Characterization of recombinant human insulin-like growth factor binding proteins 4, 5, and 6 produced in yeast.

The insulin-like growth factor binding protein (IGFBP) family comprises six structurally distinct, but highly homologous proteins. They have been identified in serum and other biological fluids, tissue extracts, and cell culture media. We have recently cloned cDNAs encoding human IGFBP-4, -5, and -6 and have now expressed these BPs in yeast as ubiquitin (Ub)-IGFBP fusion proteins. Western ligand blotting with 125I-IGF II under nonreducing conditions of recombinant human (rh) IGFBP-containing yeast lysates revealed specific binding bands for IGFBP-4, -5, and -6 at apparent molecular masses of 24-26, 30-32, and 24-26 kDa, respectively, indicating processing of the fusion proteins. High-performance liquid chromatography-purified rhIGFBPs had virually the same amino acid composition, amino acid number, and NH2-terminal sequences as the native BPs. Except for the affinity of rhIGFBP-6 for IGF I (Ka = 8.5 x 10(8) M-1), the affinity constants of the three IGFBPs for IGF I and II lie between 1.7 and 3.3 x 10(10) M-1, i.e. 25-100 times higher than the IGF I and II affinities of the type I IGF receptor. When present in excess, rhIGFBP-4, -5, and -6 inhibited IGF I- and II-stimulated DNA and glycogen synthesis in human osteoblastic cells, but rhIGFBP-6 had only a weak inhibitory effect on IGF I in agreement with its relatively lower IGF I affinity constant. The results of this study show that the primary effect of the three rhIGFBPs is the attenuation of IGF activity and suggest that IGFBPs contribute to the control of IGF-mediated cell growth and metabolism.     

重组人表皮生长因子的稳定性

考察了不同条件下重组人表皮生长因子（rhEGF）的稳定性。结果表明,不同的保存条件（物理状态、温度、pH、浓度等）对rhEGF的稳定性有显影响,使用适当的添加剂（保护剂、抗氧剂、抑菌等）可以提高rhEGF的稳定性。上述结果为rhEGF的制剂学研究提供了依据。     

Rapid purification and partial characterization of recombinant human epidermal growth factor produced by Escherichia coli

Human recombinant EGF, secreted into the extracellular medium by E. coli cells, was purified by a combination of solid phase extraction and HPLC. Using these techniques, the peptide was purified 122-fold, with a recovery of greater than 75%. The purified hEGF manifested no contaminating protein bands on electrophoretic gels. Amino acid analysis of the purified peptide was identical to that of authentic hEGF.     

Purification of recombinant human epidermal growth factor secreted from the methylotrophic yeast Hansenula polymorpha.

The gene encoding human epidermal growth factor (hEGF) was expressed as a fusion protein with the Saccharomyces cerevisiae-derived prepro alpha-factor leader in the methylotrophic yeast Hansenula polymorpha. The recombinant hEGF(1-53), when secreted by H. polymorpha, rapidly cleaved to hEGF(1-52) by carboxy-terminal proteolysis, resulting in the accumulation of C-terminal-truncated hEGF(1-52) in the culture medium. To solve this problem, we constructed a H. polymorpha mutant in which the KEX1 gene coding for carboxypeptidase ysc(alpha) was disrupted. The extent of C-terminal proteolysis of hEGF was significantly reduced when this kex1 disruptant was used as a host strain. After 24 h of shake-flask culture, most of the hEGF secreted by the kex1 disruptant remained intact, whereas more than 90% of the hEGF secreted by the wild-type was C-terminally cleaved. The recombinant hEGF was purified to >98% purity by two sequential steps of preparative scale anion exchange chromatography and reverse-phase HPLC. The authenticity of purified hEGF was confirmed by HPLC, N-terminal amino acid sequencing, and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy analyses.     

Characterization of recombinant human granulocyte-colony-stimulating factor produced in mouse cells.

Mouse C127I cells were transformed with a chimeric plasmid consisting of bovine papillomavirus DNA and human granulocyte-colony-stimulating factor (G-CSF) cDNA placed under the control of the SV40 early promoter. The transformed cells secreted constitutively a high level of human G-CSF, 10-20 micrograms/ml in a low-serum medium. The secreted G-CSF has been purified to homogeneity by a two-step procedure including gel filtration and hydrophobic column chromatography. The purified recombinant G-CSF runs as a single band with an apparent Mr of 19,000 on a polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. This value corresponds to that of the native human G-CSF purified from the medium conditioned by human carcinoma CHU-2 cells. The recombinant human G-CSF was as active as native G-CSF in vitro in supporting proliferation of mouse NFS-60 cells and stimulating colony formation from human as well as mouse bone marrow cells. When the recombinant human G-CSF was subcutaneously administrated into mice, a remarkable stimulation of granulopoiesis and splenomegaly was observed.     

Characterization of the N-oligosaccharides attached to the atypical Asn-X-Cys sequence of recombinant human epidermal growth factor receptor

The extracellular domain of human EGF receptor (sEGFR) produced by CHO cells has been used in various biophysical studies to elucidate the molecular mechanism of EGF-induced receptor activation. We have found that the CHO sEGFR contains one oligosaccharide chain attached to an atypical N-glycosylation consensus sequence, Asn(32 )-X( 33 )-Cys(34 ). The oligosaccharide structure at Asn(32 ) is a mixture of the monosialo and asialo forms of a core fucosylated biantennary complex-type oligosaccharide. Deletion of this atypical glycosylation site by replacement of Asn(32 ) with lysine changed neither the expression nor function of the full length EGFR in CHO cells. The glycosylation at Asn(32 ) in CHO sEGFR was incomplete: 20% of Asn(32 ) remained unmodified. Thus, CHO sEGFR itself is heterogeneous with respect to the glycosylation at Asn(32 ), which may cause problems in biophysical studies. An attempt to remove the oligosaccharide at Asn(32 ) enzymatically did not succeed under nondenaturing conditions. Therefore, sEGFR with the mutation of Asn(32) -> Lys(32 )is useful for biophysical and biochemical studies, and, particularly, for X-ray crystallography.     

Incomplete process of recombinant human platelet-derived growth factor produced in yeast and its effect on the biological activity.

Partially purified recombinant human Platelet-derived Growth Factor BB homodimer isolated from yeast culture media contains variable amounts of unprocessed PDGF-BB. This unprocessed PDGF-BB is found as a result of incomplete cleavage of the precursor to form the mature protein. Although the signal peptide is efficiently removed, a fraction of the PDGF secreted has an extended sequence corresponding to the truncated yeast alpha-factor leader. The data suggest that it is the amino acid chain from the truncated a-factor leader and not the sugar moiety attached to it that is responsible for the higher mitogenic activity found in this unprocessed molecule compared to highly purified PDGF-BB.     

Circular dichroism of reduced and oxidized recombinant human epidermal growth factor.

To further elucidate the role of the disulfide bonds in determining the protein folding of recombinant human epidermal growth factor (r-HuEGF) we studied the structure of reduced and oxidized r-HuEGF using circular dichroism (CD). The far UV CD spectrum of reduced r-HuEGF in 10 mM sodium phosphate pH 3.0 is very different from that of the oxidized molecule. The spectrum of the reduced molecule consists of a plateau from 225 to 200 nm, consistent with the presence of alpha-helix, beta-sheet, and unordered structure. The addition of the alpha-helix inducer trifluoroethanol to the reduced molecule resulted in an enhancement of alpha-helix, at the apparent expense of beta-sheet, while the oxidized molecule was unaffected by the presence of this reagent. Secondary structure predictions based on the amino acid sequence of EGF correlate most closely with the structure of the reduced molecule. From these results, it appears that the r-HuEGF has a more regular secondary structure in the absence of the disulfide bonds than in their presence. This suggests that the folding of EGF occurs by destroying the regular secondary structure that was present in the reduced state, and that the structure of the native molecule is dictated largely by disulfide bonding.     

Stabilization of a recombinant human epidermal growth factor parenteral formulation through freeze-drying

Development studies were performed to design a pharmaceutical composition that allows the stabilization of a parenteral rhEGF formulation in a lyophilized dosage form. Unannealed and annealed drying protocols were tested for excipients screening. Freeze-dry microscopy was used as criterion for excipients and formulation selection; as well as to define freeze-drying parameters. Excipients screening were evaluated through their effect on freeze-drying recovery and dried product stability at 50 °C by using a comprehensive set of analytical techniques assessing the chemical stability, protein conformation and bioactivity. The highest stability of rhEGF during freeze-drying was achieved by the addition of sucrose or trehalose. After storing the dried product at 50 °C, the highest stability was achieved by the addition of dextran, sucrose, trehalose or raffinose. The selected formulation mixture of sucrose and dextran could prevent protein degradation during the freeze-drying and delivery processes. The degradation rate assessed by RP-HPLC could decrease 100 times at 37 °C and 70 times at 50 °C in dried with respect to aqueous formulation. These results indicate that the freeze-dried formulation represents an appropriate technical solution for stabilizing rhEGF.     

Characterization of human epidermal growth factor in human serum and urine under native conditions

The objective of this study was to investigate the molecular nature of the human epidermal growth factor (EGF) in serum and urine samples of normal subjects. Recombinant EGF emerged as a single peak and did not interact with human IgG1 and albumin up to the concentration of 12 microg/ml. Freshly separated human serum contained only trace amounts of EGF. However, EGF appeared and increased in serum separated from blood after spontaneous overnight clotting. The authentic 6 kDa form of EGF made up nearly 40% of the total EGF in serum and revealed relatively homogeneous feature. The remaining immunoreactive fractions corresponded to 160 kDa proEGF. Immunoreactive EGF in blood seemed to be associated with the EGF release from platelets. TSKgel G3000SW chromatography of freshly-voided morning and day urines revealed that urine samples mainly contained two major form of EGF; a high-molecular-weight (HMW) and low-molecular-weight (LMW) forms. In the sense of molecular nature of EGF contents, morning urine was more heterogeneous than day urine of the same individuals. The LMW form of EGF in morning urine, in which its proportion was more than 90% of the total EGF, revealed further heterogeneous feature generally containing three to four different components.     

Expression line approach to recombinant human epidermal growth factor into the yeast,Pichia pastoris from Huh-7 cell line

Beta-urogastrone also known as human epidermal growth factor is a key member of epidermal growth factor family having role in cell proliferation and differentiation in vivo as well as in vitro. Human epidermal growth factor gene has been isolated from different tissues but the method of isolation is technically difficult and complicated as it deals with biopsies. Here we isolated mature partial human epidermal growth factor gene from Huh-7 cell line, amplified and abridged toward mature coding region with three steps PCR, sequenced for homology with wild type human epidermal growth factor gene, inbuilt with sites of interest and cloned in Pichia pastoris for expression study. Isolated mature human epidermal growth factor gene from Huh-7 cell line showed 100 % sequence homology to wild type human epidermal growth factor gene and gives the native expression for human epidermal growth factor peptide. In this study we report that Huh-7 cell line is an easy source for the particular gene of human epidermal growth factor isolation and we are also suggesting P. pastoris is an expression system to produce recombinant human epidermal growth factor of the therapeutic importance resembling to the natural human system.     

Characterization of recombinant human factor VIII

Recently, complete human factor VIII DNA clones have been obtained and subsequently expressed in baby hamster kidney cells (Wood, W. I., Capon, D. J., Simonsen, C. C., Eaton, D. L., Gitschier, J., Keyt, B., Seeburg, P. H., Smith, D. H., Hollingshead, P., Wion, K. L., Delwart, E., Tuddenham, E. G. D., Vehar, G. A., and Lawn, R. M. (1984) Nature 312, 330-337). The recombinant factor VIII (rVIII) protein secreted from these cells has now been purified allowing its structural analysis and comparison to plasma-derived factor VIII (pdVIII). Analysis of purified rVIII by sodium dodecyl sulfate-polyacrylamide gel electrophoresis shows that it consists of multiple polypeptides with relative mobilities (Mr) ranging from 80,000-210,000. The same pattern of polypeptides is also observed for pdVIII resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The proteins associated with rVIII are recognized by pdVIII antibodies in a Western blot. When rVIII and pdVIII are subjected to isoelectric focusing they are resolved into a similar pattern of protein bands. Thrombin, factor Xa, and activated protein C, which modulate factor VIII activity by proteolysis, process rVIII in the same manner they do pdVIII. As is the case for pdVIII, thrombin activation of rVIII coagulant activity correlates with the generation of subunits with Mr of 73,000, 50,000 and 43,000. These subunits appear to form a metal-(perhaps Ca2+) linked complex. EDTA inactivates thrombin-activated rVIII and pdVIII, with the activity being regenerated after the addition of a molar excess of MnCl2. The results suggest that rVIII is structurally and functionally very similar to pdVIII.     

Expression of recombinant epidermal growth factor inE. coli

Epidermal growth factor (EGF) known as a urgastrone is a powerful mitogen with a wide variety of possibilities for medical usages. A mature EGF coding region was isolated from human prepro-EGF sequence by a conventional PCR and cloned into pQE vector in which the gene product was supposed to be expressed with 6×His tag for the subsequent purification. The recombinant mature EGF was expressed in M15[Rep4], anEscherichia coli host strain, in amount of 30–40% of total proteins present inE. coli extract by the addition of isopropylthio-β-galactopyranoside (IPTG). The recombinant EGF purified using a Ni²⁺-NTA affinity column chromatography was active in its ability to induce phosphorylation on tyrosine residues of several substrate proteins when murine NIH3T3 and human MRC-5 fibroblast cells were stimulated with it. This work may provide the basic technology and information for the production of recombinant EGF.     

Expression, purification and characterization of recombinant human insulin-like growth factor I in yeast

Insulin-like growth factor I (IGF-I) is a 70 amino acid (aa) protein that is structurally similar and functionally related to insulin. We have inserted a synthetic gene coding for human IGF-I into a Saccharomyces cerevisiae expression vector utilizing the MF alpha 1 promoter and pre-pro leader peptide. This vector directs the expression and secretion of native, biologically active growth factor. Cleavage of the pre-pro alpha factor leader sequence in vivo results in the secretion of a 70-aa recombinant IGF-I molecule with the native N-terminal glycine residue. Human IGF-I purified from yeast culture supernatant is equipotent to serum-derived IGF-I in inhibiting [125I]IGF-I binding to type-I IGF receptors and crude human serum-binding proteins. Recombinant IGF-I is also equipotent to human IGF-I in the stimulation of DNA synthesis in rat aortic smooth-muscle cells. In contrast, yeast recombinant IGF-I is less potent than serum-derived IGF-I in binding to type-2 IGF receptors. The ability to produce native, biologically active IGF-I in yeast will allow the elucidation of binding domains through the expression and characterization of specific structural analogs.     

Characterization of gingival epithelium epidermal growth factor receptor

The binding characteristics of gingival epithelium epidermal growth factor (EGF) receptor were investigated using epithelial cell membranes from bovine gingiva. The binding of [125I]EGF was found to be time and protein concentration dependent, reversible, and specific. Unlabeled EGF competed for [125I]EGF binding with IC50 of 0.25nM and maximum displacement of 93% at 0.81nM. Scatchard analysis of the binding data inferred the presence of two binding sites, one of high affinity (Kd = 3.3 nM and Bmax = 47.3fmol/mg protein) and the other of a low affinity (Kd = 1.6 microM and Bmax = 1.9pmol/mg protein). Crosslinking of [125I]EGF to gingival membranes followed by polyacrylamide gel electrophoresis and autoradiography revealed a receptor protein of 170kDa.     

Mass production of human epidermal growth factor using fed-batch cultures of recombinant Escherichia coli

Fed-batch cultures of recombinant E. coli HB101 harboring expression plasmid pTRLBT1 or pTREBT1, with acetate concentration monitoring, are investigated to obtain high cell density and large amounts of human epidermal growth factor (hEGF). The expression plasmid pTRlBT1 contains a synthetic hEGF gene attached downstream of the N-terminal fragment of the trp L gene preceded by the trp promoter. The expression plasmid pTREBT1 contains the same coding sequence attached downstream of the N-terminal fragment of the trp E gene preceded by the trp promoter, trp L gene, and attenuator region. E. coli harboring pTREBT1 produces 0.56 mg/L hEGE and immediately degrades it. On the other hand E. coli harboring pTRLBT1 produces 6.8 mg/L hEGF and does not decompose it. Prominent inclusion bodies are observed in E. coli cells harboring pTRLBT1 using an election microscope. To Cultivate E. coli harboring pTRLBT1, a fed-batch culture system, divided into a cell growth step and an hEGF production step, is carried out. The cells grow smoothly without acetate-induced inhibition. Cell concentration and hEGF quantity reach the high values of 21 g/L and 60 mg/L, respectively.     

人表皮生长因子的研究进展

人表皮生长因子是激活表皮生长因子受体的生长因子家族的典型成员,由人体的多个组织器官合成与分泌,通过结合受体激活一系列信号途径,调控细胞的增殖、分化和迁移等。近年来,有关人表皮生长因子的研究已扩展到其在人类生理和病理作用的领域,尤其在组织再生和伤口愈合方面成为研究热点。文中综述了人表皮生长因子的研究进展,简要描述了其基因和蛋白的结构与特点、作用机制与生物学效应,重点介绍该生长因子在胃肠溃疡愈合、皮肤伤口修复和肿瘤病理过程中的作用与影响,从而为相关研究提供辅助信息。     

Secretion of recombinant human epidermal growth factor into the periplasm in Escherichia coli cells]

Secretion vectors were constructed in which a synthetic gene of human epidermal growth factor (hEGF) joined with a gene coding for the leader peptide to one of the E. coli outer membrane major proteins (OmpF) is controlled by tac promoter. The increase of the hEGF yield was achieved by the multiplication of the gene copies. The hEGF in bacterial cells was secreted into periplasm. The recombinant protein was isolated by means of reverse phase chromatography as almost homogenous preparation (greater than 98%), the yield being 7 mg/l bacterial culture. The sequence of twenty-five N-terminal amino acid residues of the isolated hEGF coincided with that of the natural protein. The preparation proved to be biologically active.     

Characterization of a cysteine-free analog of recombinant human basic fibroblast growth factor

Using oligo site-directed mutagenesis, we have modified our synthetic gene for human basic fibroblast growth factor (bFGF) to replace all four cysteine codons with serine codons. The corresponding protein was expressed in Escherichia coli and purified from inclusion bodies by solubilization in urea followed by a series of column chromatographies and a folding step. The resulting protein, having no cysteine residues, is unable to form either intramolecular or intermolecular disulfide bonds. The secondary and tertiary structures of the purified analog, as determined by circular dichroism and fluorescence spectroscopy, were identical within experimental error to recombinant bovine and human bFGF with unaltered amino acid sequences. Reflecting the similar conformation, the analog protein exhibited mitogenic activity on NIH 3T3 cells which was indistinguishable from the natural sequence molecule.     

Extracellular production of recombinant human epidermal growth factor (hEGF) in Escherichia coli cells

An expression plasmid pPTK-hEGF2 was constructed to provide for the extracellular production of recombinant human epidermal growth factor by the Escherichia coli cells. The plasmid contained two expression cassettes, one of which carried a tandem of the fused genes ompF-hegf under the control of the tac promoter, ensuring regulated secretion of hEGF into the E. coli periplasm, and another one contained the kil gene from the ColE1 plasmid under the control of lac promoter. The regulated low-level biosynthesis of Kil protein increased the permeability of E. coli outer membrane for periplasmic proteins. This enabled the recombinant proteins secreted into the cell periplasm to outflow into the cultural medium. As a result, the E. coli strains that harboured this plasmid construct produced effectively the recombinant hEGF into the cultural medium. The yields of hEGF produced by the nTG1(pPTK-hEGF2) and HB101(pPTK-hEGF2) strains reached 25 and 30 mg/l of cell culture after 14 and 18 h of cultivation, respectively. The hEGF preparation isolated possessed biological activity both in vivo and in vitro.