Molecular cloning and expression of the VP1 gene of foot-and-mouth disease virus C1 in E. coli: effect on bacterial cell viability

Remarkable stability of an instability-prone lentiviral vector plasmid in Escherichia coli Stbl3

Large-scale production of plasmid DNA to prepare therapeutic gene vectors or DNA-based vaccines requires a suitable bacterial host, which can stably maintain the plasmid DNA during industrial cultivation. Plasmid loss during bacterial cell divisions and structural changes in the plasmid DNA can dramatically reduce the yield of the desired recombinant plasmid DNA. While generating an HIV-based gene vector containing a bicistronic expression cassette 5′-Olig2cDNA-IRES-dsRed2-3′, we encountered plasmid DNA instability, which occurred in homologous recombination deficient recA1 Escherichia coli strain Stbl2 specifically during large-scale bacterial cultivation. Unexpectedly, the new recombinant plasmid was structurally changed or completely lost in 0.5 L liquid cultures but not in the preceding 5 mL cultures. Neither the employment of an array of alternative recA1 E. coli plasmid hosts, nor the lowering of the culture incubation temperature prevented the instability. However, after the introduction of this instability-prone plasmid into the recA13E. coli strain Stbl3, the transformed bacteria grew without being overrun by plasmid-free cells, reduction in the plasmid DNA yield or structural changes in plasmid DNA. Thus, E. coli strain Stbl3 conferred structural and maintenance stability to the otherwise instability-prone lentivirus-based recombinant plasmid, suggesting that this strain can be used for the faithful maintenance of similar stability-compromised plasmids in large-scale bacterial cultivations. In contrast to Stbl2, which is derived wholly from the wild type isolate E. coli K12, E. coli Stbl3 is a hybrid strain of mixed E. coli K12 and E. coli B parentage. Therefore, we speculate that genetic determinants for the benevolent properties of E. coli Stbl3 for safe plasmid propagation originate from its E. coli B ancestor.

Development of vaccines toward the global control and eradication of foot-and-mouth disease

Foot-and-mouth disease (FMD) is one of the most economically and socially devastating diseases affecting animal agriculture throughout the world. Although mortality is usually low in adult animals, millions of animals have been killed in efforts to rapidly control and eradicate FMD. The causing virus, FMD virus (FMDV), is a highly variable RNA virus occurring in seven serotypes (A, O, C, Asia 1, Sat 1, Sat 2 and Sat 3) and a large number of subtypes. FMDV is one of the most infectious agents known, affecting cloven-hoofed animals with significant variations in infectivity and virus transmission. Although inactivated FMD vaccines have been available for decades, there is little or no cross-protection across serotypes and subtypes, requiring vaccines that are matched to circulating field strains. Current inactivated vaccines require growth of virulent virus, posing a threat of escape from manufacturing sites, have limited shelf life and require re-vaccination every 4-12 months. These vaccines have aided in the eradication of FMD from Europe and the control of clinical disease in many parts of the world, albeit at a very high cost. However, FMDV persists in endemic regions impacting millions of people dependent on livestock for food and their livelihood. Usually associated with developing countries that lack the resources to control it, FMD is a global problem and the World Organization for Animal Health and the United Nations' Food Agriculture Organization have called for its global control and eradication. One of the main limitations to FMDV eradication is the lack of vaccines designed for this purpose, vaccines that not only protect against clinical signs but that can actually prevent infection and effectively interrupt the natural transmission cycle. These vaccines should be safely and inexpensively produced, be easy to deliver, and also be capable of inducing lifelong immunity against multiple serotypes and subtypes. Furthermore, there is a need for better integrated strategies that fit the specific needs of endemic regions. Availability of these critical components will greatly enhance the chances for the global control and eradication of FMDV.

Coupled analysis of bacterial transformants and ligation mixture by duplex PCR enables detection of fatal instability of a nascent recombinant plasmid

When a DNA cloning experiment fails, it is often difficult to distinguish between an inadequate cloning protocol and instability of the new recombinant plasmid. The identification of plasmid instability is particularly challenging when the instability is fatal and no DNA of the expected construct can be isolated. We have effectively addressed this problem by employment of duplex PCR (insert-insert, vector-insert) to analyse both the ligation mixture and the resultant bacterial transformants. Using this approach we found a fatal maintenance instability of one of the plasmids generated during subcloning of the cDNA for human LDLR in Escherichia coli STBL2. The described duplex PCR screening method allows monitoring of the fate of nascent recombinant plasmid from ligation, through the initial bacterial colony and the subsequent overnight culture.

Interplay of SOS induction, recombinant gene expression, and multimerization of plasmid vectors in Escherichia coli

Using pBR322- and pUC-derived plasmid vectors, a homologous (Escherichia coli native esterase) and three heterologous proteins (human interleukin-2, human interleukin-6, and Zymomonas levansucrase) were synthesized in E. coli IC2015(recA::lacZ) and GY4786 (sfiA::lacZ) strains. Via time-course measurement of beta-galactosidase activity in each recombinant culture, the SOS induction was estimated in detail and the results were systematically compared. In recombinant E. coli, the SOS response did not happen either with the recombinant insert-negative plasmid backbone alone or the expression vectors containing the homologous gene. Irrespective of gene expression level and toxic activity of synthesized foreign proteins, the SOS response was induced only when the heterologous genes were expressed using a particular plasmid vector, indicating strong dependence on the recombinant gene clone and the selection of a plasmid vector system. It is suggested that in recombinant E. coli the SOS response (i.e., activation of recA expression and initial sfiA expression) may be related neither to metabolic burden nor toxic cellular event(s) by synthesized heterologous protein, but may be provoked by foreign gene-specific interaction between a foreign gene and a plasmid vector. Unlike in E. coli XL1-blue(recA(-)) strains used, all expression vectors encoding each of the three heterologous proteins were multimerized in E. coli IC2015 strains in the course of cultivation, whereas the expression vectors containing the homologous gene never formed the plasmid multimers. The extent of multimerization was also dependent on a foreign gene insert in the expression vector. As a dominant effect of the SOS induction, recombinant plasmid vectors used for heterologous protein expression appear to significantly form various multimers in the recA(+) E. coli host.

Tolerance of Escherichia coli beta-galactosidase C-terminus to different-sized fusions

The tolerance of the beta-galactosidase C-terminus to foreign protein fusions has been explored by using different-sized derivatives of the chimeric protein LACVP1. While the molecular mass of the partner domain shows a minor influence on protein toxicity for the producing E. coli cells, it dramatically affects the proteolytic susceptibility of the whole fusion. Surprisingly, the observed structural modulation of proteolysis is not an all-or-nothing process, but it exhibits a continuous effect concomitantly with the length of the fusion. The conformational effects caused by increasingly sized partners seem to progressively expose cryptic protease target sites, initiating a proteolytic cascade that dramatically reduces the yield of the recombinant protein.

Heat-inactivation of plasmid-encoded CI857 repressor induces gene expression from Ind- lambda prophage in recombinant Escherichia coli

We have observed significant cell lysis upon temperature up-shift of recombinant Escherichia coli cultures harboring CI857-repressed lambda-based expression vectors. This event, that becomes evident about 30-40 min after the heat shock, takes place when using the lambda promoter system in Ind- lysogenic strains, but not in others commonly employed for recombinant gene expression. These results strongly suggest that the thermosensitive CI857 repressor, encoded by the expression vector, competes with CI Ind- molecules for binding to the prophage operator region, allowing for expression of lytic genes from the integrated Ind- viral genome upon temperature up-shift. Transcription of viral lytic genes does not include unspecific expression of a reporter sulA::lacZ gene fusion carried in the prophage genome. These results prompt, however, to carefully evaluate the limitations of expression systems based on pL/pR-CI857 in bacterial strains modified through lambda Ind- gene transfer vehicles.

The expression of recombinant genes from bacteriophage lambda strong promoters triggers the SOS response in Escherichia coli

The production of several non-related heterologous proteins in recombinant Escherichia coli cells promotes a significant transcription of recA and sfiA SOS DNA repair genes. The activation of the SOS system occurs when the expression of plasmid-encoded genes is directed by the strong lambda lytic promoters, but not by IPTG-controlled promoters either at 37 or at 42 degrees C, and it is linked to an extensive degradation of the proteins after their synthesis. The triggering signal for the SOS response could be an important arrest of cell DNA replication observed within the first hour after the induction of recombinant gene expression. The stimulation of this DNA repair system can partially account for the toxicity exhibited by recombinant proteins on actively producing E. coli cells.

A cell adhesion peptide from foot-and-mouth disease virus can direct cell targeted delivery of a functional enzyme

The G-H loop of foot-and-mouth disease virus is a disordered protrusion of the VP1 protein exposed on the virion surface. This short stretch includes an arginine-glycine-aspartic acid tripeptide, a recognized integrin-binding motif, which is responsible for cell attachment and infection. Eight copies of a peptide reproducing the amino acid sequence of this FMDV ligand have been displayed in solvent-exposed regions on an enzymatically active recombinant beta-galactosidase. This viral peptide segment enables the chimeric enzyme to bind mammalian cell lines with different efficiencies, probably depending on the number of suitable cell receptors present on each of them. Moreover, it also promotes the internalization of the attached enzyme, which is transiently active inside the cells. These results suggest further exploration of the potential use of short adhesion peptides of viral origin as cell attachment tags to direct the targeted delivery of both genes and enzymes, instead of whole, infectious viruses.

Insertional mutagenesis in the tailspike protein of bacteriophage P22

The tailspike protein (TSP) of bacteriophage P22 is a homotrimeric multifunctional protein responsible for recognition and hydrolysis of Salmonella typhimurium host receptors. Once properly folded, TSP shows an unusual stability to temperature and detergent denaturation, prompting the analysis of TSP as a framework for the positioning of heterologous protein segments. We have explored the flexibility of inner sites and both amino and carboxy termini to accommodate foreign peptides for phage display. In the examined inner sites, TSP is extremely sensitive to minor sequence modifications, the folding intermediates being rapidly degraded. However, both the amino and carboxy termini are tolerant to peptide fusions, rendering stable and functional chimeric proteins. Surprisingly, the amino terminus, which connects the tail to the neck structure, can accept large peptide fusions, and the foreign amino acid stretches are solvent-exposed and highly antigenic on assembled, infectious virus particles.

A recombinant foot-and-mouth disease virus antigen inhibits DNA replication and triggers the SOS response in Escherichia coli

The 3D gene of foot-and-mouth disease virus encodes the viral RNA dependent RNA polymerase, also called virus infection associated (VIA) antigen, which is the most important serological marker of virus infection. This 3D gene from a serotype C1 virus has been cloned and overexpressed in Escherichia coli under the control of the strong lambda lytic promoters. The resulting 51 kDa recombinant protein has been shown to be immunoreactive with sera from infected animals. After induction of gene expression, an immediate and dramatic arrest of cell DNA synthesis occurs, similar to that produced by genotoxic doses of the drug mitomycin C. This effect does not occur during the production of either a truncated VIA antigen or other related and non-related viral proteins. The inhibition of DNA replication results in a subsequent induction of the host SOS DNA-repair response and in an increase of the mutation frequency in the surviving cells.

Mitomycin C stimulates thermally induced recombinant gene expression in Escherichia coli MC strains

The effects of mitomycin C on C1857-controlled recombinant gene expression have been explored in E. coli cultures when the drug was added simultaneously to the thermal induction. A significantly improved yield of homologous, heterologous and chimeric fusion proteins was observed in E. coli MC1061 and GE864 (a MC4100 derivative) thermoinduced cells. This feature was not detected in other E. coli strains and does not involve a gene dosage mechanism but a strain-dependent stimulation of gene expression unrelated to the RecA protease activity.

Enhanced production of pL-controlled recombinant proteins and plasmid stability in Escherichia coli RecA+ strains

Overexpression of pL-controlled foot-and-mouth disease virus recombinant proteins was studied in Escherichia coli RecA+ strains and in a recA mutant. Higher protein yield and extractable plasmid DNA amounts were found in wild type cells, in absence of detectable RecA proteolytic activity. Minor but still significant differences in pBR322 DNA amounts were also detected between RecA+ and its recA13 and lexA1 derivatives. These data should be seriously considered to select expression systems and to design production processes for recombinant proteins, specially if they are expected to be toxic for Escherichia coli cells.

Uses of beta-galactosidase tag in on-line monitoring production of fusion proteins and gene expression in Escherichia coli

A simple method for monitoring and quantifying automatically the production by fermentation of beta-galactosidase fusion proteins, making use of the remaining activity of the beta-galactosidase part, is considered. A hybrid protein carrying the major antigenic domain of foot-and-mouth disease virus C1 joined at the N-terminus of beta-galactosidase has been expressed in Escherichia coli. The yield of the chimeric protein has been monitored by flow injection analysis (FIA) during batch fermentations at laboratory scale, and a high correlation between values of product concentration from FIA and from immunological quantizations has been obtained. Because of the possibility of employing FIA in large-scale experiments, and the high sampling frequency, versatility, and reproducibility offered by this method, we propose FIA as a general, simple, quick, flexible, and reliable instrument for both monitoring the yield of recombinant proteins produced industrially, and performing basic research at laboratory scale.