Alteration of amino-terminal codons of human granulocyte-colony-stimulating factor increases expression levels and allows efficient processing by methionine aminopeptidase in Escherichia coli

Insulin related compounds and identification

Insulin-related compounds (IRCs), which originate during the expression and purification of human insulin using recombinant Escherichia coli, were purified and identified. We investigated the identity of IRCs and their origin. We also presented methods for inhibiting IRC formation. The strains used in this report were E. coli B5K and E. coli H27R. E. coli B5K had a 6-amino acid-fused peptide at the N-terminus of proinsulin, and E. coli H27R had a 28-amino acid-fused peptide at the N-terminus of proinsulin. We investigated the identity of IRCs and their origin by mainly using High Performance Liquid Chromatography (HPLC). The well-known IRCs, desamido human insulin and desthreonine human insulin, formed in both strains. In addition to these two IRCs, the B5K strain produced three different IRCs, Arg(A(0))-insulin (IRC 1), prepeptide-insulin (IRC 2), and Glu(A(22))-insulin (IRC 3). The amounts of IRC 1, IRC 2, IRC 3 were approximately 0.1-0.3% after final purification step. Among these IRCs, Arg(A(0))-insulin, prepeptide-insulin, and desthreonine insulin originated from incomplete enzyme reaction. Glu(A(22))-insulin was formed when we used a double stop codon during the expression of preproinsulin; that is, it was formed by the misreading of the first stop codon through the amber mutation. The major IRCs of the H27R strain were human insulin fragment (B1-B21) (IRC 4), and A9(Ser→Asn) amino acid single mutation human insulin (IRC 5), Arg(B(31))-insulin (IRC 6). Human insulin fragment (B1-B21) was formed by β-mercaptoethanol, which was added during refolding. It formed when the disulfide bonds between A-chain and B-chain of human insulin were cut by β-mercaptoethanol, followed by cleavage of the B-chain by trypsin and carboxypeptidase B. A9(Ser→Asn) amino acid single mutation human insulin originated from the mistranslation of A9 serine, such that asparagine was translated instead of serine. Arg(B(31))-insulin originated from incomplete enzyme reaction. The amount of IRC 4 was 10-15% after enzyme reaction. The amounts of IRC 5, IRC 6 were around 0.2% after final purification step. We present methods for inhibiting the formation of IRCs by controlling the amount of enzyme, controlling the rate of enzyme reaction, using a single stop codon, using hydrogen peroxide (H(2)O(2)) to inhibit β-mercaptoethanol, and modifying the A9 codon.

Expression of recombinant human mutant granulocyte colony stimulating factor (Nartograstim) in Escherichia coli

The human granulocyte colony stimulating factor (hG-CSF) plays an important role in hematopoietic cell proliferation/differentiation and has been widely used as a therapeutic agent for treating neutropenias. Nartograstim is a commercial G-CSF that presents amino acid changes in specific positions when compared to the wild-type form, which potentially increase its activity and stability. The aim of this work was to develop an expression system in Escherichia coli that leads to the production of large amounts of a recombinant hG-CSF (rhG-CSF) biosimilar to Nartograstim. The nucleotide sequence of hg-csf was codon-optimized for expression in E. coli. As a result, high yields of the recombinant protein were obtained with adequate purity, structural integrity and biological activity. This protein has also been successfully used for the production of specific polyclonal antibodies in mice, which could be used in the control of the expression and purification in an industrial production process of this recombinant protein. These results will allow the planning of large-scale production of this mutant version of hG-CSF (Nartograstim), as a potential new biosimilar in the market.

Chemical synthesis and improved expression of recombinant human granulocyte colony-stimulating factor cDNA

Recently, granulocyte colony-stimulating factor (G-CSF) has been recognized as a useful molecule for the treatment of a wide range of complex ailments, such as cancer, AIDS, H1N1 influenza, cardiac and neurological diseases. The vast therapeutic potential of G-CSF has induced scientists to develop biotechnological approaches for the synthesis of this pharmacologically active agent. We used a synthetic G-CSF cDNA molecule to produce the target protein by a simple cloning protocol. We constructed the synthetic cDNA using a DNA synthesizer with the aim to increase its expression level by specific sequence modifications at the 5' end of the G-CSF-coding region, decreasing the GC content without altering the predicted amino acid sequences. The identity of the resulting protein was confirmed by a highly specific enzyme-linked immunosorbent assay. In conclusion, a synthetic G-CSF cDNA in combination with the recombinant DNA protocol offers a rapid and reliable strategy for synthesizing the target protein. However, commercial utilization of this methodology will require rigorous validation and quality control.

Human G-CSF synthesis using stress-responsive bacterial proteins

We previously reported that under the stress condition caused by the addition of 2-hydroxyethyl disulfide, a thiol-specific oxidant, to growing cultures of Escherichia coli BL21(DE3), a population of stress-responsive proteins [peptidyl-prolyl cis–trans isomerase B (PpiB), bacterioferritin (Bfr), putative HTH-type transcriptional regulator yjdC (YjdC), dihydrofolate reductase (FolA), chemotaxis protein cheZ (CheZ), and glutathione synthetase (GshB)] were significantly upregulated when compared with the nonstress condition. When those stress-responsive proteins were used as fusion partners for the expression of human granulocyte colony-stimulating factor (hG-CSF), the solubility of hG-CSF was dramatically enhanced in E. coli cytoplasm, whereas almost all of the directly expressed hG-CSF were aggregated to inclusion bodies. In addition, the spectra of circular dichroism measured with the purified hG-CSF were identical to that of standard hG-CSF, implying that the synthesized hG-CSF has native conformation. These results indicate that the bacterial stress-responsive proteins could be potent fusion expression partners for aggregation-prone heterologous proteins in E. coli cytoplasm.

Optimization of the AT-content of codons immediately downstream of the initiation codon and evaluation of culture conditions for high-level expression of recombinant human G-CSF in Escherichia coli

Enhanced therapeutic importance of recombinant human granulocyte colony stimulating factor (rhG-CSF) has encouraged us to develop a processing method for its high-level expression in E. coli. In this study, we established a high-yielding clone by incorporation of silent mutations at N-terminal region of human G-CSF gene. We studied and optimized various parameters of culture conditions connected with the expression of rhG-CSF. The maximum expression was obtained in a defined medium supplemented with 1% glucose. The gene in pET-3a vector in E. coli BL21 (DE3) PLysS host strain was induced with 2 mM isopropyl beta-D: -1-thiogalacto pyronoside. The cell growth and productivity was enhanced about 1.6- and 1.5-folds, respectively when inducing the culture at OD(600) value of 6 than 2. The protein expression was significantly increased by addition of rifampicin at concentration of 200 microg/ml. The AT content of 51.8% with suitable codon sequences at N-terminal region and the concentration of rifampicin were identified as the key factors with a significant impact on protein expression. The specific productivity of 104 mg/OD/l (68.7% of total cellular protein) of rhG-CSF was obtained toward the end of the study, which is almost 1.5 times higher yield than reported so far in the literature.

Sequence specificity and efficiency of protein N-terminal methionine elimination in wheat-embryo cell-free system

Recent improvements in wheat-embryo cell-free translation resulted in a highly productive system for protein preparation. To clarify N-terminal processing of the cell-free system in a preparative-scale (> mg protein product per ml), 20 mutant variants of maltose-binding protein (MalE), each having a different penultimate residue in the sequence Met-Xaa-Ile-Glu-, and 20 glutathione S-transferase (GST) variants, having Met-Xaa-Pro-Ile-sequence, were designed and synthesized. The MalE and GST proteins were purified by amylose-resin and glutathione columns, respectively, followed by analysis of their N-terminal sequences. These investigations revealed that sequence specificity and efficiency of the N-terminal Met (N-Met) elimination in the cell-free system are similar to those reported from investigations in cellular systems or in the wheat-embryo cell-free protein expression system in analytical scale (approximately 10 microg protein product per ml). Cleavage of the N-Met is basically determined by the penultimate amino acid in the polypeptide sequence. In the case of MalE, the cleavage was efficient when the penultimate residue was Ala, Cys, Gly, Pro, Ser or Thr. But, in the case of GST with Pro as the antepenultimate residue, the efficiency was significantly reduced when the penultimate residue was Gly or Thr. We also confirmed that substitution of the antepenultimate residue in MalE to Pro drastically reduced the efficiency of N-Met cleavage when the penultimate residue was Ala, Gly, Pro, Ser or Thr, indicating inhibitory effects of antepenultimate residue Pro on N-Met elimination. These results clarified sequence-specific functions of the endogenous N-terminal processing machinery in the scaled-up wheat-embryo cell-free translation system.

The proteomics of N-terminal methionine cleavage

Methionine aminopeptidase (MAP) is a ubiquitous, essential enzyme involved in protein N-terminal methionine excision. According to the generally accepted cleavage rules for MAP, this enzyme cleaves all proteins with small side chains on the residue in the second position (P1'), but many exceptions are known. The substrate specificity of Escherichia coli MAP1 was studied in vitro with a large (>120) coherent array of peptides mimicking the natural substrates and kinetically analyzed in detail. Peptides with Val or Thr at P1' were much less efficiently cleaved than those with Ala, Cys, Gly, Pro, or Ser in this position. Certain residues at P2', P3', and P4' strongly slowed the reaction, and some proteins with Val and Thr at P1' could not undergo Met cleavage. These in vitro data were fully consistent with data for 862 E. coli proteins with known N-terminal sequences in vivo. The specificity sites were found to be identical to those for the other type of MAPs, MAP2s, and a dedicated prediction tool for Met cleavage is now available. Taking into account the rules of MAP cleavage and leader peptide removal, the N termini of all proteins were predicted from the annotated genome and compared with data obtained in vivo. This analysis showed that proteins displaying N-Met cleavage are overrepresented in vivo. We conclude that protein secretion involving leader peptide cleavage is more frequent than generally thought.

Production of nonclassical inclusion bodies from which correctly folded protein can be extracted

Human granulocyte-colony stimulating factor (hG-CSF), an important biopharmaceutical drug used in oncology, is currently produced mainly in Escherichia coli. Expression of human hG-CSF gene in E. coli is very low, and therefore a semisynthetic, codon-optimized hG-CSF gene was designed and subcloned into pET expression plasmids. This led to a yield of over 50% of the total cellular proteins. We designed a new approach to biosynthesis at low temperature, enabling the formation of "nonclassical" inclusion bodies from which correctly folded protein can be readily extracted by nondenaturing solvents, such as mild detergents or low concentrations of polar solvents such as DMSO and nondetergent sulfobetaines. FT-IR analysis confirmed different nature of inclusion bodies with respect to the growth temperature and indicated presence of high amounts of very likely correctly folded reduced hG-CSF in nonclassical inclusion bodies. The yield of correctly folded, functional hG-CSF obtained in this way exceeded 40% of the total hG-CSF produced in the cells and is almost completely extractable under nondenaturing conditions. The absence of the need to include a denaturation/renaturation step in the purification process allows the development of more efficient processes characterized by higher yields and lower costs and involving environment-friendly technologies. The technology presented works successfully at the 50-L scale, producing nonclassical inclusion bodies of the same quality. The approach developed for the production of hG-CSF could be extended to other proteins; thus, a broader potential for industrial exploitation is envisaged.

Rapidly maturing red fluorescent protein variants with strongly enhanced brightness in bacteria

A rapidly maturing variant of the red fluorescent protein DsRed was optimized for bacterial expression by random mutagenesis. The brightest variant contains six mutations, two of which (S4T and a silent mutation in codon 2) explain most of the fluorescence enhancement. The novel variants are expressed at 9-60-fold higher levels in Escherichia coli compared to DsRed.T3, but are not superior fluorophores on a per molecule basis. In contrast to previously available DsRed variants, DsRed.T3_S4T is sufficiently bright to monitor Salmonella gene expression in infected animals using flow cytometry. However, no fluorescence enhancement was observed in Leishmania or HeLa cells, indicating that these novel variants are specifically useful for bacteria.

Secretory production of human granulocyte colony-stimulating factor in Escherichia coli

Human granulocyte colony-stimulating factor (hG-CSF) is a glycoprotein, consisting of 174 amino acids, which plays an important role in hematopoietic cell proliferation, differentiation of hemopoietic precursor cells, and activation of mature neutrophilic granulocytes. In this study, secretory production of hG-CSF in the periplasmic space of Escherichia coli using the Bacillus sp. endoxylanase signal peptide was examined. For the efficient expression of hG-CSF gene, the first five codons at the N-terminal were altered based on the E. coli high-frequency codon database. The hG-CSF gene fused to the endoxylanase signal sequence was expressed using an inducible trc promoter. However, recombinant E. coli cells were completely lysed after induction with 1 mM isopropyl-beta-D-thiogalactopyranoside. Insertion of a small oligopeptide (13 amino acids) containing the histidine hexamer and factor Xa cleavage site between the signal peptide and the mature hG-CSF protein allowed successful secretion of hG-CSF into the periplasm without cell lysis. Among the several E. coli strains examined, E. coli BL21(DE3) and E. coli MC4100 allowed production of hG-CSF to the highest levels (20-22% of total proteins) with the secretion efficiencies greater than 98%. The circular dichroism spectra showed that the conformation of purified hG-CSF is almost identical to native hG-CSF.

Production of recombinant proteins in Escherichia coli

E. coli is the expression system of choice and a substantial body of literature has accumulated on the successful expression of foreign genes in this host. Several problems with protein expression in E. coli have been encountered, and many have been ultimately solved. This unit describes methods that have been developed for production of recombinant proteins in E. coli and potential pitfalls that may be encountered.

MAPs and POEP of the roads from prokaryotic to eukaryotic kingdoms

Methionine aminopeptidases (MAPs) play important roles in protein processing. MAPs from various organisms, for example E. coli, S. typhimurium, P. furiosus, Saccharomyces cerevisiae, and porcine have been purified to homogeneity and their MAP activities have been tested in vitro and in vivo. The DNA sequence analyses of MAP genes from the above organisms reveal sequence homologies with other prokaryotic MAPs as well as with various eukaryotic homologues of rat p67. The cellular glycoprotein, p67 protects the alpha-subunit of eukaryotic initiation factor 2 (eIF2) from phosphorylation by its kinases. We call this POEP (protection of eIF2alpha phosphorylation) activity of p67. The POEP activity of p67 is observed in different stress-related situations such as during heme-deficiency of reticulocytes, serum starvation and heat-shock of mammalian cells, vaccinia virus infection of mammalian cells, baculovirus infection of insect cells, mitosis, apoptosis, and possibly during normal cell growth. The POEP activity of p67 is regulated by an enzyme, called p67-deglycosylase (p67-DG). When active, p67-DG inactivates p67 by removing its carbohydrate moieties. Remarkable amino acid sequence similarities at the C-terminus of rat p67 with its eukaryotic and prokaryotic homologues which have MAP activities, raise several important questions: i) does rat p67 have MAP activity?; and ii) if it does have MAP activity, how the two activities (POEP and MAP) of p67 are used by mammalian cells during their growth and differentiation. In this review, discussions have been made to evaluate both POEP and MAP activities of p67 and their possible involvement during normal growth and cancerous growth of mammalian cells.

The action of N-terminal acetyltransferases on yeast ribosomal proteins

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to determine the state of N-terminal acetylation of 68 ribosomal proteins from a normal strain of Saccharomyces cerevisiae and from the ard1-Delta, nat3-Delta, and mak3-Delta mutants (), each lacking a catalytic subunit of three different N-terminal acetyltransferases. A total 30 of the of 68 ribosomal proteins were N-terminal-acetylated, and 24 of these (80%) were NatA substrates, unacetylated in solely the ard1-Delta mutant and having mainly Ac-Ser- termini and a few with Ac-Ala- or Ac-Thr- termini. Only 4 (13%) were NatB substrates, unacetylated in solely the nat3-Delta mutant, and having Ac-Met-Asp- or Ac-Met-Glu- termini. No NatC substrates were uncovered, e.g. unacetylated in solely mak3-Delta mutants, consistent with finding that none of the ribosomal proteins had Ac-Met-Ile-, Ac-Met-Leu-, or Ac-Met-Phe- termini. Interestingly, two new types of the unusual NatD substrates were uncovered, having either Ac-Ser-Asp-Phe- or Ac-Ser-Asp-Ala- termini that were unacetylated in the ard1-Delta mutant, and only partially acetylated in the mak3-Delta mutant and, for one case, also only partially in the nat3-Delta mutant. We suggest that the acetylation of NatD substrates requires not only Ard1p and Nat1p, but also auxiliary factors that are acetylated by the Mak3p and Nat3p N-terminal acetyltransferases.

Characterization of the receptor binding determinants of granulocyte colony stimulating factor

We performed a series of experiments using alanine-scanning mutagenesis to locate side chains within human granulocyte colony-stimulating factor (G-CSF) that are involved in human G-CSF receptor binding. We constructed a panel of 28 alanine mutants that examined all surface exposed residues on helices A and D, as well as all charged residues on the surface of G-CSF. The G-CSF mutants were expressed in a transiently transfected mammalian cell line and quantitated by a sensitive biosensor method. We measured the activity of mutant proteins using an in vitro proliferation assay and an ELISA binding competition assay. These studies show that there is a region of five charged residues on helices A and C employed by G-CSF in binding its receptor, with the most important residue in this binding patch being Glu 19. Both wild-type G-CSF and the E19A mutant were expressed in E. coli. The re-folded proteins were found to have proliferative activities similar to the analogous proteins from mammalian cells: furthermore, biophysical analysis indicated that the E19A mutation does not cause gross structural perturbations in G-CSF. Although G-CSF is likely to signal through receptor homo-dimerization, we found no compelling evidence for a second receptor binding region. We also found no evidence of self-antagonism at high G-CSF concentrations, suggesting that, in contrast to human growth hormone (hGH) and erythropoietin (EPO), G-CSF probably does not signal via a pure 2:1 receptor ligand complex. Thus, G-CSF, while having a similar tertiary structure to hGH and EPO, uses different areas of the four helix bundle for high-affinity interaction with its receptor.

Strategies for achieving high-level expression of genes in Escherichia coli

Progress in our understanding of several biological processes promises to broaden the usefulness of Escherichia coli as a tool for gene expression. There is an expanding choice of tightly regulated prokaryotic promoters suitable for achieving high-level gene expression. New host strains facilitate the formation of disulfide bonds in the reducing environment of the cytoplasm and offer higher protein yields by minimizing proteolytic degradation. Insights into the process of protein translocation across the bacterial membranes may eventually make it possible to achieve robust secretion of specific proteins into the culture medium. Studies involving molecular chaperones have shown that in specific cases, chaperones can be very effective for improved protein folding, solubility, and membrane transport. Negative results derived from such studies are also instructive in formulating different strategies. The remarkable increase in the availability of fusion partners offers a wide range of tools for improved protein folding, solubility, protection from proteases, yield, and secretion into the culture medium, as well as for detection and purification of recombinant proteins. Codon usage is known to present a potential impediment to high-level gene expression in E. coli. Although we still do not understand all the rules governing this phenomenon, it is apparent that "rare" codons, depending on their frequency and context, can have an adverse effect on protein levels. Usually, this problem can be alleviated by modification of the relevant codons or by coexpression of the cognate tRNA genes. Finally, the elucidation of specific determinants of protein degradation, a plethora of protease-deficient host strains, and methods to stabilize proteins afford new strategies to minimize proteolytic susceptibility of recombinant proteins in E. coli.

Cloning and complete sequence of the DNA polymerase-encoding gene (BstpolI) and characterisation of the Klenow-like fragment from Bacillus stearothermophilus

A fragment of the DNA polymerase I-encoding gene (polI) from Bacillus stearothermophilus (Bst) was obtained by PCR. This was used as a probe to obtain a full-length gene from a Bst genomic DNA (gDNA) plasmid library. Comparison of the sequence to B. caldotenax (Bca) showed about 93% homology at the amino acid (aa) level. A Klenow-like (BstpolIk) clone was developed and the recombinant protein displayed DNA polymerase activity similar to the wild-type BstPolI enzyme.

Restructuring the translation initiation region of the human parathyroid hormone gene for improved expression in Escherichia coli

Overexpression of native human parathyroid hormone in Escherichia coli was achieved by a modification of the 5' end of the genomic gene sequence, thereby adapting this part of the translation initiation region to the bacterial host. Some simple rules abstracted from optimization studies of translation initiation of a beta-interferon gene were applied. These included (a) extending complementarity of the mRNA to the anticodon loop of tRNAfMet by use of a codon with a purine nucleotide directly following the ATG, (b) avoidance of stable secondary structure in the mRNA by use of synonymous A/U-rich codons, (c) elimination of a potential second Shine-Dalgarno sequence. The appropriate silent changes led to a 20-fold increase in parathyroid hormone production resulting in 4.3% of total soluble protein. This result proves the validity of our simple approach for optimization of foreign gene expression in E. coli.

Production of bovine insulin-like growth factor 2 (bIGF2) in Escherichia coli

Bovine insulin-like growth factor 2 (bIGF2) was produced in inclusion bodies in the cytoplasm of Escherichia coli and accumulated at high levels: 20-25% of total Coomassie-stained bacterial protein. The level of accumulation of bIGF2 was affected by the choice of codons in the 5' end of the coding sequence and by a rpoH mutation in the host cells. Purified recombinant bIGF2 had the native N terminus and the same mitogenic activity as that of bIGF2 purified from bovine serum.

Modification of GP63 genes from diverse species of Leishmania for expression of recombinant protein at high levels in Escherichia coli

Toward the future development of a defined subunit vaccine against leishmaniasis is, high levels of recombinant GP63 for diverse species of Leishmania were produced in Escherichia coli. Several features of Leishmania GP63 genes were simultaneously modified with the polymerase chain reaction (PCR) using either cloned genes or total genomic DNA from Leishmania as template DNA for the PCR amplification reactions. The PCR products included only the coding region for the predicted mature form of GP63 that occurs on the surface of Leishmania, flanked by the appropriate translation signals and cloning sites for the production of recombinant GP63 as nonfusion protein in E. coli. When the codon usage in the GP63 gene was modified to reduce the guanine and cytosine content for the codons adjacent to the ATG initiation codon, rGP63 represented about 50% of total protein in E. coli. Mouse monoclonal antibodies raised against purified Leishmania major rGP63 had equivalent immunoblotting characteristics for native GP63 and recombinant GP63 with respect to linear determinants on GP63 expressed in diverse species of Leishmania. Human T cell lines and clones were derived from a patient infected with Leishmania braziliensis panamensis using rGP63 purified from an L. major GP63 expression clone as antigen.

Random silent mutagenesis in the initial triplets of the coding region: a technique for adapting human glutathione reductase-encoding cDNA to expression in Escherichia coli

The introduction of random silent mutations into the 5'-coding region of a human cDNA as the basis for successful expression in Escherichia coli is demonstrated in four steps. (1) Plasmid pUB200 containing the pRpL promoters of phage lambda was found not to serve as an expression vector for a unchanged human glutathione reductase (hGR)-encoding cDNA. (2) When this cDNA was expressed in a two-cistron context using high-copy-number plasmids, recombinant protein was detected in low yield (0.03% of the total cell protein). (3) Silent mutations were introduced into the triplets coding for the N-terminal amino acids. When screening E. coli colonies transformed with expression plasmids containing cDNA mutants, we identified adapted clones that produced hGR in up to 70-fold higher yield than the clone containing the unchanged cDNA. Sequence analyses of adapted cDNA species revealed lower G + C contents in the modified regions, suggesting altered mRNA structures. (4) When the adapted cDNA sequences were recloned in the vector which had failed to express unchanged hGR cDNA in step 1, synthesis of recombinant protein was as high as in step 3. This means that the yield of expression for adapted cDNA was at least 1000-fold higher than for unchanged cDNA. In conclusion, random silent mutations introduced into the translation initiation region of cDNA might be a useful technique for designing sequence features which favour gene expression.

Cloning and expression of the gene for the cross-reactive alpha antigen of Mycobacterium kansasii

The gene for the extracellular alpha antigen of Mycobacterium kansasii was cloned by using the alpha-antigen gene fragments of M. bovis BCG as probes. Gene analysis revealed that this gene encodes 325 amino acid residues, including 40 amino acids for the signal peptide, followed by 285 amino acids for the mature protein. A comparison of the nucleotide sequences of the genes isolated from these two mycobacterial species showed that the levels of DNA and amino acid homology were 84.8 and 89.1%, respectively. The hydropathy profiles were also compared, and two highly changed hydrophilic regions were observed, which might account for the antigenic diversity of this antigen or its acquirement of antigenic specificity.

Mature apolipoprotein AI and its precursor proApoAI: influence of the sequence at the 5' end of the gene on the efficiency of expression in Escherichia coli

Apolipoprotein AI (ApoAI) plays a central role in the regulation of lipid metabolism. Initial attempts to express human apoAI cDNA in Escherichia coli did not yield detectable levels of the mature protein. By analyzing the efficiency of expression of apoAI-lacZ gene fusions, we have been able to show that the sequence at the 5' end of the ApoAI-coding region is a critical parameter. Indeed, silent changes in the codons for the first 8 residues of ApoAI, which did not alter the amino acid sequence, affected expression dramatically. Analysis of the corresponding mRNA steady-state levels suggested a role for differential mRNA stability in the control of apoAI expression in this system. Among all the possible alternative sequences, we have identified an optimal sequence which, when reinserted in the original expression plasmid, yields high level production of mature ApoAI. This procedure has been extended to the production of the natural variant ApoAI-Milano and the precursor proApoAI. Availability of these recombinant molecules would allow the investigation of their structural and biological features. In addition, the methodology used to optimize ApoAI expression is of general interest in assuring high expression of heterologous proteins in E. coli.

Recombinant human granulocyte-colony stimulating factor and recombinant human macrophage-colony stimulating factor synergize in vivo to enhance proliferation of granulocyte-macrophage, erythroid, and multipotential progenitor cells in mice

Combinations of low dosages of purified recombinant human (rh) macrophage-colony stimulating factor (M-CSF; also termed CSF-1) and rh granulocyte-colony stimulating factor (G-CSF) were compared alone and in combination for their influence on the cycling rates and numbers of bone marrow and splenic granulocyte-macrophage, erythroid, and multipotential progenitor cells in vivo in mice pretreated with iron-saturated human lactoferrin (LF). LF was used to enhance detection of the stimulating effects of exogenously added CSFs. Concentrations of each CSF that were not active in vivo when given alone were active when given together, with the other CSF. The concentrations of rhM-CSF and rhG-CSF needed to increase progenitor cell cycling in the marrow and spleen were reduced by factors of 40-200 when these CSFs were administered in combination with low dosages of the other CSF. At the concentrations of rhM-CSF and rhG-CSF tested, synergism was not noted on absolute numbers of progenitor cells or total nucleated cell counts per organ or circulating in the blood. These findings may have potential relevance when considered in a clinical setting where the CSFs might be used in combination with other biotherapy and/or chemotherapy.