Synthesis of a gene for human growth hormone and its expression in Escherichia coli

Structural and functional characterization of recombinant human growth hormone isolated from transgenic pig milk

This study aimed to establish and reproduce transgenic pigs expressing human growth hormone (hGH) in their milk. We also aimed to purify hGH from the milk, to characterize the purified protein, and to assess the potential of our model for mass production of therapeutic proteins using transgenic techniques. Using ~15.5 L transgenic pig milk, we obtained proteins with ≥ 99% purity after three pre-treatments and five column chromatography steps. To confirm the biosimilarity of our milk-derived purified recombinant hGH (CGH942) with commercially available somatropin (Genotropin), we performed spectroscopy, structural, and biological analyses. We observed no difference between the purified protein and Genotropin samples. Furthermore, rat models were used to assess growth promotion potential. Our results indicate that CGH942 promotes growth, by increasing bone development and body weight. Toxicity assessments revealed no abnormal findings after 4 weeks of continuous administration and 2 weeks of recovery. The no-observed-adverse-effect level for both males and females was determined to be 0.6 mg/kg/day. Thus, no toxicological differences were observed between commercially available somatropin and CGH942 obtained from transgenic pig milk. In conclusion, we describe a transgenic technique using pigs, providing a new platform to produce human therapeutic proteins.

High level expression of recombinant human growth hormone in Escherichia coli: crucial role of translation initiation region

For high-throughput production of recombinant protein in Escherichia coli (E. coli), besides important parameters such as efficient vector with strong promoter and compatible host, other important issues including codon usage, rare codons, and GC content specially at N-terminal region should be considered. In the current study, the effect of decreasing the percentage of GC nucleotides and optimizing codon usage at N-terminal region of human growth hormone (hGH) cDNA on the level of its expression in E. coli were investigated. Mutation in cDNA of hGH was performed through site-directed mutagenesis using PCR. Then, the mutant genes were amplified and cloned into the expression vector, pET-28a. The new constructs were transformed into the BL21(DE3) strain of E. coli and chemically induced for hGH expression. At the final stage, expressed proteins were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), scanning gel densitometry, and western blot. SDS-PAGE scanning gel densitometry assay and western blot analysis revealed higher expression level of hGH by using the two new expressions constructs (mutant genes vectors with decreasing GC content and optimized-codon usage at N-terminal of cDNA) in comparison with wild gene expression vector. Obtained results demonstrated that decreasing the GC nucleotide content and optimization of codon usage at N-terminal of the hGH cDNA could significantly enhance the expression of the target protein in E. coli. Our results highlight the important role of both 5´ region of the heterologous genes in terms of codon usage and also GC content on non-host protein expression in E. coli.

Preparation of soluble isotopically labeled human growth hormone produced in Escherichia coli

Isotopically labeled proteins have been used as internal standards for mass spectrometry (MS)-based absolute protein quantification. Although this approach can provide highly accurate analyses of proteins of interest within a complex mixture, one of the major limitations of this method is the difficulty in preparing uniformly labeled standards. Human growth hormone (hGH) is one of the most important hormones that circulate throughout the body, and its measurement is primarily of interest in the diagnosis and treatment of growth disorders. In order to provide a useful internal standard for MS-based hGH measurement, we describe an efficient strategy to produce a potentially valuable, stable isotope-labeled hGH with high purity and yield. The strategy involves the following steps: solubilization of hGH under labeling conditions, detection of stable isotope incorporation, large-scale purification, analysis of the labeled protein, and assessment of the labeling efficiency. We show that the yield of soluble hGH under selective isotopic labeling conditions can be greatly increased by optimizing protein expression and extraction. Our efficient method for generating isotopically labeled hGH does not influence the structural integrity of hGH. Finally, we assessed the efficiency of stable isotope labeling at the intact protein level, and the result was further verified by amino acid analysis. These results clearly indicate that our labeling approach allows an almost complete incorporation of ¹³C₆¹⁵N₄-arginine into the hGH expressed in E.coli without detectable isotope scrambling.

Use of Ubp1 protease analog to produce recombinant human growth hormone in Escherichia coli

Background

Numerous bacterial human growth hormone (hGH) expression methods under conventional fermentation and induction conditions have been described. Despite significant progress made in this area over the past several years, production of recombinant hGH by using cellular expression systems still requires further optimization. Fusion of the ubiquitin (Ub) tag to the hGH protein allowed to increase of the overall efficiency of the biosynthesis and improve the protein stability. Ub is a protein composed of 76 amino acid residues with a molecular mass of 8.6 kDa, expressed in all eukaryotes. This protein is an element of the universal protein modification system, which does not occur in bacteria, and is a useful carrier for heterologous proteins obtained through expression in Escherichia coli. Purification of Ub-fusion proteins is easier than that of unconjugated recombinant proteins, and Ub can be removed by deubiquitinating proteases (DUBs or UBPs).

Results and Conclusion

In the present study the UBPD2C protease, a stable UBP1 analog, was produced as a recombinant protein in E. coli and used for production of recombinant human growth hormone (rhGH). hGH was expressed as a fusion protein with Ub as a tag. Our findings show that the UBPD2C protease is very effective in removing the Ub moiety from recombinant Ub-fused hGH. The described approach enables obtaining a considerable yield of rhGH in a purity required for pharmaceutical products.

Recombinant approach for the production of HIV fusion inhibitor Enfuvirtide using Escherichia coli

The use of antiretroviral drugs is gaining importance in the recent past for the treatment of human immunodeficiency virus infection. Enfuvirtide (T20) is one of the fusion inhibitors, inhibits the fusion between the virus and healthy target CD4 cells. The treatment with T20 involves very high therapeutic dose. In addition to its high dose, production of T20 by synthetic methods is expensive and cumbersome. We report an alternative recombinant approach for the production of the T20 peptide through a novel short fusion-tag expression system. This expression system consists of the hydrophobic region of growth hormone (GH) as the fusion tag, a factor Xa cleavage site upstream to the T20. The fusion protein was expressed in Escherichia coli as inclusion bodies. We also report here, a simple and an efficient down-stream strategy for the purification of recombinant T20 peptide (rT20). Our study is the first to demonstrate a novel approach using GH fusion tag, ensured the peptide stability, for the production of rT20 which yields more than 250mg/L with 98% purity. The biological activity of the rT20 is comparable to its synthetic counterpart. Thus, this novel approach could be an alternate method of choice for production of therapeutically important small peptides.

Complete solubilization and purification of recombinant human growth hormone produced in Escherichia coli

High-level expression of recombinant human growth hormone (hGH) in Escherichia coli (E. coli) leads to the formation of insoluble aggregates as inclusion bodies devoid of biological activity. Until recently, significant efforts have been made to improve the recovery of active hGH from inclusion bodies. Here, we developed an efficient procedure for the production of completely soluble hGH by minimizing the formation of inclusion bodies and optimizing protein purification conditions. Under the newly established conditions we were able to obtain most of the total hGH in the soluble fraction. We show that the soluble protein can be efficiently purified in high yield by a series of chromatographic procedures. We analyzed the resulting hGH using various analytical techniques such as reversed-phase high-performance liquid chromatography (RP-HPLC), size-exclusion chromatography (SEC), matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and circular dichroism (CD). These multiple analyses support the conclusion that we obtained highly pure hGH with the expected molecular mass and intact secondary structure. The biological activity of purified hGH was also confirmed by evaluating its growth-promoting effect using a cell proliferation assay. Taken together, we describe a straightforward strategy for the production of completely soluble and biologically active hGH in E. coli.

Discrimination of recombinant from natural human growth hormone using DNA aptamers

Detection of athletes who use synthetic human growth hormone (hGH; or somatotropin) to enhance physical strength and obtain an advantage in competitive sports is a formidable problem, as rhGH is virtually identical to the natural pituitary hormone. However, some post-translational and other modifications have been documented by chromatographic separation and mass spectrometry (MS) in a small percentage of rhGH. In the present work, development of DNA aptamers against research-grade rhGH and natural hGH with adsorption of the rhGH aptamers against natural hGH was shown to produce a small family of aptamer sequences that bound consistently with greater affinity to rhGH over a low nanogram-to-microgram range in ELISA-like microplate assays. This collection of rhGH discriminatory aptamer sequences shared some short sequence segments and secondary structural features. The top rhGH discriminatory aptamers also appeared to cross-react with human myoglobin and BSA but not with bone collagen peptides and an unrelated viral envelope peptide. The cross-reactivity results suggested several strings of up to five consecutive amino acids that might serve as common epitopes for aptamer binding. SDS-PAGE revealed that the rhGH existed largely as a 45-kDa dimer, and the natural hGH was almost exclusively monomeric. The existence of the rhGH dimer suggests that a discontinuous "bridge" epitope may exist on the rhGH, which spans the subunits, thereby accounting somewhat for the difference in detection. Overall, these results suggest that aptamers might be useful for routine, presumptive laboratory screening to identify athletes who are potentially cheating by administration of rhGH.

Large-scale production of major house dust mite allergen der f 2 mutant (C8/119S) in Escherichia coli

Hyposensitization, in which causative antigens of allergic diseases are injected, is the sole means of a radical cure for allergic diseases. Since the therapeutic allergens currently used are naturally extracted, producing preparations with a stable titer from such extracts is extremely difficult. There are several reports on the expression of recombinant mite allergens in Escherichia coli using inducers. The use of an inducer for industrial production will lead to high costs and, for therapeutic use, it must be removed in the purification process. C8/119S is a mutant of Der f 2, a major house dust mite allergen. The C8/119S gene was integrated downstream of the trp promoter to produce the expression plasmid (pWU11-C8/119S). Then, this expression plasmid was used to transform E. coli strain HB101 (pWU11-C8/119S/HB101). A recombinant E. coli pWU11-C8/119S/HB101 did not express C8/119S in a low-temperature culture (32 degrees C), but C8/119S was induced to a high level of expression in a high-temperature culture (37 degrees C). pWU11-C8/119S/HB101 proliferated when expression was induced by high temperature and an approximately 3-fold greater proliferation was obtained compared with the use of an inducer in a large-scale culture. The C8/119S protein was expressed as inclusion bodies and obtained by refolding and chromatography purifications. The immunological properties of C8/119S were assessed by western blotting. Western blotting demonstrated that purified C8/119S reacted with a monoclonal anti-Der f 2 antibody (18G8). pWU11-C8/119S/HB101 can be used as an easy, low cost expression system on a large scale. It is also advantageous for industrial production in that the addition of an inducer is not required to achieve expression of the mite allergen.

Neuroendocrine hormones such as growth hormone and prolactin are integral members of the immunological cytokine network

Neuroendocrine hormones such as growth hormone (GH) and prolactin (PRL) have been demonstrated to accelerate the recovery of the immune response after chemotherapy and bone marrow transplantation and to enhance the restoration of immunity in individuals infected with HIV and in normal individuals with compromised immune systems associated with aging. As the mechanism of action of these hormones has been elucidated, it has become clear that they are integral members of the immunological cytokine/chemokine network and share regulatory mechanisms with a wide variety of cytokines and chemokines. The members of this cytokine network induce and can be regulated by members of the suppressor of cytokine signaling (SOCS) family of intracellular proteins. In order to take advantage of the potential beneficial effects of hormones such as GH or PRL, it is essential to take into consideration the overall cytokine network and the regulatory effects of SOCS proteins.

A ferredoxin Arg-Glu pair important for efficient electron transfer between ferredoxin and ferredoxin-NADP(+) reductase

In order to elucidate the importance of a ferredoxin (Fd) Arg-Glu pair involved in dynamic exchange from intra- to intermolecular salt bridges upon complex formation with ferredoxin-NADP(+) oxidoreductase (FNR), Equisetum arvense FdI and FdII were investigated as normal and the pair-lacking Fd, respectively. The FdI mutant lacking this pair was unstable and rapidly lost the [2Fe-2S] cluster. The catalytic constant (k(cat)) of the electron transfer for FdI is 5.5 times that for FdII and the introduction of this pair into FdII resulted in the increase of k(cat) to a level comparable to that for FdI, demonstrating directly that the Arg-Glu pair is important for efficient electron transfer between Fd and FNR.

Synthesis and chromatographic purification of recombinant human pituitary hormones

Recombinant DNA-derived proteins and, in particular, human pituitary hormones, are increasingly used for research, diagnostic and therapeutic purposes. This trend has demanded new synthetic approaches and improved purification techniques. The type and sequence of the purification steps have to be selected in accordance with the cloning and protein expression strategy, the host organism and cellular localization of the protein of interest, with a view to producing the desired product at a required purity, biological activity and acceptable cost. This review article describes and analyzes the main synthetic and purification strategies that have been used for the production of recombinant human growth hormone, prolactin, thyrotropin, luteinizing hormone and follicle-stimulating hormone, giving special consideration to the few published downstream processes utilized by the biotechnology industry. Practically all types of prokaryotic and eukaryotic organisms utilized for this purpose are also reviewed.

The 109 residue nerve tissue minihemoglobin from Cerebratulus lacteus highlights striking structural plasticity of the alpha-helical globin fold

A very short hemoglobin (CerHb; 109 amino acids) binds O(2) cooperatively in the nerve tissue of the nemertean worm Cerebratulus lacteus to sustain neural activity during anoxia. Sequence analysis suggests that CerHb tertiary structure may be unique among the known globin fold evolutionary variants. The X-ray structure of oxygenated CerHb (R factor 15.3%, at 1.5 A resolution) displays deletion of the globin N-terminal A helix, an extended GH region, a very short H helix, and heme solvent shielding based on specific aromatic residues. The heme-bound O(2) is stabilized by hydrogen bonds to the distal TyrB10-GlnE7 pair. Ligand access to heme may take place through a wide protein matrix tunnel connecting the distal site to a surface cleft located between the E and H helices.

Secretory leukoprotease inhibitor augments hepatocyte growth factor production in human lung fibroblasts

Secretory leukoprotease inhibitor (SLPI), an 11.7-kD nonglycosylated serine protease inhibitor, is produced and released into the fluids of mucosal surfaces including human lung. It comprises two domains with homologous amino acid sequences: the N-terminal domain possessing antibacterial activity, and the C-terminal domain with antiprotease activity. Here we report the positive regulation of hepatocyte growth factor (HGF) production in human lung fibroblasts exerted by SLPI or its C-terminal domain under physiologic concentrations (1 to 10 microM). This HGF production by SLPI was unaffected by the addition of interleukin (IL)-1 receptor antagonist. In contrast, human skin fibroblasts exerted no SLPI-stimulated increase in HGF production, despite the fact that IL-1beta increased HGF production with an intensity similar to that of human lung fibroblasts. Both the time-course and dose-response studies in human lung fibroblasts revealed that the induction of HGF messenger RNA (mRNA) and protein occurred in parallel, indicating that the mechanism existed at the steady-state mRNA level. A synthetic elastase inhibitor failed to induce HGF, but alpha(1)-antitrypsin also stimulated HGF production in lung fibroblasts. Inactivation of the antiprotease activity of SLPI or its C-terminal domain by an oxidizing agent (N-chlorosuccinimide) abolished their stimulatory effect on HGF production. These findings demonstrate that SLPI exerts a novel HGF induction and functions as an anti-inflammatory and regenerative factor in addition to its role in protease inhibition.

A novel two-over-two alpha-helical sandwich fold is characteristic of the truncated hemoglobin family

Small hemoproteins displaying amino acid sequences 20-40 residues shorter than (non-)vertebrate hemoglobins (Hbs) have recently been identified in several pathogenic and non-pathogenic unicellular organisms, and named 'truncated hemoglobins' (trHbs). They have been proposed to be involved not only in oxygen transport but also in other biological functions, such as protection against reactive nitrogen species, photosynthesis or to act as terminal oxidases. Crystal structures of trHbs from the ciliated protozoan Paramecium caudatum and the green unicellular alga Chlamydomonas eugametos show that the tertiary structure of both proteins is based on a 'two-over-two' alpha-helical sandwich, reflecting an unprecedented editing of the classical 'three-over-three' alpha-helical globin fold. Based on specific Gly-Gly motifs the tertiary structure accommodates the deletion of the N-terminal A-helix and replacement of the crucial heme-binding F-helix with an extended polypeptide loop. Additionally, concerted structural modifications allow burying of the heme group and define the distal site, which hosts a TyrB10, GlnE7 residue pair. A set of structural and amino acid sequence consensus rules for stabilizing the fold and the bound heme in the trHbs homology subfamily is deduced.

Refolding of therapeutic proteins produced in Escherichia coli as inclusion bodies

Overexpression of cloned or synthetic genes in Escherichia coli often results in the formation of insoluble protein inclusion bodies. Within the last decade, specific methods and strategies have been developed for preparing active recombinant proteins from these inclusion bodies. Usually, the inclusion bodies can be separated easily from other cell components by centrifugation, solubilized by denaturants such as guanidine hydrochloride (Gdn-HCl) or urea, and then renatured through a refolding process such as dilution or dialysis. Recent improvements in renaturation procedures have included the inhibition of aggregation during refolding by application of low molecular weight additives and matrix-bound renaturation. These methods have made it possible to obtain high yields of biologically active proteins by taking into account process parameters such as protein concentration, redox conditions, temperature, pH, and ionic strength.

Antibodies specific for (6-4) DNA photoproducts: cloning, antibody modeling and construction of a single-chain Fv derivative

We have investigated a series of four monoclonal antibodies that specifically recognize pyrimidine (6-4) pyrimidone photoproducts. One of these antibodies (64M4), bound all four possible pyrimidine-pyrimidone photoadducts with equal affinities whereas the others (64M2, 64M3 and 64M5) were selective for TC and TT sequences. In addition, 64M5 had the highest binding affinity for photodamaged DNA of the four [T. Mori et al., Photochem. Photobiol. 54 (1991) 225-232]. To help understand the differences between these antibodies, we have cloned and sequenced the variable region genes from all four. Comparing these sequences revealed that all four were highly similar to one another, although there were some differences in potential antigen-contact regions. To assess the influences of these sequence differences at the structural level, computer models were constructed for all four antibodies. Most of the sequence differences occurred in potential antigen contact regions, suggesting specific positions that might account for the observed differences in binding affinities and selectivities. A single-chain Fv derivative of 64M5 was therefore constructed and characterized to provide an experimental system in which structure-function relationships can be tested. This derivative could be isolated from Escherichia coli using two chromatographic steps and possessed the same binding specificity as the parent monoclonal antibody.

Pharmacological activity of the C-terminal and N-terminal domains of secretory leukoprotease inhibitor in vitro

1. In order to characterize the physiological functions of the domain structure of secretory leukoprotease inhibitor (SLPI), the biological capacities of half-length SLPIs, (Ser1-Pro54)SLPI and (Asn55-Ala107)SLPI, were investigated and compared with those of full-length SLPI. 2. The activities of these inhibitors against several serine proteases were determined using synthetic chromogenic substrates. The inhibitory capacity of the C-terminal domain, (Asn55-Ala107)SLPI, was as strong as that of full-length SLPI against human neutrophil elastase (NE), cathepsin G and chymotrypsin. It possessed less trypsin inhibitory activity than intact SLPI. For the N-terminal domain of SLPI, (Ser1-Pro54)SLPI, no inhibitory activity could be detected against the serine proteases tested in this study. 3. The inhibitory activity of (Asn55-Ala107)SLPI against the proteolysis of the natural substrates elastin and collagen by NE was comparable with that of full-SLPI (elastin, IC50 = 907 +/- 31 nM for SLPI, 767 +/- 33 nM for (Asn55-Ala107)SLPI; collagen, IC50 = 862 +/- 36 nM for SLPI, 727 +/- 47 nM for (Asn55-Ala107)SLPI). 4. The binding affinities of full- and half-length SLPIs for heparin were measured by affinity column chromatography. Full-length SLPI showed high affinity for heparin while the binding capacities of both half-length SLPIs were lower. (Concentration of NaCl for elution, 0.45 M for SLPI, 0.24 M for (Ser1-Pro54)SLPI, 0.27 M for (Asn55-Ala107)SLPI). 5. The effects of full-SLPI and (Asn55-Ala107)SLPI on blood coagulation were measured using the activated partial thromboplastin time (APTT). Full-length SLPI prolonged clotting time dose dependently(1.25, 2.5 and 5.0 microM), whereas (Asn55-AlalO7)SLPI had no effect even at the highest concentration.6. In conclusion, the C-terminal domain of SLPI is a promising candidate for the treatment of inflammatory diseases in which participation of neutrophil proteases has been suggested.

Probing the structure of human growth hormone by limited proteolysis

Digestion of human growth hormone (hGH) with the Glu-specific protease from Staphylococcus aureus V8 was performed at 20-22 degrees C or 37 degrees C at a 1:20 ratio (by weight) at pH 7.8 with or without 0.2% SDS. There are 14 Glu-residues evenly distributed along the polypeptide chain of hGH as possible sites of proteolytic cleavage of V8-protease. The pattern of fragmentation of hGH was analyzed by electrophoresis and reversed-phase HPLC, and the identity of the proteolytic fragments isolated to homogeneity was established by their partial sequencing and amino acid analysis after acid hydrolysis. Kinetic analysis of the proteolytic digestion process allowed to establish that initial nicking of the protein occurs at Glu33 and subsequently at Glu56 and Glu66. Much slower cleavages occur at Glu30 and Glu186. These cleavage sites are located at chain loops in the hGH molecule, and in particular outside the helical segments of the four-helix bundle of the crystal structure of hGH. Fragments 1-33 and 67-191 comprising entirely the N-terminal helix and the three C-terminal helices of hGH, respectively, were isolated to homogeneity in amounts useful for subsequent conformational and functional studies. The results of this study and of previous ones [Li, C.H. (1982) Mol. Cell. Biochem. 46, 31-41] describing limited proteolysis of hGH by various proteases have been interpreted on the basis of the three-dimensional structure and dynamics of hGH. Overall, it is shown that proteolytic enzymes preferentially cleave hGH at exposed and flexible loops only, thus emphasizing the fact that proteases can be used as reliable probes of protein structure and dynamics.

Characteristics of a de novo designed protein

A series of 204 amino acid proteins intended to form TIM (triose phosphate isomerase) barrel structures were designed de novo. Each protein was synthesized by expression of the synthetic gene as a fusion protein with a portion of human growth hormone in an Escherichia coli host. After BrCN treatment, the protein was purified to homogeneity. The refolded proteins are globular and exist as monomers. One of the designed proteins is stable toward guanidine hydrochloride (GuHCl) denaturation, with a midpoint of 2.6 M determined from CD and tryptophan fluorescence measurements. The GuHCl denaturation is well described by a 2-state model. The NMR spectra, the thermal denaturation curves, and the 1-anilino-8-naphthalene sulfonic acid binding imply that the stability of the protein arises mainly from hydrophobic interactions, which are probably of a nonspecific nature. The protein has a similar shape to that of rabbit triosephosphate isomerase, as determined by electron microscopy.

Efficient processing and export of human growth hormone by heat labile enterotoxin chain B signal sequence

The heat-labile enterotoxin chain B (LTB) signal sequence was used for the processing and export of human growth hormone (hGH). The protein was completely processed and exported across the cell membrane to accumulate in the periplasmic space in Escherichia coli. The human growth hormone cDNA was cloned as a PCR amplified fragment under the control of tac promoter and translationally fused to the LTB signal sequence. The rate of processing of hGH under the control of the LTB signal sequence was equal to or more than the rate of induction of expression, indicating efficient processing. The receptor binding activity of the processed periplasmic protein was established in a radio receptor assay.

Inhibition of oxygen toxicity by targeting superoxide dismutase to endothelial cell surface

Since enzymes that degrade reactive oxygens, such as superoxide dismutase (SOD), are significantly lower in plasma than in intracellular compartments, cell surface membranes should be protected against hazardous oxygens particularly when animals are challenged with oxidative stress. To minimize oxygen toxicity on endothelial cell surface, a fusion gene consisting of cDNA coding human Cu2+/Zn2(+)-SOD and heparin-binding peptide was constructed and expressed in yeast. The resulting enzyme (HB-SOD) bound to a heparin-Sepharose column and cultured endothelial cells; binding was inhibited either by high NaCl concentrations or heparin. When injected intravenously, HB-SOD predominantly bound to vascular endothelial cell surface. Carrageenin-induced paw edema and cold-induced brain edema of the rat were markedly inhibited by a single dose of HB-SOD. These results suggest that superoxide radical and/or its metabolite(s) occurring at or near the outer surface of vascular endothelial cells might play a critical role in the pathogenesis of vasogenic edema.

Secretion of recombinant ribonuclease T1 into the periplasmic space of Escherichia coli with the aid of the signal peptide of alkaline phosphatase

The ribonuclease T1 (RNase T1) gene was ligated to a synthetic gene for the signal peptide of Escherichia coli alkaline phosphatase. When this fusion gene was expressed in E. coli under the control of the trp promoter, active RNase T1 having the correct N-terminal sequence was secreted into the periplasmic space, indicating that the heterologous signal peptide had been cleaved off correctly. The enzyme could be readily purified from the periplasmic fraction with a yield of 1.8 mg from 1 liter culture. Adopting the same strategy, it was possible to produce a labile mutant of RNase T1 (Glu-58----Ala mutant) in E. coli, the yield of the purified mutant enzyme being 2.0 mg from 1 liter culture.

27 amino acid residues can be deleted from the N-terminus of human lymphotoxin without impairment of its cytotoxic activity

In order to study the relationship between activity and structure of human lymphotoxin (hLT, 171 aa), we synthesized the gene (519 bp) for hLT and expressed it in Escherichia coli. Purification of the recombinant hLT from crude extracts was difficult because of the low level of expression of the gene. To improve the yield of the recombinant protein, we prepared five truncated genes for mutant proteins in which 25, 26, 27, 28 and 37 amino acid residues, respectively, were missing from the N-terminus. All of the genes were efficiently expressed and adequate amounts of mutant proteins were synthesized. The proteins were recovered mainly in the supernatant fractions after disruption of cells, with the exception of LT delta 37N, in which 37 residues were absent from the N-terminal region. Cytotoxic activities against mouse fibroblast L929 cells were detected in supernatant fractions that contained these mutant proteins, except in the case of LT delta 28N, which lacks the first amino acid residue conserved in both hLT and human tumour necrosis factor (hTNF). LT delta 27N, which is the smallest of the active proteins, was purified to homogeneity, and its cytotoxic activity was found to be similar to that of recombinant hTNF.

Synthesis of a gene for the protein kinase domain of the epidermal growth factor receptor and its expression in Escherichia coli

A gene encoding the protein kinase domain of the epidermal growth factor receptor has been chemically synthesised, cloned and expressed in Escherichia coli. The 942-base-pair gene was constructed by enzymatic ligation of 56 oligonucleotides and cloned into an expression vector downstream of the E. coli trp promoter. Production of active gene product was confirmed by means of a protein kinase assay, demonstrating that the enzymatic activity of the protein kinase domain of the epidermal growth factor receptor is retained after expression in E. coli.

Use of Bacillus brevis for efficient synthesis and secretion of human epidermal growth factor

Using previously isolated Bacillus brevis strains that secrete large amounts of proteins but little protease into the medium, we have developed a host-vector system for very efficient synthesis and secretion of heterologous proteins. The multiple promoters and the signal-peptide-coding region of the MWP gene, a structural gene for one of the major cell wall proteins of B. brevis strain 47, were used to construct expression-secretion vectors. With this system, a synthetic gene for human epidermal growth factor (hEGF) was expressed efficiently and a large amount (0.24 g per liter of culture) of mature hEGF was secreted into the medium. hEGF purified from the culture supernatant had the same NH2-terminal amino acid sequence, COOH-terminal amino acid, and amino acid composition as natural hEGF, and it was fully active in biological assays. These results, in combination with previous results, showed that mammalian proteins can be produced in active form 10-100 times more efficiently in B. brevis than has been reported in other systems.

A comprehensive list of chemically synthesized genes

A databank for chemically synthesized genes has been compiled.

Increase in nucleolytic activity of ribonuclease T1 by substitution of tryptophan 45 for tyrosine 45

The preparation and analysis of a mutant ribonuclease (RNase) T1 which possesses higher nucleolytic activity than the wild-type enzyme are described. The gene for the mutant RNase T1 (Tyr45----Trp45), in which a single amino acid at the binding site of the guanine base has been changed, was constructed by the cassette mutangenesis method using a chemically synthesized gene [Ikehara, M. et al. (1986) Proc. Natl Acad. Sci. USA 83, 4695-4699]. In order to reduce the nucleolytic activity of the enzyme in vivo, this gene was expressed in Escherichia coli as a fused protein connected through methionine residues to other proteins at both the N- and C-termini. After liberation from the fused protein by cleavage with cyanogen bromide at the methionine junctions, the mutant RNase T1 was purified by column chromatography. The nucleolytic activity toward pGpC increased to 120% of that of wild-type RNase T1. The kinetic parameters of the mutant enzyme demonstrate that this higher nucleolytic activity is due to a higher affinity for the substrate, probably because of an increased stacking effect in the binding pocket for the guanine base. This mutant enzyme also possessed a higher nucleolytic activity against pApC than wild-type RNase T1.

The design of synthetic genes

Computer programs are described that aid in the design of synthetic genes coding for proteins that are targets of a research program in site directed mutagenesis. These programs "reverse-translate" protein sequences into general nucleic acid sequences (those where codons have not yet been selected), map restriction sites into general DNA sequences, identify points in the synthetic gene where unique restriction sites can be introduced, and assist in the design of genes coding for hybrids and evolutionary intermediates between homologous proteins. Application of these programs therefore facilitates the use of modular mutagenesis to create variants of proteins, and the implementation of evolutionary guidance as a strategy for selecting mutants.

Cloning and expression in Escherichia coli of a synthetic DNA for hirudin, the blood coagulation inhibitor in the leech

A 235-bp DNA coding for the leech blood coagulation inhibitor, hirudin, was chemically synthesized. The synthesis involved preparation of seven long oligodeoxyribonucleotide pairs which were assembled and cloned using a rapid and simple procedure. More than half of the transformed Escherichia coli cells expressed a biosynthetic polypeptide having biological properties which were very similar to authentic hirudin from the leech Hirudo medicinalis. To achieve efficient expression, we fused the hirudin DNA to a truncated C1 repressor gene of bacteriophage lambda to create a hybrid protein. An additional methionine at the fusion point allowed the active hirudin to be cleaved off by cyanogen bromide.

Expression, secretion and processing of hirudin in E. coli using the alkaline phosphatase signal sequence

A DNA fragment coding for the E. coli phoA signal peptide was synthesized and inserted into the expression vector pKK223-3. A single HindIII restriction site is located just at the end of the signal sequence. A gene coding for the proteinase inhibitor hirudin, which has previously been synthesized, was inserted into this HindIII site. The hybrid protein was expressed under control of the tac-promoter and secreted into the periplasm of E. coli. From the periplasmic fraction two processed proteins were isolated. One of these was identical with desulfatohirudin and also had similar biological properties.

Inquiries into the structure-function relationship of ribonuclease T1 using chemically synthesized coding sequences

The genes for ribonuclease T1 and its site-specific mutants were chemically synthesized and introduced to Escherichia coli. All enzymes were fusion products produced by joining the synthetic gene at specific restriction sites to the synthetic gene for human growth hormone in a plasmid containing the E. coli trp promoter. The fusion protein from this plasmid contained 66% of the amino-terminal sequences of the human growth hormone, which were recognizable immunologically. RNase T1 or its mutants were cleaved from the fusion protein with cyanogen bromide. The synthetic RNase T1 endowed with the revised wild-type triad Gly-Ser-Pro, residues 71-73, was fully functional, readily hydrolyzing pGpC bonds, whereas a mutant enzyme having the originally reported, erroneous triad Pro-Gly-Ser was totally inactive. Various amino acid substitutions were also introduced to the guanosine recognition region comprised of residues 42-45, Tyr-Asn-Asn-Tyr. Substitution of either of the tyrosine residues noted above with phenylalanine had no dramatic effect on the enzyme's function. Replacement of asparagine-43 with arginine or alanine also caused only a small change in the hydrolyzing activity--a mutant enzyme maintained greater than 50% of the wild-type activity. In sharp contrast, when aspartic acid or alanine was substituted for asparagine-44, the activity was dramatically reduced to a few percent of the wild-type activity.