A TAT-streptavidin fusion protein directs uptake of biotinylated cargo into mammalian cells

Enzyme Hinders HIV-1 Tat Viral Transport and Real-Time Measured with Nanopores

HIV-1 Tat protein, an intercellular transporter with a determinant function of delivering "information-rich" molecules in viral multiplication, was tryptic-hydrolyzed and real-time single molecule-monitored in a transmembrane pore. The electrokinetic studies revealed the catalytic and inhibitory effects on enzymatic digestion associated with Ca²⁺ and Cu²⁺ ions, respectively, in response to binding interactions with trypsin. Our strategy permits accurate and distinguishable sensing of Ca²⁺ and Cu²⁺ via an enzyme assay. In addition, considering the closer mimic of the real situation of HIV spread, measurements in the serum and on cells were also investigated. Transmembrane current measurements together with fluorescence microscopy imaging indicated the potential to perturb the Tat transport in the serum environment and on cells. Because the involved Tat proteolysis should prevent the occurrence of viral delivery, the presented method probably enables efficient hindrance to HIV-1 infection, in complementary to current traditional treatments.

A suitable and effective stepwise oxidative refolding procedure for highly-cationic tetrameric avidin in nucleic acid free conditions

Optimized conditions are needed to refold recombinant proteins from bacterial inclusion bodies into their biologically active conformations. In this study, we found two crucial requirements for efficient refolding of cationic tetrameric chicken avidin. The first step is to eliminate nucleic acid contaminants from the bacterial inclusion body. The electrostatic interactions between the remaining nucleic acids and proteins strongly enhanced protein aggregation during the refolding process. The cysteine specific reversible S-cationization procedure was successfully employed for large-scale preparation of nucleic acid free denatured protein without purification tag system. The second step is the intramolecular disulfide formation prior to refolding in dialysis removing denaturant. Disulfide intact monomeric avidin showed efficient formation of biologically active tetrameric conformation during the refolding process. Using this optimized refolding procedure, highly cationic avidin derivative designed as an intracellular delivery carrier of biotinylated protein was successfully prepared.

Microwave Assisted Sol-Gel Synthesis of Silica-Spider Silk Composites

This study introduces a simple and environmentally friendly method to synthesize silica-protein nanocomposite materials using microwave energy to solubilize hydrophobic protein in an aqueous solution of pre-hydrolyzed organo- or fluoro-silane. Sol-gel functionality can be enhanced through biomacromolecule incorporation to tune mechanical properties, surface energy, and biocompatibility. Here, synthetic spider silk protein and organo- and fluoro-silane precursors were dissolved and mixed in weakly acidic aqueous solution using microwave technology. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) images revealed the formation of spherical nanoparticles with sizes ranging from 100 to 500 nm depending, in part, on silane fluoro- or organo-side chain chemistry. The silane-protein interaction in the nanocomposite was assessed through infrared spectroscopy. Deconvoluted ATR-FTIR (Attenuated total reflectance Fourier-transform infrared spectroscopy) spectra revealed silane chemistry-specific conformational changes in the protein-silane nanocomposites. Relative to microwave-solubilized spider silk protein, the β structure content increased by 14% in the spider silk-organo-silica nanocomposites, but decreased by a net 20% in the spider silk-fluoro-silica nanocomposites. Methods of tuning the secondary structures, and in particular β-sheets that are the cross-linking moieties in spider silks and other self-assembling fibrillar proteins, may provide a unique means to promote protein interactions, favor subsequent epitaxial growth process, and enhance the properties of the protein-silane nanocomposites.

A potential peptide vector that allows targeted delivery of a desired fusion protein into the human breast cancer cell line MDA-MB-231

Effective control of breast cancer has been primarily hampered by a lack of tumor specificity in treatments. One potential way to improve targeting specificity is to develop novel vectors that specifically bind to and are internalized by tumor cells. Through a phage display library, an 11-L-amino acid peptide, PI (sequence, CASPSGALRSC), was selected. PI was labeled with fluorescein isothiocyanate (FITC) and named PI-FITC. Subsequently, the specific affinity of PI-FITC to MDA-MB-231 human breast cancer cells and other cancer cell lines was observed by confocal microscopy. Our previous study established that PI-FITC also shows affinity to Calu-1 human lung carcinoma cells and major histocompatibility complex class I antigen molecules; therefore, the cytomembrane proteins of the cell lines were analyzed to determine those that were common to the two cell lines and may be associated with transmembrane transduction. To further test the delivery ability of PI to MDA-MB-231 cells, PI-glutathione-S-transferase (GST) was constructed and the internalization of this fusion protein was visualized by immunofluorescence microscopy. The results revealed that PI exhibited specific affinity to MDA-MB-231 cells. Use of membrane transport inhibitors indicated that macropinocytosis and caveolin-mediated endocytosis may be involved in the endocytosis of PI. In addition, 11 membrane proteins common to MDA-MB-231 and Calu-1 may be associated with transmembrane transduction. In summary, PI was able to deliver PI-GST into MDA-MB-231 cells. Thus, PI could be modified to be a potential vector, and may contribute to the development of targeted therapeutic strategies for breast cancer.

Protein–polymer therapeutics: a macromolecular perspective

The development of protein–polymer hybrids emerged several decades ago with the vision that their synergistic combination will offer macromolecular hybrids with manifold features to succeed as the next generation therapeutics.

Slit diaphragm protein Neph1 and its signaling: a novel therapeutic target for protection of podocytes against glomerular injury

Podocytes are specialized epithelial cells that are critical components of the glomerular filtration barrier, and their dysfunction leads to proteinuria and renal failure. Therefore, preserving podocyte function is therapeutically significant. In this study, we identified Neph1 signaling as a therapeutic target that upon inhibition prevented podocyte damage from a glomerular injury-inducing agent puromycin aminonucleoside (PAN). To specifically inhibit Neph1 signaling, we used a protein transduction approach, where the cytoplasmic domain of Neph1 (Neph1CD) tagged with a protein transduction domain trans-activator of transcription was transduced in cultured podocytes prior to treatment with PAN. The PAN-induced Neph1 phosphorylation was significantly reduced in Neph1CD-transduced cells; in addition, these cells were resistant to PAN-induced cytoskeletal damage. The biochemical analysis using subfractionation studies showed that unlike control cells Neph1 was retained in the lipid raft fractions in the transduced cells following treatment with PAN, indicating that transduction of Neph1CD in podocytes prevented PAN-induced mislocalization of Neph1. In accordance, the immunofluorescence analysis further suggested that Neph1CD-transduced cells had increased ability to retain endogenous Neph1 at the membrane in response to PAN-induced injury. Similar results were obtained when angiotensin was used as an injury-inducing agent. Consistent with these observations, maintaining high levels of Neph1 at the membrane using a podocyte cell line overexpressing chimeric Neph1 increased the ability of podocytes to resist PAN-induced injury and PAN-induced albumin leakage. Using a zebrafish in vivo PAN and adriamycin injury models, we further demonstrated the ability of transduced Neph1CD to preserve glomerular function. Collectively, these results support the conclusion that inhibiting Neph1 signaling is therapeutically significant in preventing podocyte damage from glomerular injury.

Non-covalent ligand conjugation to biotinylated DNA nanoparticles using TAT peptide genetically fused to monovalent streptavidin

DNA nanoparticles (DNA NPs), which self-assemble from DNA plasmids and poly-L-lysine (pLL)-polyethylene glycol (PEG) block copolymers, transfect several cell types in vitro and in vivo with minimal toxicity and immune response. To further enhance the gene transfer efficiency of DNA NP and control its tropism, we established a strategy to efficiently attach peptide ligands to DNA NPs. The non-covalent biotin-streptavidin (SA) interaction was used for ligand conjugation to overcome problems associated with covalent conjugation methods. A fusion protein of SA with the HIV-1 TAT peptide was cloned, expressed, purified and attached to biotinylated DNA NPs. A modified SA system with tetrameric structure but monovalent biotin binding capacity was adopted and shown to reduce the aggregation of biotinylated DNA NPs compared to neutravidin. Compared to unmodified DNA NPs, TAT modified DNA NPs significantly enhanced in vitro gene transfer, particularly at low DNA concentrations. Studies of cellular uptake and cellular distribution of the DNA NPs indicated that attaching TAT enhanced binding of DNA NPs to cell surface but not internalization at high DNA concentrations. In vivo studies showed that TAT modified DNA NPs mediated equal level of gene transfer to the mouse airways via the luminal route compared to unmodified DNA NPs.

Controlling mesenchymal stem cell gene expression using polymer-mediated delivery of siRNA

siRNA treatment has great promise to specifically control gene expression and select cell behaviors but has delivery challenges limiting its use. Particularly for applications in regenerative medicine, uniform and consistent delivery of siRNA to control gene expression and subsequent stem cell functions, such as differentiation, is paramount. Therefore, a diblock copolymer was examined for its ability to effectively deliver siRNA to mesenchymal stem cells (MSCs). The diblock copolymers, which are composed of cationic blocks for siRNA complexation, protection, and uptake and pH-responsive blocks for endosomal escape, were shown to facilitate nearly 100% MSC uptake of siRNA. This is vastly superior to a commercially available control, DharmaFECT, which resulted in only ~60% siRNA positive MSCs. Moreover, the diblock copolymer, at conditions that result in excellent knockdown (down to ~10% of control gene expression), was cytocompatible, causing no negative effects on MSC survivability. In contrast, DharmaFECT/siRNA treatment resulted in only ~60% survivability of MSCs. Longitudinal knockdown after siRNA treatment was examined and protein knockdown persists for ~6 days regardless of delivery system (diblock copolymer or DharmaFECT). Finally, MSC phenotype and differentiation capacity was examined after treatment with control siRNA. There was no statistically significant differences on cell surface markers of diblock copolymer/siRNA or DharmaFECT/siRNA-treated or cells measured 2 weeks after siRNA delivery compared to untreated cells. Upon differentiation with typical media/culture conditions to adipogenic, chondrogenic, and osteogenic lineages and examination of histological staining markers, there was no discernible differences between treated and untreated cells, regardless of delivery mechanism. Thus, diblock copolymers examined herein facilitated uniform siRNA treatment of MSCs, inducing siRNA-specific gene and protein knockdown without adversely affecting MSC survival or differentiation capacity and therefore show great promise for use within regenerative medicine applications.

Efficient Intracellular Delivery of a Pro-Apoptotic Peptide With A pH-Responsive Carrier

A key challenge in developing protein therapeutics or imaging agents that work against cytosolic targets is the intracellular delivery barrier. Here, we show that the pH-responsive, membrane-destabilizing polymer, poly (propylacrylic acid) (PPAA), can strongly enhance target cell killing through the intracellular delivery of a functional proapoptotic peptide. The Bak BH3 peptide induces apoptosis via antagonization of suppressor targets such as Bcl-2 and Bcl-x(L). A genetically-engineered streptavidin that contains an N-terminal TAT peptide sequence was used to optimize the pinocytotic cell uptake of biotinylated BH3 peptide and end-biotinylated PPAA. Fluorescence microscopic analysis of DAPI-stained HELA cells was used to quantitate apoptosis. Approximately 30% of cells treated with TAT-SA:BH3 complexes revealed morphologically distinct nuclear condensation, a hallmark of apoptosis. The incorporation of biotinylated PPAA had the effect of markedly enhancing the killing effect of BH3 peptides by an additional 55% (p<0.001) to a total cell killing efficiency of 85%. Caspase-3 activity was up-regulated in a TAT-SA:BH3:PPAA dose-dependent manner. The induction of apoptosis with the TAT-SA:BH3:PPAA complex was abrogated with the L78A BH3 peptide, that had been previously shown to knock-out antagonization activity. The caspase and L78A peptide results demonstrate that the delivered BH3 is indeed working through the biologically relevant apoptosis signaling pathway. These studies establish the ability of PPAA to strongly enhance the intracellular delivery of a functional pro-apoptotic peptide. Together with the PPAA, the TAT-SA adaptor complex could prove useful as a carrier of peptide/protein cargo to cultured cells.

Targeting antibodies to the cytoplasm

A growing number of research consortia are now focused on generating antibodies and recombinant antibody fragments that target the human proteome. A particularly valuable application for these binding molecules would be their use inside a living cell, e.g., for imaging or functional intervention. Animal-derived antibodies must be brought into the cell through the membrane, whereas the availability of the antibody genes from phage display systems allows intracellular expression. Here, the various technologies to target intracellular proteins with antibodies are reviewed.

Logic-embedded vectors for intracellular partitioning, endosomal escape, and exocytosis of nanoparticles

A new generation of nanocarriers, logic-embedded vectors (LEVs), is endowed with the ability to localize components at multiple intracellular sites, thus creating an opportunity for synergistic control of redundant or dual-hit pathways. LEV encoding elements include size, shape, charge, and surface chemistry. In this study, LEVs consist of porous silicon nanocarriers, programmed for cellular uptake and trafficking along the endosomal pathway, and surface-tailored iron oxide nanoparticles, programmed for endosomal sorting and partitioning of particles into unique cellular locations. In the presence of persistent endosomal localization of silicon nanocarriers, amine-functionalized nanoparticles are sorted into multiple vesicular bodies that form novel membrane-bound compartments compatible with cellular secretion, while chitosan-coated nanoparticles escape from endosomes and enter the cytosol. Encapsulation within the porous silicon matrix protects these nanoparticle surface-tailored properties, and enhances endosomal escape of chitosan-coated nanoparticles. Thus, LEVs provide a mechanism for shielded transport of nanoparticles to the lesion, cellular manipulation at multiple levels, and a means for targeting both within and between cells.

Intracellular delivery of a proapoptotic peptide via conjugation to a RAFT synthesized endosomolytic polymer

Peptides derived from the third B-cell lymphoma 2 (Bcl-2) homology domain (BH3) can heterodimerize with antiapoptotic Bcl-2 family members to block their activity and trigger apoptosis. Use of these peptides presents a viable anticancer approach, but delivery barriers limit the broad application of intracellular-acting peptides as clinical therapeutics. Here, a novel diblock copolymer carrier is described that confers desirable pharmaceutical properties to intracellular-acting therapeutic peptides through site-specific molecular conjugation. This polymer was prepared using reversible addition-fragmentation chain transfer (RAFT) to form a pyridyl disulfide end-functionalized, modular diblock copolymer with precisely controlled molecular weight (M(n)) and low polydispersity (PDI). The diblock polymer (M(n) 19,000 g/mol, PDI 1.27) was composed of an N-(2-hydroxypropyl) methacrylamide (HPMA) first block (M(n) 13,800 g/mol, PDI 1.13) intended to enhance water solubility and circulation time. The second polymer block was a pH-responsive composition designed to enhance endosomal escape and consisted of equimolar quantities of dimethylaminoethyl methacrylate (DMAEMA), propylacrylic acid (PAA), and butyl methacrylate (BMA). A hemolysis assay indicated that the diblock polymer undergoes a physiologically relevant pH-dependent switch from a membrane inert (1% hemolysis, pH 7.4) to a membrane disruptive (61% hemolysis, pH 5.8) conformation. Thiol-disulfide exchange reactions were found to efficiently produce reversible polymer conjugates (75 mol % peptide reactivity with polymer) with a cell-internalized proapoptotic peptide. Microscopy studies showed that peptide delivered via polymer conjugates effectively escaped endosomes and achieved diffusion into the cytosol. Peptide-polymer conjugates also produced significantly increased apoptotic activity over peptide alone in HeLa cervical carcinoma cells as found using flow cytometric measurements of mitochondrial membrane depolarization (2.5-fold increase) and cell viability tests that showed 50% cytotoxicity after 6 h of treatment with 10 muM peptide conjugate. These results indicate that this multifunctional carrier shows significant promise for proapoptotic peptide cancer therapeutics and also as a general platform for delivery of peptide drugs with intracellular targets.

Cellular siRNA delivery using cell-penetrating peptides modified for endosomal escape

RNAi-mediated silencing of specific genes is a promising strategy for gene therapy. To utilize RNAi for therapy, an efficient and safe method for delivery of RNA into the cell cytosol is necessary. The plasma membrane is the primary, and most difficult, barrier for RNA to cross, because negatively charged RNA is strongly repulsed by the negatively charged membrane. A variety of cationic polymers can be used as RNA carriers by interacting with RNA and covering its negative charges to form a cell-penetrating complex. Among the emerging candidates for RNA carriers are cationic cell-penetrating peptides (CPPs), which can cross the plasma membrane and internalize into cells together with RNA. This review focuses on CPP-based RNA delivery strategies. In using CPP-based RNA delivery, most of the RNA internalized by the cell is entrapped in endosomes. Strategies for endosomal escape of RNAs are also reviewed.

Transtactin: a universal transmembrane delivery system for Strep-tag II-fused cargos

The delivery of molecules into cells poses a critical problem that has to be solved for the development of diagnostic tools and therapeutic agents acting on intracellular targets. Cargos which by themselves cannot penetrate cellular membranes due to their biophysical properties can achieve cell membrane permeability by fusion to protein transduction domains (PTDs). Here, we engineered a universal delivery system based on PTD-fused Strep-Tactin, which we named Transtactin. Biochemical characterization of Transtactin variants bearing different PTDs indicated high thermal stabilities and robust secondary structures. Internalization studies demonstrated that Transtactins facilitated simple and safe transport of Strep-tag II-linked small molecules, peptides and multicomponent complexes, or biotinylated proteins into cultured human cells. Transtactin-introduced cargos were functionally active, as shown for horseradish peroxidase serving as a model protein. Our results demonstrate that Transtactin provides a universal and efficient delivery system for Strep-tag II-fused cargos.

Antigen delivery with poly(propylacrylic acid) conjugation enhances MHC-1 presentation and T-cell activation

While many infectious diseases are controlled by vaccine strategies, important limitations continue to motivate the development of better antigen delivery systems. This study focuses on the use of a pH-sensitive polymeric carrier based on poly(propylacrylic acid) (PPAA) to address the need for more potent CD8 cytotoxic T-cell (CTL) responses. An MHC-1/CD8 CTL cell model system with ovalbumin as the protein antigen was used to test whether PPAA could enhance the delivery of ovalbumin into the MHC-1 display pathway. Ovalbumin was conjugated to poly(propylacrylic acid-co-pyridyldisulfide acrylate) (PPAA-PDSA) by disulfide exchange to make reversible conjugates that could be reduced by the glutathione redox system in the cytosol of antigen presenting cells. The PPAA-PDSA ovalbumin conjugates displayed the pH-sensitive membrane disruptive properties of the parent polymer as determined by their hemolysis activities (sharply active at the endosomal pH values of 6-6.5). The polymer-ovalbumin conjugates exhibited strong 22-fold increases in the MHC-1 presentation and ovalbumin-specific CTL activation compared to free ovalbumin. No CTL activation was observed with control conjugates of ovalbumin and poly(methylacrylic acid) (PMAA) that do not display membrane disruptive activies, suggesting that it is the membrane destabilizing properties of the polymer that result in increased MHC-1 display and CTL activation. Further mechanistic studies quantitated the time course of stable intracellular localization of radiolabeled conjugates. 52% of initially internalized PPAA-conjugated ovalbumin remained in the cells after 4 h, compared to less than 10% of ovalbumin or PMAA-ovalbumin. These results showing enhanced cytosolic delivery and MHC-1 presentation for the PPAA-antigen conjugates suggest that they warrant future characterization as a CD8-enhancing vaccine delivery system.

Efficient cytosolic delivery of molecular beacon conjugates and flow cytometric analysis of target RNA

Fluorescent microscopy experiments show that when 2'-O-methyl-modified molecular beacons (MBs) are introduced into NIH/3T3 cells, they elicit a nonspecific signal in the nucleus. This false-positive signal can be avoided by conjugating MBs to macromolecules (e.g. NeutrAvidin) that prevent nuclear sequestration, but the presence of a macromolecule makes efficient cytosolic delivery of these probes challenging. In this study, we explored various methods including TAT peptide, Streptolysin O and microporation for delivering NeutrAvidin-conjugates into the cytosol of living cells. Surprisingly, all of these strategies led to entrapment of the conjugates within lysosomes within 24 h. When the conjugates were pegylated, to help prevent intracellular recognition, only microporation led to a uniform cytosolic distribution. Microporation also yielded a transfection efficiency of 93% and an average viability of 86%. When cells microporated with MB-NeutrAvidin conjugates were examined via flow cytometry, the signal-to-background was found to be more than 3 times higher and the sensitivity nearly five times higher than unconjugated MBs. Overall, the present study introduces an improved methodology for the high-throughput detection of RNA at the single cell level.

Syntheses of highly fluorescent GFP-chromophore analogues

Eight B-containing compounds, i.e., 1a-h, were prepared as mimics of the green fluorescent protein (GFP) fluorophore. The underlying concept was that synthetic GFP chromophore analogues are not fluorescent primarily because of free rotation about an aryl-alkene bond (Figure 1b). This rotation is not possible in the beta-barrel of GFP; hence, the molecule is strongly fluorescent. In compounds 1a-h, radiationless decay via this mechanism is prevented by complexation of the BF2 entity. The target materials were prepared via two methods; most were obtained according to the novel route shown in Scheme 1b, but compound 1f was made via the procedure described in Scheme 2. Both syntheses involved formation of undesired compounds E-4a-h that formed simultaneously with the desired isomeric intermediates Z-4a-h. Both compounds form BF2 adducts, i.e., 1a-h and 5a-h, respectively. Methods used for spectroscopic characterization and differentiation of compounds in the series 1 and 5 are discussed, and these are supported by single-crystal X-ray diffraction analyses for compounds 1c, 5c, 1f, and 5f. Electronic spectra of compounds 1a-h and 5a-h were studied in detail. Those in the 5 series were shown to be only weakly fluorescent, but the 1 series were strongly fluorescent compounds (comparable to the boraindacene, BODIPY, dyes). Compounds 1g and 1h are water soluble, and 1h has particularly significant potential as a probe, since it also has a carboxylic acid group for attachment to biomolecules.

Cell studies of a three-component antisense MORF/tat/Herceptin nanoparticle designed for improved tumor delivery

The three-component nanoparticle of this investigation consisted of an anti-type I regulatory subunit alpha of the cyclic AMP-dependent protein kinase A (RIalpha) antisense phosphorodiamidate morpholino (MORF) oligomer, a tat peptide and the anti-HER2 Herceptin antibody each biotinylated and each linked via streptavidin and tested in SUM190 (HER2+), SUM149 (HER2-) and SK-BR-3 (HER2+) cells in culture, using both radioactivity and fluorescent labels on the antisense and control sense MORF. Within the nanoparticle, the antibody provides specific binding to the target cells, the tat improves cellular delivery and the MORF provides the specific retention of the radioactivity in the target cell nucleus. The results show that within the nanoparticle, the Herceptin was still able to bind to its determinant; that the MORF escaped entrapment with its mRNA-binding ability preserved and that the tat maintained its carrier function. Fluorescence microscopy showed evidence of antisense MORF internalization, separation from Herceptin and migration to the nucleus. In conclusion, streptavidin appears to provide an easy means of mixing and matching components to improve the tumor-specific targeting, cell membrane transport, pharmacokinetics and other properties of antisense and other oligomers. Combining the three components of this investigation with streptavidin apparently did not interfere with the properties of each component in cell culture and significantly improved delivery.

Genetic incorporation of the protein transduction domain of Tat into Ad5 fiber enhances gene transfer efficacy

Background

Human adenovirus serotype 5 (Ad5) has been widely explored as a gene delivery vector for a variety of diseases. Many target cells, however, express low levels of Ad5 native receptor, the Coxsackie-Adenovirus Receptor (CAR), and thus are resistant to Ad5 infection. The Protein Transduction Domain of the HIV Tat protein, namely PTD_tat, has been shown to mediate protein transduction in a wide range of cells. We hypothesize that re-targeting Ad5 vector via the PTD_tat motif would improve the efficacy of Ad5-mediated gene delivery.

Results

In this study, we genetically incorporated the PTD_tat motif into the knob domain of Ad5 fiber, and rescued the resultant viral vector, Ad5.PTD_tat. Our data showed the modification did not interfere with Ad5 binding to its native receptor CAR, suggesting Ad5 infection via the CAR pathway is retained. In addition, we found that Ad5.PTD_tat exhibited enhanced gene transfer efficacy in all of the cell lines that we have tested, which included both low-CAR and high-CAR decorated cells. Competitive inhibition assays suggested the enhanced infectivity of Ad5.PTD_tat was mediated by binding of the positively charged PTD_tat peptide to the negatively charged epitopes on the cells' surface. Furthermore, we investigated in vivo gene delivery efficacy of Ad5.PTD_tat using subcutaneous tumor models established with U118MG glioma cells, and found that Ad5.PTD_tat exhibited enhanced gene transfer efficacy compared to unmodified Ad5 vector as analyzed by a non-invasive fluorescence imaging technique.

Conclusion

Genetic incorporation of the PTD_tat motif into Ad5 fiber allowed Ad5 vectors to infect cells via an alternative PTD_tat targeting motif while retaining the native CAR-mediated infection pathway. The enhanced infectivity was demonstrated in both cultured cells and in in vivo tumor models. Taken together, our study identifies a novel tropism expanded Ad5 vector that may be useful for clinical gene therapy applications.

Enhanced transfection of tumor cells in vivo using "Smart" pH-sensitive TAT-modified pegylated liposomes

Liposomes have been prepared loaded with DNA (plasmid encoding for the green fluorescent protein, GFP) and additionally modified with TATp and PEG, with PEG being attached to the liposome surface via both pH-sensitive hydrazone and non-pH-sensitive bonds. The pGFP-loaded liposomal preparations have been administered intratumorarly in tumor-bearing mice and the efficacy of tumor cell transfection was followed after 72 h. The administration of pGFP-TATp-liposomes with non-pH-sensitive PEG coating has resulted in only minimal transfection of tumor cells because of steric hindrances for the liposome-to-cell interaction created by the PEG coat, which shielded the surface-attached TATp. At the same time, the administration of pGFP-TATp-liposomes with the low pH-detachable PEG resulted in at least three times more efficient transfection since the removal of PEG under the action of the decreased intratumoral pH leads to the exposure of the liposome-attached TATp residues, enhanced penetration of the liposomes inside tumor cells and more effective intracellular delivery of the pGFP. This result can be considered as an important step in the development of tumor-specific stimuli-sensitive drug and gene delivery systems.

Internalization of novel non-viral vector TAT-streptavidin into human cells

Background

The cell-penetrating peptide derived from the Human immunodeficiency virus-1 transactivator protein Tat possesses the capacity to promote the effective uptake of various cargo molecules across the plasma membrane in vitro and in vivo. The objective of this study was to characterize the uptake and delivery mechanisms of a novel streptavidin fusion construct, TAT_47–57-streptavidin (TAT-SA, 60 kD). SA represents a potentially useful TAT-fusion partner due to its ability to perform as a versatile intracellular delivery vector for a wide array of biotinylated molecules or cargoes.

Results

By confocal and immunoelectron microscopy the majority of internalized TAT-SA was shown to accumulate in perinuclear vesicles in both cancer and non-cancer cell lines. The uptake studies in living cells with various fluorescent endocytic markers and inhibiting agents suggested that TAT-SA is internalized into cells efficiently, using both clathrin-mediated endocytosis and lipid-raft-mediated macropinocytosis. When endosomal release of TAT-SA was enhanced through the incorporation of a biotinylated, pH-responsive polymer poly(propylacrylic acid) (PPAA), nuclear localization of TAT-SA and TAT-SA bound to biotin was markedly improved. Additionally, no significant cytotoxicity was detected in the TAT-SA constructs.

Conclusion

This study demonstrates that TAT-SA-PPAA is a potential non-viral vector to be utilized in protein therapeutics to deliver biotinylated molecules both into cytoplasm and nucleus of human cells.

Designed evolution of artificial metalloenzymes: protein catalysts made to order

Artificial metalloenzymes based on biotin-streptavidin technology, a "fusion" of chemistry and biology, illustrate how asymmetric catalysts can be improved and evolved using chemogenetic approaches.

Translocation and nuclear accumulation of monomer and dimer of HIV-1 Tat basic domain in triticale mesophyll protoplasts

Cellular internalization of cell-penetrating peptide HIV-1 Tat basic domain (RKKRRQRRR) was studied in Triticale cv AC Alta mesophyll protoplasts. Fluorescently labeled monomer (Tat) and dimer (Tat(2)) of Tat basic domain efficiently translocated through the plasma membrane of mesophyll protoplast and showed distinct nuclear accumulation within 10 min of incubation. Substitution of first arginine residue with alanine in Tat basic domain (M-Tat) severely reduced cellular uptake of the peptide (3.8 times less than Tat). Tat(2) showed greater cellular internalization than Tat (1.6 times higher). However, characteristics of cellular uptake remained same for Tat and Tat(2). Cellular internalization of Tat and Tat(2) was concentration dependent and non-saturable whereas no significant change in cellular uptake was observed even at higher concentrations of M-Tat. Low temperature (4 degrees C) remarkably increased cellular internalization of Tat as well as Tat(2) but M-Tat showed no enhanced uptake. Viability test showed that peptide treatment had no cytotoxic effect on protoplasts further indicating involvement of a common mechanism of peptide uptake at all the temperatures. Endocytic inhibitors nocodazole (10 muM), chloroquine (100 muM) and sodium azide (5 mM) did not show any significant inhibitory effect on cellular internalization of either Tat or Tat(2). These results along with stimulated cellular uptake at low temperature indicate that Tat peptide is internalized in the plant protoplasts in a non-endocytic and energy-independent manner. Competition experiments showed that non-labeled peptide did not inhibit or alter nuclear accumulation of fluorescent Tat or Tat(2) suggesting active transport to the nucleus was not involved. Studies in mesophyll protoplasts show that internalization pattern of Tat peptide is apparently similar to that observed in mammalian cell lines.

The taming of the cell penetrating domain of the HIV Tat: myths and realities

Protein transduction with cell penetrating peptides over the past several years has been shown to be an effective way of delivering proteins in vitro and now several reports have also shown valuable in vivo applications in correcting disease states. An impressive bioinspired phenomenon of crossing biological barriers came from HIV transactivator Tat protein. Specifically, the protein transduction domain of HIV Tat has been shown to be a potent pleiotropic peptide in protein delivery. Various approaches such as molecular modeling, arginine guanidinium head group structural strategy, multimerization of PTD sequence and phage display system have been applied for taming of the PTD. This has resulted in identification of PTD variants which are efficient in cell membrane penetration and cytoplasmic delivery. In spite of these state of the art technologies, the dilemma of low protein transduction efficiency and target specific delivery of PTD fusion proteins remains unsolved. Moreover, some misconceptions about PTD of Tat in the literature require considerations. We have assembled critical information on secretory, plasma membrane penetration and transcellular properties of Tat and PTD using molecular analysis and available experimental evidences.

Delivery of antibody-captured proteins into living cells using PTD-fused protein A

Protein transduction domain (PTD)-mediated protein delivery into animal cells is a useful technique for regulating cellular functions. Proteins captured by antibodies were delivered into living cells using an antibody/PTD-fused protein A complex. As a model protein, fluorescent-modified antibodies, captured by their respective primary antibody, were analyzed by fluorescence-activated cell sorting (FACS) which showed that the fluorescent-modified antibodies were directly delivered into cells. Peroxidase, captured by its specific antibody, was also delivered into cells and retained its activity.

Novel nanocomposites from spider silk-silica fusion (chimeric) proteins

Silica skeletal architectures in diatoms are characterized by remarkable morphological and nanostructural details. Silk proteins from spiders and silkworms form strong and intricate self-assembling fibrous biomaterials in nature. We combined the features of silk with biosilica through the design, synthesis, and characterization of a novel family of chimeric proteins for subsequent use in model materials forming reactions. The domains from the major ampullate spidroin 1 (MaSp1) protein of Nephila clavipes spider dragline silk provide control over structural and morphological details because it can be self-assembled through diverse processing methods including film casting and fiber electrospinning. Biosilica nanostructures in diatoms are formed in aqueous ambient conditions at neutral pH and low temperatures. The R5 peptide derived from the silaffin protein of Cylindrotheca fusiformis induces and regulates silica precipitation in the chimeric protein designs under similar ambient conditions. Whereas mineralization reactions performed in the presence of R5 peptide alone form silica particles with a size distribution of 0.5-10 microm in diameter, reactions performed in the presence of the new fusion proteins generate nanocomposite materials containing silica particles with a narrower size distribution of 0.5-2 microm in diameter. Furthermore, we demonstrate that composite morphology and structure could be regulated by controlling processing conditions to produce films and fibers. These results suggest that the chimeric protein provides new options for processing and control over silica particle sizes, important benefits for biomedical and specialty materials, particularly in light of the all aqueous processing and the nanocomposite features of these new materials.

The importance of valency in enhancing the import and cell routing potential of protein transduction domain-containing molecules

Protein transduction domains (PTDs) are peptides that afford the internalization of cargo macromolecules (including plasmid DNA, proteins, liposomes, and nanoparticles). In the case of polycationic peptides, the efficiency of PTDs to promote cellular uptake is directly related to their molecular mass or their polyvalent presentation. Similarly, the efficiency of routing to the nucleus increases with the number of nuclear localization signals (NLS) associated with a cargo. The quantitative enhancement, however, depends on the identity of the PTD sequence as well as the targeted cell type. Thus the choice and multivalent presentation of PTD and NLS sequences are important criteria guiding the design of macromolecules intended for specific intracellular localization. This review outlines synthetic and recombinant strategies whereby PTDs and signal sequences can be assembled into multivalent peptide dendrimers and promote the uptake and routing of their cargoes. In particular, the tetramerization domain of the tumour suppressor p53 (p53tet) is emerging as a useful scaffold to present multiple routing and targeting moieties. Short cationic peptides fused to the 31-residue long p53tet sequence resulted in tetramers displaying a significant enhancement (up to 1000 fold) in terms of their ability to be imported into cells and delivered to the cell nucleus in relation to their monomeric analogues. The design of future polycationic peptide dendrimers as effective delivering vehicles will need to incorporate selective cell targeting functions and provide solutions to the issue of endosomal entrapment.