Cleavable Fusion Protein Research Articles

Expression, purification, and evaluation of in vivo anti-fibrotic activity for soluble truncated TGF-β receptor II as a cleavable His-SUMO fusion protein.

Excessive production of transforming growth factor-β1 (TGF-β1) and its binding to transforming growth factor-β receptor type II (TGF-βRII) promotes fibrosis by activation of the TGF-β1-mediated signaling pathway. Thus, the truncated extracellular domain of TGF-βRII (tTβRII) is a promising anti-fibrotic candidate, as it lacks the signal transduction domain. In this work, the native N-terminal tTβRII was prepared as a His-SUMO fusion protein (termed His-SUMO-tTβRII) in Escherichia coli strain BL21 (DE3). His-SUMO-tTβRII was expressed as a soluble protein under optimal conditions (6h of induction with 0.5mM IPTG at 37°C). His-SUMO-tTβRII was purified by Ni-NTA resin chromatography, and then cleaved with SUMO protease to release native tTβRII, which was re-purified using a Ni-NTA column. Approximately 12mg of native tTβRII was obtained from a one liter fermentation culture with no less than 95% purity. In vivo studies demonstrated that tTβRII prevented CCl4-induced liver fibrosis, as evidenced by the inhibition of fibrosis-related Col I and α-SMA protein expression in C57BL/6 mice. In addition, tTβRII downregulated phosphorylation of SMAD2/3, which partly repressed TGF-β1-mediated signaling. These data indicate that the His-SUMO expression system is an efficient approach for preparing native tTβRII that possesses anti-liver fibrotic activity, allowing for the large-scale production of tTβRII, which potentially could serve as an anti-fibrotic candidate for treatment of TGF-β1-related diseases.

Mass spectrometric revival of an l-rhamnose– and d-galactose–specific lectin from a lost strain of Streptomyces

Blood type B-specific Streptomyces sp. 27S5 hemagglutinin (SHA) was discovered and characterized in the 1970s. Although strain 27S5 has been lost, the purified SHA protein survived intact under frozen conditions and retained its activity. Using modern techniques, here we further characterized SHA. Fourier-transform ion cyclotron resonance MS analysis determined the average molecular mass of SHA as 13,314.67 Da. MS of digested SHA peptides, Streptomyces genomic database matching, and N-terminal sequencing solved the 131-residue amino acid sequence of SHA. We found that SHA is homologous to N-terminally truncated hypothetical proteins encoded by the genomes of Streptomyces lavendulae, Streptomyces sp. Mg1, and others. The gene of the closest homologue in S. lavendulae, a putative polysaccharide deacetylase (PDSL), encodes 68 additional N-terminal amino acids, and its C terminus perfectly matched the SHA sequence, except for a single Ala-to-Glu amino acid difference. We expressed recombinant SHA(PDSL-A108E) (rSHA) as an enzymatically cleavable fusion protein in Escherichia coli, and glycan microarray analyses indicated that refolded rSHA exhibits the blood type B- and l-rhamnose-specific characteristics of authentic SHA, confirming that rSHA is essentially identical with SHA produced by Streptomyces sp. 27S5. We noted that SHA comprises three similar domains, representing 70% of the protein, and that these SHA domains partially overlap with annotated clostridial hydrophobic with conserved W domains. Furthermore, examination of GFP-tagged SHA revealed binding to microbial surfaces. rSHA may be useful both for studying the role of SHA/clostridial hydrophobic with conserved W domains in carbohydrate binding and for developing novel diagnostics and therapeutics for l-rhamnose-containing microorganisms.

Isolation and Purification of Actin Homolog MreB from Caulobacter crescentus

Caulobacter crescentus is an important model for studying cell cycle regulation, cellular differentiation, and cell polarity. The perceived absence of a cytoskeletal network in bacteria was once considered a defining distinction between prokaryotic and eukaryotic cells. However, orhtologues of all three major classes of eukaryotic cytoskeletal proteins have been identified: FtsZ, a tubulin homolog, MreB and ParM, actin homologs, and CreS (crescentin) which appears to be an intermediate filament protein. MreB is required for the maintenance of the rod cell shape. MreB is organized in an axial spiral that is dynamically rearranged during the cell cycle. Little is known about the mechanisms regulating MreB polymerization. To this end, we aimed to purify MreB for use in in vitro polymerization assays. We used two schemes to purify C. crescentus MreB. The first method employs a cleavable GST‐MreB fusion protein overexpressed in E. coli. The second method takes advantage of buffer conditions that support either polymerization or depolymerization of MreB: MreB transitions between soluble and insoluble states, with purification by ultracentrifugation. Elucidation of MreB polymerization and depolymerization mechanisms has the potential to impact the design of chemotherapeutics affecting cell cycle regulation, cellular differentiation, and cell polarity. Supported by NIH T34GM008411

Half-life extension through albumin fusion technologies

Haemophilia B is characterized by a deficiency of coagulation factor IX (FIX), a protein that is important in the process of haemostasis and normal blood clotting. Recurrent bleeding into joints and soft tissues is the hallmark of severe haemophilia B. The goal of treatment is to prevent and manage haemorrhage and thereby reduce disabling joint and tissue damage, improve quality of life, and extend life expectancy. Current treatment with FIX replacement concentrates often requires repeated, frequent infusions, owing to the relatively short terminal half-life of FIX in the circulation. We have developed a unique technology for improving the biological characteristics of FIX in vivo. For this approach, recombinant FIX (rFIX) was genetically fused to albumin via a cleavable peptide linker. Constructs of the fusion protein were expressed in mammalian cells and characterized following purification. In vitro activation studies demonstrated that cleavage of the linker occurred in parallel with FIX activation. The molar specific clotting activity of the cleavable fusion protein (rIX-FP) was 10- to 30-fold greater than that of the fusion protein with non-cleavable linkers. In rats, rabbits, and FIX-deficient mice, the pharmacokinetics of rIX-FP were significantly improved compared with rFIX. Using the tail-clip bleeding model in FIX-deficient mice, rIX-FP effectively corrected the bleeding time and blood loss. These findings suggest that rIX-FP may be a promising therapy for the treatment of patients with haemophilia B.

In vitro- and in vivo-targeted tumor lysis by an MMP2 cleavable melittin-LAP fusion protein

Chemotherapy is one of the main treatment options for cancer, but the effectiveness of chemotherapeutic drugs is severely limited due to their systemic toxicity. Therefore, the need for a more targeted approach in tumor treatment is obvious. A tumor-activated agent would decrease systemic toxicity as well as increase the efficacy of the treatment. It has previously been shown that the latency of pro-TGF-beta is conferred by dimerization of two latency-associated peptides (LAP) that form a protective shield, which is cleaved off upon activation by matrix metalloproteinases (MMPs). It has also been shown that the fusion of this LAP peptide with other cytokines can confer their latency. In the present study, a recombinant adenovirus with a fusion gene encoding a tumor-activated pro-cytolytic peptide was made in which the LAP domain of TGF-beta was fused with melittin, a potent cytolytic toxin, with an MMP2 cleavage site in between the two. In vitro studies show that the melittin-MMP2-LAP recombinant adenovirus can be activated by MMP2 which leads to the release of free melittin to lyse the target cells. In vivo studies show approximately a 70% decrease in B16 tumor volume in melittin-MMP2-LAP recombinant adenovirus-treated mice as compared to control mice. No significant systemic toxicity was observed in the treated mice.

Diversity in Tissue Expression, Substrate Binding, and SCF Complex Formation for a Lectin Family of Ubiquitin Ligases

Post-translational modification of proteins regulates many cellular processes. Some modifications, including N-linked glycosylation, serve multiple functions. For example, the attachment of N-linked glycans to nascent proteins in the endoplasmic reticulum facilitates proper folding, whereas retention of high mannose glycans on misfolded glycoproteins serves as a signal for retrotranslocation and ubiquitin-mediated proteasomal degradation. Here we examine the substrate specificity of the only family of ubiquitin ligase subunits thought to target glycoproteins through their attached glycans. The five proteins comprising this FBA family (FBXO2, FBXO6, FBXO17, FBXO27, and FBXO44) contain a conserved G domain that mediates substrate binding. Using a variety of complementary approaches, including glycan arrays, we show that each family member has differing specificity for glycosylated substrates. Collectively, the F-box proteins in the FBA family bind high mannose and sulfated glycoproteins, with one FBA protein, FBX044, failing to bind any glycans on the tested arrays. Site-directed mutagenesis of two aromatic amino acids in the G domain demonstrated that the hydrophobic pocket created by these amino acids is necessary for high affinity glycan binding. All FBA proteins co-precipitated components of the canonical SCF complex (Skp1, Cullin1, and Rbx1), yet FBXO2 bound very little Cullin1, suggesting that FBXO2 may exist primarily as a heterodimer with Skp1. Using subunit-specific antibodies, we further demonstrate marked divergence in tissue distribution and developmental expression. These differences in substrate recognition, SCF complex formation, and tissue distribution suggest that FBA proteins play diverse roles in glycoprotein quality control.

Requirement of N-glycosylation for the secretion of recombinant extracellular domain of human Fas in HeLa cells

Apoptosis has been shown to be associated with altered glycosylation patterns and biosynthesis of glycoproteins. A major cell surface receptor involved in the induction of apoptosis is Fas that is activated by binding Fas ligand but can also be activated by binding anti-Fas antibody. In order to determine whether the Fas receptor is glycosylated, the extracellular domain of human Fas (shFas) was expressed as a cleavable fusion protein (shFas-Fc) in HeLa cells. These cells were shown to express activities of glycosyltransferases involved in N- and O-glycan biosynthesis. The secreted shFas-Fc was shown to be a glycoprotein with heterogeneous glycan chains. MALDI mass spectrometry revealed a disperse molecular weight of shFas with an average of 23.4kDa. Western blots of shFas-Fc secreted from tunicamycin treated transfected HeLa cells showed that only N-glycosylated glycoforms were secreted, while the unglycosylated shFas-Fc remained intracellular. The results suggest that both N-glycosylation sites of the extracellular domain of Fas are occupied with large N-glycans that play a role in the expression of the glycoprotein.

Functional expression of bitistatin, a disintegrin with potential use in molecular imaging of thromboembolic disease

Bitistatin is a single-chain disintegrin which contains 83 amino acids and is internally crosslinked with seven disulfide bonds. This platelet aggregation inhibitor, which binds with high affinity to the αIIbβ3 integrin, has potential use as the basis for a radiotracer to locate thrombi and emboli by scintigraphic imaging. A method amenable to large-scale, consistent production of bitistatin was sought. A synthetic gene coding for bitistatin was inserted into two different Escherichia coli expression vectors. One vector expressed recombinant bitistatin (rBitistatin) as a cleavable fusion protein and the other expressed rBitistatin as an isolated protein. In both cases, rBitistatin contained an additional amino acid (Gly) at the N-terminus compared with the native protein. The fusion protein was purified by affinity chromatography, then cleaved enzymatically to release rBitistatin, which was purified by reversed-phase high performance liquid chromatography (HPLC) to a single active form. The rBitistatin produced as an isolated protein was purified from cell lysate by HPLC in a reduced form, then refolded, and purified again by HPLC. Yields of active rBitistatin averaged 12 mg/L for expression as an isolated protein, 10 times as high as when the fusion protein was employed. Structural assays confirmed the expected mass and sequence of the product. Functional assays (inhibition of platelet aggregation in vitro, equilibrium binding to platelets in vitro, and binding of labeled protein to experimental thrombi and emboli in vivo) confirmed that rBitistatin retained the functional characteristics of native bitistatin.

A new strategy for glycoprotein synthesis: ligation of synthetic glycopeptides with truncated proteins expressed in E. coli as TEV protease cleavable fusion protein

We report here the use of TEV protease cleavable fusion proteins to produce glycosylated bioactive peptides and proteins. Bacterial expression was utilized to produce two fusion proteins, GPRT-C37-H6 and His-tagged interleukin-2 (amino acids 6–133), which when cleaved by the tobacco etch virus NIa protease (TEV protease) to generate HIV entry inhibitor peptide C37-H6 and a truncated version of the cytokine interleukin-2, both containing N-terminal cysteines. The N-terminal cysteine containing C37-H6 and truncated interleukin-2 were then joined to a synthetic glycopeptide thioester utilizing native chemical ligation under nondenaturing and denaturing conditions, respectively. The ligations of the glycopeptide to the C37-H6 peptide and the truncated interleukin-2 protein both proceeded in high yield, though the size, and physical properties of the two polypeptides differ greatly.

Functional expression and characterization of an acidic actinoporin from sea anemone Sagartia rosea

Src I is the first reported acidic actinoporin from sea anemone Sagartia rosea with a p I value of 4.8 and comprises 13.9% α-helix, 65.1% β-sheet, and 18.2% random coil. For structure–function studies, Src I was expressed in Escherichia coli as a cleavable fusion protein. Recombinant Src I exhibited obviously hemolytic activity, but the fusion protein Trx-Src I almost lost its hemolytic activity, suggesting the importance of the N-terminal amphiphilic α-helix for its functional activity. The cytotoxic effects of Src I depending on the toxin concentration and incubation time were also observed on cultured cells. Among five cell lines: NIH/3T3, U251, NSCLC, BEL-7402, and BGC-823, NSCLC was the most sensitive cells with ID 50 2.8 μg/ml and BGC-823 was the least sensitive cells with ID 50 7.4 μg/ml. After incubated with lipid SUVs, such as SM-SUVs and SM/PC-SUVs, the hemolytic activity of Src I was inhibited to some extent. When incubated with calcein-entrapped lipid LUVs, such as SM-LUVs, SM/PC-LUVs, and SM/PG-LUVs, Src I induced release of entrapped calcein. According to the interaction with lipid vesicles, we proposed that it was the membrane matrix made up of phospholipids, not a particular phospholipid that facilitates Src I to react properly.

Mitochondrial coupling factor 6 as an endogenous inhibitor of prostacyclin synthesis and an endogenous vasoconstrictor

The possible presence of an unknown prostacyclin-synthesis inhibitory substance has been reported in some strains of rats. We purified the inhibitory substance from the heart of spontaneously hypertensive rats by collecting active fractions after gel-filtration column chromatography and reverse-phase high performance liquid chromatography. The automated gas-phase sequencing indicated that the prostacyclin-inhibitory peptide was identical to coupling factor 6. Recombinant rat coupling factor 6, which was synthesized using a cleavable fusion protein strategy, attenuated baseline and bradykinin (10 −6 M)-induced prostacyclin synthesis and [ 3H] arachidonic acid (AA) release in human umbilical vein endothelial cells (HUVEC) in a dose-dependent manner. Exogenous AA- and prostaglandin H2-induced prostacyclin synthesis were unchanged even after treatment with 10 −7 M recombinant coupling factor 6. Baseline and bradykinin-induced [ 3H] AA release were suppressed by arachidonyl trifluoromethyl ketone, a relatively specific inhibitor of cytosolic phospholipase A 2 (PLA 2), and simultaneous administration of coupling factor 6 showed no further effect. Neither oleyloxyethyl phosphorylcholine nor bromoenol lactone affected AA release. Intravenous injection of recombinant coupling factor 6 increased arterial blood pressure in rats, whereas a specific antibody to coupling factor 6 decreased systemic blood pressure. We conclude that coupling factor 6 possesses a novel function of prostacyclin synthesis inhibition in endothelial cells via suppression of Ca 2+-dependent cytosolic PLA 2 and functions as an endogenous vasoconstrictor.

Purification and molecular characterization of recombinant rat betacellulin.

A method for the large scale expression and purification of rat betacellulin (BTC) from Escherichia coli has been developed using a cleavable fusion protein strategy. Insoluble fusion protein collected as inclusion bodies was dissolved in urea under reducing conditions, re-folded, and purified by gel filtration chromatography and C(4) RP-HPLC. Authentic rat BTC was obtained after proteolytic cleavage of the fusion protein with Factor Xa. Factor Xa cleaved an additional site within the BTC protein, generating a truncated isoform separable from full-length BTC by heparin-affinity chromatography. Recombinant rat BTC stimulated the proliferation of mouse Balb/c 3T3 fibroblasts and competed for binding to the ErbB1 receptor in a dose-dependent manner analogous to that of BTC purified from natural sources.

A Novel Inhibitory Effect on Prostacyclin Synthesis of Coupling Factor 6 Extracted from the Heart of Spontaneously Hypertensive Rats

The possible presence of an unknown prostacyclin synthesis inhibitory substance has been reported in some strains of rats. We purified the inhibitory substance from the heart of spontaneously hypertensive rats by collecting active fractions after gel-filtration column chromatography and two steps of reverse-phase high performance liquid chromatography. The amino acid composition and automated gas-phase sequencing of the full-length substance and fragments cleaved by AspN indicated that the prostacyclin-inhibitory peptide was identical to coupling factor 6. Recombinant rat coupling factor 6, which was synthesized using a cleavable fusion protein strategy, attenuated base-line and bradykinin (10(-6) M)-induced prostacyclin synthesis and [3H]arachidonic acid (AA) release in human umbilical vein endothelial cells in a dose-dependent manner (10(-9)-10(-7) M). Exogenous AA- and prostaglandin H2-induced prostacyclin synthesis were unchanged even after treatment with 10(-7) M recombinant coupling factor 6. Base-line and bradykinin-induced [3H]AA release were suppressed by arachidonyltrifluoromethyl ketone, a relatively specific inhibitor of cytosolic phospholipase A2 at 40 microM, and simultaneous administration of coupling factor 6 showed no further effect. Neither oleyloxyethyl phosphorylcholine at 1 microM nor bromoenol lactone at 1 microM affected AA release. Preincubation (1 min) with 10(-7) M recombinant coupling factor 6 had no influence on adenosine diphosphate- and collagen-induced platelet aggregations. We conclude that coupling factor 6 possesses a novel function of prostacyclin synthesis inhibition in endothelial cells via suppression of Ca2+-dependent cytosolic phospholipase A2, although it is unclear whether coupling factor 6 functions in normal conditions or only in pathophysiological states.

Cooperativity and Dimerization of Recombinant Human Estrogen Receptor Hormone-binding Domain

The estrogen receptor dimerizes and exhibits cooperative ligand binding as part of its normal functioning. Interaction of the estrogen receptor with its ligands is mediated by a C-terminal hormone-binding domain (HBD), and residues within the HBD are thought to contribute to dimerization. To examine dimer interactions in the isolated HBD, a human estrogen receptor HBD fragment was expressed in high yield as a cleavable fusion protein in Escherichia coli. The isolated HBD peptide exhibited affinity for estradiol, ligand discrimination, and cooperative estradiol binding (Hill coefficient approximately 1.6) similar to the full-length protein. Circular dichroism spectroscopy suggests that the HBD contains significant amounts of alpha-helix ( approximately 60%) and some beta-strand ( approximately 7%) and that ligand binding induces little change in secondary structure. HBD dimer dissociation, measured using size exclusion chromatography, exhibited a half-life of approximately 1.2 h, which ligand binding increased approximately 3-fold (estradiol) to approximately 4-fold (4-hydroxytamoxifen). These results suggest that the isolated estrogen receptor HBD dimerizes and undergoes conformational changes associated with cooperative ligand binding in a manner comparable to the full-length protein, and that one effect of ligand binding is to alter the receptor dimer dissociation kinetics.

Purification and Characterization of Human Pancreatic Polypeptide Expressed in E. coli

The region of cDNA encoding human pancreatic polypeptide (hPP) was obtained by polymerase chain reaction (PCR) and subcloned into an expression vector. The pancreatic polypeptide gene was expressed in Escherichia coli in two versions: as a cleavable fusion protein with IgG-binding synthetic ZZ domains of protein A from Staphylococcus aureus or with the 1-48 fragment of λ Cro repressor. Site-specific hydrolysis by hydroxylamine was used to cleave the fusion protein, releasing the human polypeptide. The structure of the obtained hPP has been studied by scanning microcalorimetry and circular dichroism spectrometry. It has been shown that hPP in solutions close to neutral has a compact and unique spatial structure with an extended hydrophobic core. This structure is stable at 20 °C and co-operatively breaks down upon heating from this temperature.

A Fast Method for Obtaining Highly Pure Recombinant Herpes Simplex Virus Type 1 Thymidine Kinase

Recombinant Herpes Simplex Virus Type 1 thymidine kinase (TK) was isolated in a fast and gentle two-step procedure from Escherichia coli as a thrombin cleavable fusion protein. The TK was expressed as an inducible glutathione S-acetyl transferase fusion protein and purified in a first step by glutathione affinity chromatography. Proteolytic cleavage of the column bound TK with thrombin led to a truncated enzyme, resulting from two new and hitherto unknown cleavage sites, determined by N-terminal sequencing. In a second step, the TK was further purified from the cleavage products by ATP affinity chromatography, yielding homogeneously pure TK as shown by SDS-PAGE and mass spectrometry. Both the fusion protein and the purified enzyme show enzymatic activity with the same Km value of 0.2 μM for the natural substrate thymidine. Determination of the native molecular weight indicated that the pure enzyme and the fusion protein are biologically active as homodimers. Therefore the recombinant enzyme has the same biochemical characteristics as the viral TK, expressed in infected cells.

22] Production of human hemoglobin in Escherichia coli using cleavable fusion protein expression vector

Publisher Summary This chapter discusses the production of human hemoglobin in Escherichia coli ( E. coli ) using cleavable fusion protein expression vector. The engineering of Hb is a powerful method of investigating various functional and structural aspects of Hb. This is the only method of making human hemoglobin in a microorganism until soluble and functional Hb is produced in E. coli. Hb made by this method has, at the N termini, an extra Met residue, which arises from the initiation AUG codon. The oxygen binding of this Hb is only slightly different from that of human hemoglobin A. The soluble and functional form of human hemoglobin is produced by coexpressing α- and β-globins in the yeast Saccharomyces cerevisiae. The N termini of both subunits were processed correctly and hence this is the first authentic functional Hb tetramer to be produced in a microorganism. Despite these developments, the method is valuable because it permits the preparation from E. coli of large amounts of Hb that is chemically identical to human Hb.

Expression and purification of active recombinant platelet factor 4 from a cleavable fusion protein

A synthetic gene for human platelet factor 4 (hPF4) has been expressed at high levels as a fusion protein in Escherichia coli. The hPF4 sequence has been cleaved from the fusion protein by cyanogen bromide treatment and purified by column chromatography. Like hPF4, our recombinant hPF4 (rhPF4) is tetrameric under physiological conditions, binds heparin, and inhibits angiogenesis. Extensive purification to remove trace amounts of uncleaved fusion protein completely from the desired product rhPF4 was difficult. We have exploited recombinant DNA technology by modifying the fusion moiety to accomplish separation. This type of modification, which did not affect expression level, could be applied to other recombinant fusion proteins.

Design, synthesis, and functional expression of a gene for charybdotoxin, a peptide blocker of K+ channels.

A gene encoding charybdotoxin (CTX), a K+ channel blocker from scorpion venom, was designed, synthesized, and expressed as a cleavable fusion protein in Escherichia coli. A sequence-specific protease, factor Xa, was used to cleave the fusion protein and thus release the toxin peptide. The recombinant toxin was purified, oxidized to form disulfide bonds, and treated to form N-terminal pyroglutamate. Recombinant CTX is identical to the native venom CTX with respect to high-performance liquid chromatography mobility, amino acid composition, and N-terminal modification. With single Ca2(+)-activated K+ channels as an assay system, recombinant CTX shows blocking and dissociation kinetics identical to the native venom toxin. The synthetic gene and high-level expression of functionally active CTX make it possible to study the fundamental mechanism of the toxin-ion channel interaction.

Production of a site specifically cleavable P-glycoprotein-.BETA.-galactosidase fusion protein.

We have fused full length and the carboxyl-half of human MDR1 cDNA with the E. coli lacZ gene via a collagen linker and allowed their expression in yeast Saccharomyces cerevisiae. Using antibodies against beta-galactosidase we partially purified the fusion proteins by immunoprecipitation and show here that the full length fusion protein has ATPase activity. By contrast, the fusion protein containing the carboxyl-half of P-glycoprotein did not show ATPase activity, indicating that both domains of P-glycoprotein are necessary. By treatment of the immunoprecipitated fusion protein with collagenase, P-glycoprotein was released from the beta-galactosidase moiety. The results shown here open the possibility for a large scale purification of P-glycoprotein using this site specifically cleavable fusion protein.