PROCESS FOR PREPARING OLIGOPEPTIDE

Abstract: An oligopeptide is prepared by use of a vector wherein DNA coding for the intended oligopeptide has been intro­ duced into a plasmid including a leader gene and an alpha-amylase structural gene.

Description: Field of Industrial Application: This invention relates to a process for preparing an oligopeptide with genetic engineering techniques. More particularly it relates to a process for preparing an oligopeptide wherein the oligopeptide formed in cells is secreted out of the cells. Description of the Prior Art and Problems thereof: Conventional processes for preparing oligopeptide include a synthetic method and a biochemical method utilizing genetic engineering techniques. The former method usually comprises introducing protective groups into amino or carboxyl groups of amino acids as a starting material before reaction, so that it is necessary to remove said protective groups in the final step. However it becomes more difficult to remove all of these protective groups with an increase in the length of the peptide chain. Thus the obtained product is in the form of a mixture of the aimed oligopeptide and other oligopeptides wherein some of the above protective groups remain. Therefore, it is difficult to purify the aimed oligopeptide. Furthermore, this synthetic method generally gives a poor yield. Major examples of the latter method are those employing Escherichia coli . However, none of them allows the formed oligopeptide to be secreted out of cells. Therefore, it is necessary to break the cells to collect the oligopeptide. The oligopeptide thus collected is generally in the form of a mixture with various peptides, so that it is also difficult and troublesome to purify it. Chemical Abstracts, Volume 97, no. 21, November 22, (1982), Abstract 176164y, discloses a method for cloning and expression of a Bacillus coagulans amylase gene in E. coli . However, this reference does not disclose the use of Bacillus subtilis . EP-036 259 discloses a method for the cloning, expression and secretion of heterologous genes by the insertion of the respective DNA into the Bgl II site of the B. licheniformis beta-lactamase gene and thereby creating fused protein parts containing the leader sequence and the first 71 amino acid residues of the beta-lactamase exoenzyme, when the exact reading frame of the DNA sequence to be inserted is known. However, the reference does not refer to the secretion of a fused protein, in particular not to the secretion of a protein comprising ∝-amylase and an oligopeptide. Means for Solving the Problems: As a result of our studies to overcome these problems of the prior art, we have completed the present invention. Accordingly the present invention provides a process for preparing an oligopeptide comprising the following steps of: (a) inserting DNA coding for the oligopeptide into pTUB 4, which has a leader gene and an ∝-amylase structural gene sequence obtained from Bacillus subtilis NA 64 (FERM BP-423), at site 1 shown in the figure being the Ava II site present at the 1531 st base sequence from the upperstream side of the ∝-amylase structural gene; (b) introducing the pTUB 4 into a Bacillus subtilis cell and obtaining a transformed Bacillus subtilis cell; (c) culturing said transformed Bacillus subtilis cell; (d) secreting a fused protein comprising the ∝-amylase and the oligopeptide out of the transformed Bacillus subtilis cell; and (e) separating the oligopeptide from the fused protein. The DNA coding for the oligopeptide as used in the present invention may be derived from vital tissue cells. Alternately, it may be prepared in a known manner, e.g., through synthesis by a solid phase triester method. The oligopeptide to be produced in the invention preferably includes a hormone such as calcintonin, angiotensin I, bradykinin, somatostatin, insulin and luteotropic hormone, a precursor for each hormone mentioned before, and an antifungal peptide such as gramicidin A and mycobacillin. The plasmid pTUB 4 used in the present invention is prepared by cleaving plasmid pUB 110, derived from Staphylococcus , with a restriction enzyme to thereby open the ring and connecting the ∝-amylase gene sequence obtained from Bacillus subtilis NA 64 (deposited with Fermentation Research Institute, FERM BP-423) to the ring-opened portion in a conventional manner. The ∝-amylase gene refers to the above-mentioned ∝-amylase structural gene from Bacillus subtills NA 64, which codes for ∝-amylase protein, and a lender gene, which codes for a signal peptide for secreting the ∝-amylase out of cells. Our studies have revealed that the ∝-amylase activity of an ∝-amylase protein would be maintained when amino acid bonds of at least 436 molecules starting with the N terminal are sustained. Accordingly a protein of a composition size capable of maintaining its ∝-amylase activity to which an oligopeptide is bonded, which is referred to as a fused protein, might exhibit an amylase activity. Based on the above findings, we have attempted to develop a fused protein having an ∝-amylase activity by introducing DNA coding for the aimed oligopeptide into the ∝-amylase gene of Bacillus subtilis NA 64. The leader gene portion of the ∝-amylase gene may be obtained, e.g., by the process disclosed in our preceding Japanese Patent Application No. 043826/1984. The plasmid pTUB 4 carries genetic information for kanamycin resistance originating from the pUB 110 and that for ∝-amylase, so that strains cloned with this plasmid may be readily selected. Now the process for introducing the DNA coding for the aimed oligopeptide into the palsmid pTUB 4 will be described. Plasmid pTUB 4 may be cleaved with a restriction enzyme Ava II at seven sites. It has been revealed that five sites among them are present in the ∝-amylase structural gene while the residual two are present downstream of the ∝-amylase structural gene. Thus a fused protein having an ∝-amylase activity may be obtained by cleaving the plasmid pTUB 4 at an Ava II incision site present downstream. Various DNA fragments may be obtained by partial digestion of the pTUB 4 with the restriction enzyme Ava II. Among these fragments, a plasmid ring-opened at the Ava II incision site present at the 1531st base sequence from the upperstream side of the ∝-amylase structural gene is selected and DNA coding for the aimed oligopeptide is bonded thereto. Cloning of Bacillus subtilis NA 64 strain with the vector thus obtained makes it possible to secrete the fused protein comprising the ∝-amylase and the oligopeptide out of the cells. As the fused protein is secreted out of the cells by the signal peptide of ∝-amylase, it can be very readily isolated. After removing the cells, the fused protein may be purified in a conventional manner for the purification of ∝-amylase. The fused protein thus obtained is treated in an appropriate manner to give fragments of oligopeptides. The aimed oligopeptide may be readily purified by taking advantage of the properties thereof. Preferred Embodiment of the Invention: To further illustrate the present invention, the following Example will be given. Example Plasmid pUB 110 was treated with a restriction enzyme Bam HI and an ∝-amylase gene derived from B . subtilis NA 64 strain was inserted into the ring-opened plasmid thus obtained to give plasmid pTUB 4. The pTUB 4 was subjected to partial digestion with a restriction enzyme Ava II and subsequently a plasmid ring-opened at site (1) being present at the 1531st base sequence from the upperstream side of the ∝-amylase structural gene, as shown in the following figure, was taken out by electrophoresis. (sites of pTUB 4 which may be cleaved with Ava II) The base sequence in the neighborhood of the cleavage site (1) is as follows: After cleavage with Ava II, Hind III linker was bonded to the cleavage site to give the following DNA sequence: On the other hand, DNA coding for angiotensin I known as a human hormone was synthesized by a solid phase triester method. The DNA thus synthesized corresponded to the following amino acid sequence: Met-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu Methionine was incorporated to readily take out the angiotensin I by a CNBr treatment as described herein below. A termination codon was bonded to the downstream side of the base sequence coding for leucine in the synthetic DNA. Hind III sites were further bonded to the down- and upperstream sides of the synthetic DNA. The synthetic DNA thus obtained was treated with the Hind III as described above wherein Hind III linker was bonded to pTUB 4, thus adding the former to the ring-opend site of the latter to give the following base sequence: The obtained vector wherein the DNA coding for angiotensin I was bonded to pTUB 4 was introduced into the B . subtilis NA 64 strain, thus selecting colonies exhibiting kanamycin resistance. Subsequently colonies certainly including the angiotensin gene were selected by colony hybridization. The strains thus obtained were cultured to produce a fused protein of ∝-amylase and angiotensin I. Similar to the ∝-amylase secreted out of cells by the signal peptide as described above, the formed fused protein was secreted out of the cells. After removing the cells, ammonium sulfate was added to the medium to thereby sediment the protein, which was then dialyzed and passed through a DEAE-cellulose column twice. Thus the fused protein was obtained at a yield of 90 % or above. The fused protein can be cleaved at methionin portions by treating with CNBr. The fused protein may be divided into several peptides by treating with CNBr and a peptide comprising 17 amino acids as the minimum unit may be obtained from the protein originating from ∝-amylase. Angiotensin I is a peptide comprising 10 amino acids as mentioned above. Thus angiotensin I could be purified by treating the mixture of peptides obtained by the CNBr treatment with the DEAE-cellulose column. The angiotensin I thus obtained exhibited its inherent bioactivity. As a result of the analysis of the plasmid of strains producing the fused protein, the abovementioned DNA sequence was confirmed. The symbols used in the above Example stand for the following compounds:

Claims: A process for preparing an oligopeptide comprising the steps of: (a) inserting DNA coding for the oligopeptide into pTUB 4, which has a leader gene and an ∝-amylase structural gene sequence obtained from Bacillus subtilis NA 64 (FERM BP-423), at site 1 shown in the figure being the Ava II site present at the 1531 st base sequence from the upperstream side of the ∝-amylase structural gene; (b) introducing the pTUB 4 into a Bacillus subtilis cell and obtaining a transformed Bacillus subtilis cell; (c) culturing said transformed Bacillus subtilis cell; (d) secreting a fused protein comprising the ∝-amylase and the oligopeptide out of the transformed Bacillus subtilis cell; and (e) separating the oligopeptide from the fused protein.

Inventors: FURUSATO, TAKASHI, OHMURA, KAZUTAKA, SHIROZA, TERUAKI, YAMANE, KUNIO, YAMAZAKI, HISATO
Applicants: DAICEL CHEMICAL INDUSTRIES, LTD., NISSAN CHEMICAL INDUSTRIES LTD., OJI CORN STARCH CO., LTD., THE CALPIS FOOD INDUSTRY CO., LTD., YAMANE, KUNIO
Application year: 1985
Main classification: C12N15
IPC codes: C12P21, C12N9, C12N15, C07K7, C12N1, C12R1