Chemistry: natural resins or derivatives; peptides or proteins; – Peptides of 3 to 100 amino acid residues – Insulin; related peptides
Reexamination Certificate
1999-05-07
2001-08-28
Schwartzman, Robert A. (Department: 1636)
Chemistry: natural resins or derivatives; peptides or proteins;
Peptides of 3 to 100 amino acid residues
Insulin; related peptides
C435S069100, C435S069400, C435S070100, C435S252300, C435S325000, C435S455000, C530S303000, C530S305000
Reexamination Certificate
active
06281329
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multi-purpose vector. The vector can be for expressing at least one heterologous protein in a suitable cell such as
E. coli
or other Gram negative bacteria. More specifically, the present invention relates to: a vector for expression of heterologous proteins comprising nucleic acid molecules for: an origin of replication region, optionally but preferably a selection marker (which can be a coding nucleic acid molecule inserted in a restriction site), a promoter, an initiation region e.g. a translation initiation region and/or a ribosome binding site, at least one restriction site and preferably multiple restriction sites, and a transcription terminator; a method for extracting recombinant protein without lysing the cell, e.g., bacteria; and a method for purifying isolated recombinant protein. The vector can facilitate the thermo-regulated production of a heterologous protein or proteins, e.g., pro-insulin.
Several publications are referenced in this application. Full citation to these publications is found at the end of the specification, immediately preceding the claims, or where the publication is mentioned; and each of these publications is hereby incorporated by reference. These publications relate to the state of the art to which the invention pertains; however, there is no admission that any of these publications is indeed prior art.
BACKGROUND OF THE INVENTION
Recombinant DNA technology has enabled the expression of foreign (heterologous) proteins in microbial and other host cells. A vector containing genetic material directing the host cell to produce a protein encoded by a portion of the heterologous DNA sequence is introduced into the host, and the transformant host cells can be fermented and subjected to conditions which facilitate the expression of the heterologous DNA, leading to the formation of large quantities of the desired protein.
The advantages of using a recombinantly produced protein in lieu of isolation from a natural source include: the ready availability of raw material; high expression levels, which is especially useful for proteins of low natural abundance; the ease with which a normally intracellular protein can be excreted into the expression medium, facilitating the purification process; and the relative ease with which modified (fusion) proteins can be created to further simplify the purification of the resultant protein.
However, the aforementioned benefits of recombinant DNA technology are also accompanied by several disadvantages, namely: the required elements of the active protein which result from post-translational modification (i.e., glycosylation) may not be carried out in the expression medium; proteolytic degradation of newly formed protein may result upon expression in host cells; and the formation of high molecular weight aggregates, often referred to as “inclusion bodies” or “refractile bodies”, which result from the inability of the expressed proteins to fold correctly in an unnatural cellular environment. The recombinant protein cannot be excreted into the culture media upon formation of inclusion bodies.
Inclusion bodies contain protein in a stable non-native conformation; or, the protein aggregates may be amorphous, comprised of partially and completely denatured proteins, in addition to aberrant proteins synthesized as a result of inaccurate translation. Such inclusion bodies constitute a large portion of the total cell protein.
Inclusion bodies present significant problems during the purification of recombinant proteins, as they are relatively insoluble in aqueous buffers. Denaturants and detergents, i.e., guanidine hydrochloride, urea, sodium dodecylsulfate (SDS) and Triton X-100, may be necessary to isolate the proteins from the inclusion bodies, often at the expense of the biological activity of the protein itself, resulting from incorrect folding and modification of the amino acid residues in the sequence.
Additionally, a result of the expression of recombinant DNA in
E. coli
is the accumulation of high concentrations of acetate in the media, mainly during the induction phase. The deleterious effect of acetate accumulation (greater than 5 g/L) on cell growth and recombinant protein expression has been well documented in the literature.
Further, the recovery of the desired protein from inclusion bodies is often complicated by the need to separate the desired protein from other host cellular materials, in addition to separating the desired protein from inclusion body heterologous protein contaminants. The latter problem results from the strong attraction that inclusion body proteins have for one another, due to strong ionic and hydrophobic interactions.
Consequently, most established protocols for the isolation of recombinant proteins from inclusion bodies result in large quantities of biologically inactive material, and very low yields of active protein, uncontaminated by extraneous heterologous protein.
Researchers have focused on the manipulation of phage in order to stimulate protein synthesis by a variety of methods.
The promoters of the Lambda phage (P
L
and P
R
) are strong promoters that are negatively controlled by the repressor coded by the gene cl. The mutation cl
857
rendered the repressor inactivate at temperatures above 37° C. Thus, the expression of a sequence controlled by these promoters and by the repressor cl
857
can be activated by a simple change in temperature. These promoters are often used in
E. coli
expression vectors, because they are strong and efficiently repressed (Denhardt & Colasanti, 1987).
Remaut et al. (1981) constructed a set of plasmids containing the promoter P
L
. The promoter and the trp region of the gene were taken from a family of phages (trp44) and inserted in the plasmid pBR322, creating the first plasmid of a series, plasmid pPLa2. After several manipulations, other plasmids were obtained. The plasmids pPLa2 and pPLa8 contained the promoter P
L
fragment, the origin of replication, the ampicillin resistance gene from the plasmid pBR322, and a kanamycin resistance gene from the plasmid pMK20. The promoter region contained the promoter/operator and the nutL site (antitermination), but it was lacking the beginning of the gene N.
The plasmids pPLc236, pPLc28 and pPLc24 are different from the previously identified plasmids, with respect to the direction of transcription from the promoter P
L
in relation to the orientation of the origin of replication, as found in pBR322 (a=anticlockwise, c=clockwise). The kanamycin resistance gene is absent in these three vectors. The difference between pPLc236 and pPLc8 is the presence or absence of a region (present in the former and absent in the latter), which affects the region of unique cloning sites. pPLc24 was derived from pPLc28 by insertion of a region containing the ribosome binding site of the gene for replicase from the phage MS2, enabling the expression of eukaryotic genes.
These plasmids were tested with the expression of different genes, e.g., the gene trpA from
Salmonella typhimurium,
cloned in the plasmid pPLc23 (predecessor of pPLc236), which showed 40% induction of product in relation to the total cellular protein. pLc236 programmed in
E. coli
resulted in a expression of the gene ROP as 20% of the total protein (Muesing et al., 1984). The proteins p4 and p3 of the phage 29 of
Bacillus subtilis,
were also produced from pPLci and reached 30% and 6%, respectively, of the total cellular protein induced in
E. coli,
after thermal induction (Mellado & Salas, 1982).
In 1983, Remault et al. (1983a) built a plasmid pPLc245, derived from pPLc24, in which the initial coding region of replicase was deleted and a region with several unique cloning-sites was added, permitting direct expression. The gene for human &agr;-interferon was cloned into this plasmid, resulting in induction of protein of approximately 2% to 4% of the total cellular protein. For &agr;-interferon, the levels of expression varied from 3% to 25% of the cellular protein, depending on the pl
Astolfi Filho Spartaco
de Lima Beatriz Dolabela
Ribeiro Tunes de Sousa Heloisa
Thiemann Josef Ernst
Vilela Luciano
Biobrás S.A.
Frommer & Lawrence & Haug LLP
Haug Edgar H.
Kowalski Thomas J.
Schwartzman Robert A.
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