to 4β-phorbol-12,13-butyrate (PdBu) activated, MMP-9 expressing THP-1 cells, and it was demonstrated that the CTT–GFP strongly bound to the cells, whereas Ala–CTT–GFP lacked the binding ability. Furthermore, the adherence of the CTT–GFP to MMP-9 expressing cells was demonstrated to be mediated by the CTT-moiety, since the binding could be dose-relatedly inhibited with increasing concentrations of synthetic soluble CTT-peptide. In conclusion, this novel tool, combining the gelatinase binding ability of the CTT-peptide with the fluorescing property of the GFP, should clearly improve both experimental and clinical studies of the role and function of gelatinases.

Aquaporin-4 (AQP4) Associations and Array Dynamics Probed by Photobleaching and Single-molecule Analysis of Green Fluorescent Protein-AQP4 Chimeras

The plasma membrane assembly of aquaporin-4 (AQP4) water channels into orthogonal arrays of particles (OAPs) involves interactions of AQP4 N-terminal domains. To study in live cells the site of OAP assembly, the size and dynamics of plasma membrane OAPs, and the heterotetrameric associations of AQP4, we constructed green fluorescent protein (GFP)-labeled AQP4 "long" (M1) and "short" (M23) isoforms in which GFP was inserted at the cytoplasm-facing N or C terminus or between Val-141 and Val-142 in the second extracellular loop of AQP4. The C-terminal and extracellular loop GFP insertions did not interfere with the rapid unrestricted membrane diffusion of GFP-labeled M1 or the restricted diffusion and OAP assembly of GFP-labeled M23. Photobleaching of brefeldin A-treated cells showed comparable and minimally restricted diffusion of M1 and M23, indicating that OAP assembly occurs post-endoplasmic reticulum. Single-molecule step photobleaching and intensity analysis of GFP-labeled M1 in the absence versus presence of excess unlabeled M1 or M23 with an OAP-disrupting mutation indicated heterotetrameric AQP4 association. Time-lapse total internal reflection fluorescence imaging of M23 in live cells at 37 degrees C indicated that OAPs diffuse slowly (D approximately 10(-12) cm(2)/s) and rearrange over tens of minutes. Our biophysical measurements in live cells thus reveal extensive AQP4 monomer-monomer and tetramer-tetramer interactions.

Live Imaging of Dense-core Vesicles in Primary Cultured Hippocampal Neurons

Observing and characterizing dynamic cellular processes can yield important information about cellular activity that cannot be gained from static images. Vital fluorescent probes, particularly green fluorescent protein (GFP) have revolutionized cell biology stemming from the ability to label specific intracellular compartments and cellular structures. For example, the live imaging of GFP (and its spectral variants) chimeras have allowed for a dynamic analysis of the cytoskeleton, organelle transport, and membrane dynamics in a multitude of organisms and cell types [1-3]. Although live imaging has become prevalent, this approach still poses many technical challenges, particularly in primary cultured neurons. One challenge is the expression of GFP-tagged proteins in post-mitotic neurons; the other is the ability to capture fluorescent images while minimizing phototoxicity, photobleaching, and maintaining general cell health. Here we provide a protocol that describes a lipid-based transfection method that yields a relatively low transfection rate (~0.5%), however is ideal for the imaging of fully polarized neurons. A low transfection rate is essential so that single axons and dendrites can be characterized as to their orientation to the cell body to confirm directionality of transport, i.e., anterograde v. retrograde. Our approach to imaging GFP expressing neurons relies on a standard wide-field fluorescent microscope outfitted with a CCD camera, image capture software, and a heated imaging chamber. We have imaged a wide variety of organelles or structures, for example, dense-core vesicles, mitochondria, growth cones, and actin without any special optics or excitation requirements other than a fluorescent light source. Additionally, spectrally-distinct, fluorescently labeled proteins, e.g., GFP and dsRed-tagged proteins, can be visualized near simultaneously to characterize co-transport or other coordinated cellular events. The imaging approach described here is flexible for a variety of imaging applications and can be adopted by a laboratory for relatively little cost provided a microscope is available.