Secretion of active-form Streptoverticillium mobaraense transglutaminase by Corynebacterium glutamicum: processing of the pro-transglutaminase by a cosecreted subtilisin-Like protease from Streptomyces albogriseolus

The transglutaminase secreted by Streptoverticillium mobaraense is a useful enzyme in the food industry. A fragment of transglutaminase was secreted by Corynebacterium glutamicum when it was coupled on a plasmid to the promoter and signal peptide of a cell surface protein from C. glutamicum. We analyzed the signal peptide and the pro-domain of the transglutaminase gene and found that the signal peptide consists of 31 amino acid residues and the pro-domain consists of 45 residues. When the pro-domain of the transglutaminase was used, the pro-transglutaminase was secreted efficiently by C. glutamicum but had no enzymatic activity. However, when the plasmid carrying the S. mobaraense transglutaminase also encoded SAM-P45, a subtilisin-like serine protease derived from Streptomyces albogriseolus, the peptide bond to the C side of 41-Ser of the pro-transglutaminase was hydrolyzed, and the pro-transglutaminase was converted to an active form. Our findings suggest that C. glutamicum has potential as a host for industrial-scale protein production.     

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.     

Expression and secretion of heterologous proteases by Corynebacterium glutamicum.

Genes encoding the basic protease of Dichelobacter nodosus (bprV) and the subtilisin of Bacillus subtilis (aprE) were cloned and expressed in Corynebacterium glutamicum. In each case, enzymatically active protein was detected in the supernatants of liquid cultures. While the secretion of subtilisin was directed by its own signal peptide, the natural signal peptide of the bprV basic protease did not facilitate secretion. A hybrid aprE-bprV gene in which the promoter and signal peptide coding sequences of subtilisin replaced those of bprV could be expressed, and basic protease was secreted by C. glutamicum. Expression of these proteases in C. glutamicum provides an opportunity to compare protein secretion from this gram-positive host with that from other gram-positive and gram-negative bacteria.     

Overproduction of human epidermal growth factor/urogastrone in Escherichia coli and demonstration of its full biological activities

A man-made gene coding for [21-Leu] human epidermal growth factor (hEGF)/β-urogastrone was constructed, inserted into a lacZ fusion-gene expression vector, and cloned into Escherichia coli. In the cloned cells the β-galactosidase/hEGF fusion gene was efficiently expressed and the yield of the hybrid protein reached 10% of the total cellular protein. The [21-Leu] hEGF synthesized in the bacterial cells was proved to be as functional as the natural hEGF or urogastrone and mouse EGF by the following criteria: (1) stimulation of cell proliferation, (2) stimulation of thymidine incorporation into cultured cells, (3) competition with mouse EGF for binding sites on the plasma membrane of human KB cells, and (4) stimulation of phosphorylation of a membrane-bound protein of human KB cell, which has an apparent molecular weight of 150 000 to 170 000 and is indistinguishable from the protein phosphorylated in the presence of mouse EGF in the sodium dodecyl sulfate—polyacrylamide electrophoretic gel. The hEGF produced in the bacterial cells also resulted in precocious eyelid-opening by the daily subcutaneous injection into newborn mice and in accelerated incisor eruption in the animals as mouse EGF did, indicating that the hEGF is also fully active in vivo or physiologically.     

Cloning and nucleotide sequence of the csp1 gene encoding PS1, one of the two major secreted proteins of Corynebacterium glutamicum: the deduced N-terminal region of PS1 is similar to the Mycobacterium antigen 85 complex

Two proteins, PS1 and PS2, were detected in the culture medium of Corynebacterium glutamicum and are the major proteins secreted by this bacterium. No enzymatic activity was identified for either of the two proteins. Immunologically cross-reacting proteins were found in a variety of C. glutamicum strains but not in the coryneform Arthrobacter aureus. The gene encoding PS1, csp1, was cloned in lambda gt11 using polyclonal antibodies raised against PS1 to screen for producing clones. The csp1 gene was expressed in Escherichia coli, presumably from its own promoter, and directed the synthesis of two proteins recognized by anti-PS1 antibodies. The major protein band, of lower M(r), was detected in the periplasmic fraction. It had the same M(r) as the PS1 protein band detected in the supernatant of C. glutamicum cultures and presumably corresponds to the mature form of PS1. The minor protein band appears to be the precursor form of PS1. The nucleotide sequence of the csp1 gene was determined and contained an open reading frame encoding a polypeptide with a calculated molecular weight of 70,874, with a putative signal peptide with a molecular weight of 4411. This is consistent with the M(r) determined for PS1 from C. glutamicum culture supernatant and E. coli whole-cell extracts. The NH2-half of the deduced amino acid is similar (about 33% identical residues and 52% including similar residues) to the secreted antigen 85 protein complex of Mycobacterium. The csp1 gene in C. glutamicum was disrupted without any apparent effect on growth or viability.     

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.     

Synthesis and secretion of an epidermal growth factor (EGF) by human fibroblast cells in culture

Human fibroblast (WS-1) cells in culture synthesized and secreted an epidermal growth factor which cross-reacted with human epidermal growth factor (hEGF) purified from human urine. hEGF secreted by the cells (designated as WS-1 EGF or fibroblast EGF) and hEGF isolated from urine (designated as urine EGF) were immunologically indistinguishable. The molecular weight of fibroblast EGF estimated by gel filtration was identical with that of hEGF from urine. On chromatofocusing chromatography, fibroblast EGF was eluted mainly at pH 4.26 as a sharp symmetric peak with a minor peak at pH 4.62, like urine EGF. These results suggested that EGF synthesized and secreted by human fibroblast cells is an identical molecule to that of hEGF in human urine.     

Phosphate starvation-inducible gene ushA encodes a 5' nucleotidase required for growth of Corynebacterium glutamicum on media with nucleotides as the phosphorus source

Phosphorus is an essential component of macromolecules, like DNA, and central metabolic intermediates, such as sugar phosphates, and bacteria possess enzymes and control mechanisms that provide an optimal supply of phosphorus from the environment. UDP-sugar hydrolases and 5' nucleotidases may play roles in signal transduction, as they do in mammals, in nucleotide salvage, as demonstrated for UshA of Escherichia coli, or in phosphorus metabolism. The Corynebacterium glutamicum gene ushA was found to encode a secreted enzyme which is active as a 5' nucleotidase and a UDP-sugar hydrolase. This enzyme was synthesized and secreted into the medium when C. glutamicum was starved for inorganic phosphate. UshA was required for growth of C. glutamicum on AMP and UDP-glucose as sole sources of phosphorus. Thus, in contrast to UshA from E. coli, C. glutamicum UshA is an important component of the phosphate starvation response of this species and is necessary to access nucleotides and related compounds as sources of phosphorus.     

High-level expression, purification, and crystallization of recombinant rat leukotriene C(4) synthase from the yeast Pichia pastoris

Chemical-enzymatic synthesis of human Epidermal Growth Factor (hEGF) cDNA has been performed, following by cloning into expression vector pTWIN1 (New England Biolabs). The resulting recombinant fusion protein expressed in Escherichia coli consisted of the N-terminal chitin-binding domain, mini-intein Ssp dnaB domain and hEGF polypeptide at the C-terminus. In this construct, mini-intein Ssp dnaB played a role of catalytically active subunit capable under certain conditions of autocatalytic cleavage resulting in separation of the target protein. As the hybrid protein had several cysteins in its sequence-one in chitin-binding domain, one in mini-intein and six in hEGF, it was necessary to work out optimal scheme for refolding and purification of the recombinant hEGF. As a result of this work, two schemes of the recombinant hEGF purification have been developed: according to the first scheme, the recombinant protein with reduced cysteins is bound to the chitin column, the hEGF is cleaved off and eluted, and then refolded to form appropriate cystein bridges. In the second scheme, the entire hybrid protein is first refolded to form disulfide bonds and then loaded to affinity resin; the recombinant hEGF is cleaved off and eluted in its native state. In spite of the fact that the first scheme is more common and suitable for a variety of recombinant proteins, in case of recombinant hEGF, the second scheme proved to be more productive and cost-effective.     

人表皮生长因子（hEGF）基因在蓝藻中的表达

人表皮生长因子（hEGF)是由53个氨基酸组成的蛋白,在临床上内服与外敷可促进内外表皮细胞的生长。将人工合成的hEGF基因连接到质粒pRL-489上,位于启动子psb下游。验证连接成功后,用三亲接合转移方法将载体pRL-hEGF导入聚球藻Synechococcus sp.PCC7002和鱼腥藻Anabeana sp.PCC7120。由于pRL-hEGF没有能在单细胞蓝藻中自主复制的复制子,通过筛选,hEGF在聚球藻7002中是整合到蓝藻染色体上进行表达的。用PCR扩增的方法在两种转基因藻中均检测到hEGF基因的存在。放射免疫分析证明,hEGF基因在两种转基因藻中均得到了表达。而且,在聚球藻7002中是采用分泌形式将表达产物分泌到培养液中。     

An improved procedure for production of human epidermal growth factor from recombinant E. coli

An improved procedure for the fermentation and purification of human epidermal growth factor (hEGF) was developed. Recombinant Escherichia coli HB-101 [lacUV5omp08hEGF] harboring plasmid lacUV5omp08hEGF encoding hEGF was used in fermentation to increase levels of hEGF. Medium composition, and the levels of inoculum, inducer (isopropyl-beta-D-thiogalactoside) and ampicillin were optimized with respect to volumetric fermentation of hEGF. As a result, the hEGF concentration reached a high value of 242 mg l(-1) and the amount of heterogeneous protein decreased by 62% compared with that before optimization in batch fermentation. High-quality hEGF was purified from the fermentation culture by centrifugation, salting-out, resuspension, recentrifugation and finally gel chromatography on a Grad-iFrac System using Sephadex G-50 superfine. The purity of hEGF and the total yield were more than 94% and higher than 36%, respectively, and SDS-PAGE of the purified hEGF demonstrated a single band corresponding to an hEGF standard. In particular, a very important phenomenon was found, i.e. that the amount of heterogenous protein in fermentation broths cultured in media with high concentrations of lactose is far less than that cultured in media with high concentrations of glucose.     

Heterologous expression of the Mycobacterium tuberculosis gene encoding antigen 85A in Corynebacterium glutamicum.

By using appropriate Corynebacterium glutamicum-Escherichia coli shuttle plasmids, the gene encoding the fibronectin-binding protein 85A (85A) from Mycobacterium tuberculosis was expressed in C. glutamicum, also an actinomycete and nonsporulating gram-positive rod bacterium, which is widely used in industrial amino acid production. The 85A gene was weakly expressed in C. glutamicum under the control of the ptac promoter from E. coli, but it was produced efficiently under the control of the promoter of the cspB gene encoding PS2, one of the two major secreted proteins from C. glutamicum. The 85A protein was produced in various forms, with or without its own signal sequence and with or without the signal sequence and the NH2-terminal (18-amino-acid) mature sequence of PS2. Western blot analysis with monoclonal antibodies raised against the M. tuberculosis antigen 85 complex showed that recombinant 85A protein was present in the corynebacterial cell wall extract and also released in extracellular culture medium. NH2-terminal microsequencing of recombinant 85A secreted by C. glutamicum showed that signal peptide was effectively cleaved off at the predicted site. The recombinant 85A protein was biologically active in vitro, inducing significant secretion of Th1 T-cell cytokines, particularly interleukin-2 and gamma interferon, in spleen cell cultures from mice vaccinated with live Mycobacterium bovis BCG. Heterologous expression of mycobacterial antigens in C. glutamicum now offers a potent tool for further immunological characterization and large scale preparation of these recombinant proteins.     

Cloning and expression of the ccdA-associated thiol-disulfide oxidoreductase (catA) gene from Brevibacillus choshinensis: stimulation of human epidermal growth factor production

Brevibacillus choshinensis (Bacillus brevis) is a protein-hyperproducing bacterium with a useful host-vector system for the production of recombinant proteins. Here, we cloned the ccdA-catA (cmacr;cdA āssociated thioredoxin-like tmacr;hiol-disulfide oxidoreductase) locus of B. choshinensis HPD31-S5. CatA protein (molecular weight, 19664) contains a thioredoxin-like motif, Cys-Gly-Pro-Cys. It was successfully expressed in B. choshinensis extracellularly ( approximately 100 microg x ml(-1) culture) using the secretion vector pNCMO2, and in Escherichia coli intracellularly ( approximately 350 microg x ml(-1) culture) with an amino-terminal His-tag. Both recombinant proteins showed thiol-disulfide oxidoreductase activity. Incubation of non-native human epidermal growth factor (hEGF) containing incorrect disulfide bonds with B. choshinensis cells secreting CatA protein resulted in the stimulation of the conversion of non-native hEGF to the native form. Furthermore, co-expression of CatA protein with recombinant hEGF in the B. choshinensis production system increased the yield of native hEGF.     

Molecular nature of human epidermal growth factor (hEGF)-like immunoreactivity in human plasma

To investigate the molecular features of hEGF in the circulatory system, we analyzed hEGF-like immunoreactivity (hEGF-LI) in human serum and plasma by our two-site enzyme immunoassay (EIA), using an aliquot of each fraction obtained by gel filtration of human serum or plasma on Sephadex G-100. The results demonstrated that the majority of the hEGF-LI in the plasma (HMW X hEGF-LI) emerged in the void volume, while a small amount of hEGF-LI (LMW X hEGF-LI) eluted at a position similar with that of standard hEGF. After reduction of HMW X hEGF-LI with 2-mercaptoethanol, hEGF-LI emerged at the same elution position as that of standard hEGF, suggesting that the predominant form of hEGF may circulate as a complex with some macromolecule(s) in human blood. The biochemical properties of the plasma component(s) with high molecular weight which form the complex with hEGF and the physiological significance of this circulating complex still remain to be clarified.     

Expression of a fusion protein containing human epidermal growth factor and the collagen-binding domain of <Emphasis Type="Italic">Vibrio mimicus</Emphasis> metalloprotease

Human epidermal growth factor (hEGF) is a polypeptide of 53 amino acids, is an important autocrine/paracrine factor in the human body, and is used in the pharmaceutical and cosmetics industries. We constructed a fusion hEGF protein with a collagen-binding domain (CBD) composed of 33 amino acids from Vibrio mimicus metalloprotease (VMCBD). The CBD segment of the metalloprotease was fused at the C terminus of the hEGF protein. The recombinant fusion protein was expressed in Escherichia coli and purified. The purified hEGF protein promoted greater growth of human/A-431 cells than did the control hEGF. The fusion EGF protein also showed collagen-binding activity with type I collagen. In contrast, hEGF did not bind to type I collagen. These results suggest that recombinant hEGF protein fused to VMCBD may be able to remain for a long period at injured epidermal tissue acting as a healing agent.     

Purification and characterization of epidermal growth factor (beta-urogastrone) and epidermal growth factor fragments from large volumes of human urine

We purified human epidermal growth factor (hEGF) and hEGF fragments from a benzoic acid precipitate of the materials not adsorbed to silica gel in 330 liters of human urine by a relatively brief, simple, and efficient method employing sequential batch absorption to and stepwise elution from CM-cellulose and DEAE-cellulose, Bio-Gel P-10 chromatography in 50 mM HCl, and three reverse-phase HPLC steps for final resolution and purification of hEGF components. Recovery of hEGF was 29%. Eight apparently homogeneous hEGF components were recovered, each of which had similar activities in a homologous hEGF radioimmunoassay and an EGF radioreceptor assay using human placental membranes. Amino acid composition analysis indicated that there were four pairs of components that represented intact 53-amino acid hEGF, hEGF-(1-52), hEGF-(1-51), and hEGF-(1-50); intact hEGF accounted for one-third of the total materials recovered. Automated Edman degradation of each component for at least 10 cycles revealed a single amino acid sequence identical to that proposed for human beta-urogastrone. Similar immunoreactive hEGF components were observed in similar proportions in freshly voided urine, indicating that they were not artifacts of the purification process. Thus, multiple forms of fully biologically active hEGF (i.e., beta-urogastrone) can be relatively easily and efficiently purified from large volumes of human urine.     

Functional analysis of the twin-arginine translocation pathway in Corynebacterium glutamicum ATCC 13869

Compared to those of other gram-positive bacteria, the genetic structure of the Corynebacterium glutamicum Tat system is unique in that it contains the tatE gene in addition to tatA, tatB, and tatC. The tatE homologue has been detected only in the genomes of gram-negative enterobacteria. To assess the function of the C. glutamicum Tat pathway, we cloned the tatA, tatB, tatC, and tatE genes from C. glutamicum ATCC 13869 and constructed mutants carrying deletions of each tat gene or of both the tatA and tatE genes. Using green fluorescent protein (GFP) fused with the twin-arginine signal peptide of the Escherichia coli TorA protein, we demonstrated that the minimal functional Tat system required TatA and TatC. TatA and TatE provide overlapping function. Unlike the TatB proteins from gram-negative bacteria, C. glutamicum TatB was dispensable for Tat function, although it was required for maximal efficiency of secretion. The signal peptide sequence of the isomaltodextranase (IMD) of Arthrobacter globiformis contains a twin-arginine motif. We showed that both IMD and GFP fused with the signal peptide of IMD were secreted via the C. glutamicum Tat pathway. These observations indicate that IMD is a bona fide Tat substrate and imply great potential of the C. glutamicum Tat system for industrial production of heterologous folded proteins.     

Characterization of the in vivo acceptors of the mycoloyl residues transferred by the corynebacterial PS1 and the related mycobacterial antigens 85

Mycolic acids, long-chain (C70-C90) alpha-alkyl, beta-hydroxy fatty acids, are characteristic cell envelope components of mycobacteria; similar but shorter-chain substances occur in corynebacteria and related taxa. These compounds apparently play an important role in the physiology of these bacteria. The deduced N-terminal region of PS1, one of the two major secreted proteins of Corynebacterium glutamicum encoded by the csp1 gene, is similar to the antigens 85 complex of Mycobacterium tuberculosis which has been shown to be associated in vitro with a mycoloyltransferase activity onto trehalose. Overexpression of PS1 in the wild-type strain of C. glutamicum suggested the implication of the protein in the transfer of corynomycolates, evidenced by an increase esterification of the cell wall arabinogalactan with corynomycolic acid residues and an accumulation of trehalose dicorynomycolates. Overexpression of truncated forms of PS1 demonstrated that the crucial region for transfer activity of the protein involves all the region of homology with antigens 85. To establish the putative mycoloyltransferase activity of PS1, a csp1-inactivated mutant of C. glutamicum was biochemically characterized. Inactivation of the gene resulted in: (i) a 50% decrease in the cell wall corynomycolate content; (ii) the alteration of the permeability of the C. glutamicum cell envelope; (iii) the decrease of the trehalose dicorynomycolate content; (iv) the accumulation of trehalose monocorynomycolate; and (v) the appearance of a glycolipid identified as 6-corynomycoloylglucose. Complementation of the mutant by the csp1 gene fully restored the wild-type phenotype. Finally, a mycoloyltransferase assay established that PS1 possesses a trehalose mycoloyltransferase activity. To define the in vivo function of antigens 85, the csp1-inactivated mutant was complemented with the fbpA, fbpB or fbpC genes. Complementation with the different fbp genes restored the normal cell wall corynomycolate content and permeability, but did not affect either the fate of trehalose corynomycolates or the occurrence of glucose corynomycolate. Thus, PS1 is one of the enzymes that transfer corynomycoloyl residues onto both the cell wall arabinogalactan and trehalose monocorynomycolate, whereas in the whole bacterium the mycobacterial antigens 85A, 85B and 85C can transfer mycolates only onto the cell wall acceptor in C. glutamicum.     

Distinct primary translation products from human liver mRNA give rise to secreted and cell-associated forms of complement protein C2

The second component of complement (C2), is a class III major histocompatibility complex gene product and a glycoprotein in the classical complement activating system. Synthesis in the human hepatoma-derived cell line HepG2 results in three intracellular forms: an 84-kDa form secreted in 1-2 h; 79-kDa and 70-kDa forms that remain cell-associated for intervals up to 12 h. All three forms are C2 polypeptides as demonstrated by inhibition of immunoprecipitation with unlabeled C2 and the presence of common major peptide fragments following chymotryptic digestion. The cell-associated forms of C2 are not products of proteolysis as demonstrated by experiments with multiple proteinase inhibitors and by observations of the kinetics of synthesis. Inhibition of core glycosylation by tunicamycin and deglycosylation by acid hydrolysis indicate that the three intracellular C2 polypeptides are glycosylated to a similar extent. Although the 84-kDa form of C2 is susceptible to C1s cleavage, the two cell-associated forms are not. Cell-free biosynthesis by mRNA from HepG2 or human liver results in three primary translation products corresponding to the three unglycosylated forms of C2. These results indicate that HepG2 cells synthesize C2 protein in both secreted and cell-associated forms and that each form is derived from a separate primary translation product.     

The Corynebacterium glutamicum gene pmt encoding a glycosyltransferase related to eukaryotic protein-O-mannosyltransferases is essential for glycosylation of the resuscitation promoting factor (Rpf2) and other secreted proteins

Two-dimensional gel electrophoresis and immunoassays revealed several proteins of the secretory subproteome of Corynebacterium glutamicum to be glycosylated. By genome-wide searches for genes involved in glycosylation, the C. glutamicum gene cg1014 was found to exhibit significant similarity to eukaryotic protein-O-mannosyltransferases (PMTs) and to a recently identified orthologue of Mycobacterium tuberculosis, Rv1002c, which is responsible for protein-O-mannosylation. The putative membrane protein Cg1014 showed the same predicted transmembrane topology as Saccharomyces cerevisiae PMT1 and M. tuberculosis Rv1002c along with conserved amino acid residues responsible for catalytic activity. Deletion of the C. glutamicum pmt gene (cg1014) caused a complete loss of glycosylation of secreted proteins including the resuscitation promoting factor 2 (Rpf2), which is involved in intercellular communication and growth stimulation of C. glutamicum. Because the gene pmt as well as rpf genes are present in the genomes of all actinobacteria sequenced so far, this work provides new insights into bacterial protein glycosylation and new opportunities to elucidate the molecular mechanisms of Rpf activity in pathogenic growth and infection.