The tunable pReX expression vector enables optimizing the T7-based production of membrane and secretory proteins in E. coli.

BACKGROUND: To optimize the production of membrane and secretory proteins in Escherichia coli, it is critical to harmonize the expression rates of the genes encoding these proteins with the capacity of their biogenesis machineries. Therefore, we engineered the Lemo21(DE3) strain, which is derived from the T7 RNA polymerase-based BL21(DE3) protein production strain. In Lemo21(DE3), the T7 RNA polymerase activity can be modulated by the controlled co-production of its natural inhibitor T7 lysozyme. This setup enables to precisely tune target gene expression rates in Lemo21(DE3). The t7lys gene is expressed from the pLemo plasmid using the titratable rhamnose promoter. A disadvantage of the Lemo21(DE3) setup is that the system is based on two plasmids, a T7 expression vector and pLemo. The aim of this study was to simplify the Lemo21(DE3) setup by incorporating the key elements of pLemo in a standard T7-based expression vector. RESULTS: By incorporating the gene encoding the T7 lysozyme under control of the rhamnose promoter in a standard T7-based expression vector, pReX was created (ReX stands for Regulated gene eXpression). For two model membrane proteins and a model secretory protein we show that the optimized production yields obtained with the pReX expression vector in BL21(DE3) are similar to the ones obtained with Lemo21(DE3) using a standard T7 expression vector. For another secretory protein, a c-type cytochrome, we show that pReX, in contrast to Lemo21(DE3), enables the use of a helper plasmid that is required for the maturation and hence the production of this heme c protein. CONCLUSIONS: Here, we created pReX, a T7-based expression vector that contains the gene encoding the T7 lysozyme under control of the rhamnose promoter. pReX enables regulated T7-based target gene expression using only one plasmid. We show that with pReX the production of membrane and secretory proteins can be readily optimized. Importantly, pReX facilitates the use of helper plasmids. Furthermore, the use of pReX is not restricted to BL21(DE3), but it can in principle be used in any T7 RNAP-based strain. Thus, pReX is a versatile alternative to Lemo21(DE3).

Optimizing E. coli-Based Membrane Protein Production Using Lemo21(DE3) or pReX and GFP-Fusions.

Optimizing the conditions for the production of membrane proteins in E. coli is usually a laborious and time-consuming process. Combining the Lemo21(DE3) strain or the pReX T7-based expression vector with membrane proteins C-terminally fused to Green Fluorescent Protein (GFP) greatly facilitates the optimization of membrane protein production yields. Both Lemo21(DE3) and pReX allow precise regulation of expression intensities of genes encoding membrane proteins, which is critical to identify the optimal production condition for a membrane protein. The use of GFP-fusions allows direct monitoring and visualization of membrane proteins at any stage during the production optimization process.

High-level production of membrane proteins in E. coli BL21(DE3) by omitting the inducer IPTG.

BACKGROUND: For membrane protein production, the Escherichia coli T7 RNA polymerase (T7 RNAP)-based protein production strain BL21(DE3) in combination with T7-promoter based expression vectors is widely used. Cells are routinely cultured in Lysogeny broth (LB medium) and expression of the chromosomally localized t7rnap gene is governed by the isopropyl-ß-D-1-thiogalactopyranoside (IPTG) inducible lacUV5 promoter. The T7 RNAP drives the expression of the plasmid borne gene encoding the recombinant membrane protein. Production of membrane proteins in the cytoplasmic membrane rather than in inclusion bodies in a misfolded state is usually preferred, but often hampered due to saturation of the capacity of the Sec-translocon, resulting in low yields. RESULTS: Contrary to expectation we observed that omission of IPTG from BL21(DE3) cells cultured in LB medium can lead to significantly higher membrane protein production yields than when IPTG is added. In the complete absence of IPTG cultures stably produce membrane proteins in the cytoplasmic membrane, whereas upon the addition of IPTG membrane proteins aggregate in the cytoplasm and non-producing clones are selected for. Furthermore, in the absence of IPTG, membrane proteins are produced at a lower rate than in the presence of IPTG. These observations indicate that in the absence of IPTG the Sec-translocon capacity is not/hardly saturated, leading to enhanced membrane protein production yields in the cytoplasmic membrane. Importantly, for more than half of the targets tested the yields obtained using un-induced BL21(DE3) cells were higher than the yields obtained in the widely used membrane protein production strains C41(DE3) and C43(DE3). Since most secretory proteins reach the periplasm via the Sec-translocon, we also monitored the production of three secretory recombinant proteins in the periplasm of BL21(DE3) cells in the presence and absence of IPTG. For all three targets tested omitting IPTG led to the highest production levels in the periplasm. CONCLUSIONS: Omission of IPTG from BL21(DE3) cells cultured in LB medium provides a very cost- and time effective alternative for the production of membrane and secretory proteins. Therefore, we recommend that this condition is incorporated in membrane- and secretory protein production screens.

Low-dose prednisone inclusion in a methotrexate-based, tight control strategy for early rheumatoid arthritis: a randomized trial.

BACKGROUND: Treatment strategies for tight control of early rheumatoid arthritis (RA) are highly effective but can be improved. OBJECTIVE: To investigate whether adding prednisone, 10 mg/d, at the start of a methotrexate (MTX)-based treatment strategy for tight control in early RA increases its effectiveness. DESIGN: A 2-year, prospective, randomized, placebo-controlled, double-blind, multicenter trial (CAMERA-II [Computer Assisted Management in Early Rheumatoid Arthritis trial-II]). (International Standard Randomised Controlled Trial Number: ISRCTN 70365169) SETTING: 7 hospitals in the Netherlands. PATIENTS: 236 patients with early RA (duration <1 year). INTERVENTION: Patients were randomly assigned to an MTX-based, tight control strategy starting with either MTX and prednisone or MTX and placebo. Methotrexate treatment was tailored to the individual patient at monthly visits on the basis of predefined response criteria aiming for remission. MEASUREMENTS: The primary outcome was radiographic erosive joint damage after 2 years. Secondary outcomes included response criteria, remission, and the need to add cyclosporine or a biologic agent to the treatment. RESULTS: Erosive joint damage after 2 years was limited and less in the group receiving MTX and prednisone (n = 117) than in the group receiving MTX and placebo (n = 119). The MTX and prednisone strategy was also more effective in reducing disease activity and physical disability, achieving sustained remission, and avoiding the addition of cyclosporine or biologic treatment. Adverse events were similar in both groups, but some occurred less in the MTX and prednisone group. LIMITATION: A tight control strategy for RA implies monthly visits to an outpatient clinic, which is not always feasible. CONCLUSION: Inclusion of low-dose prednisone in an MTX-based treatment strategy for tight control in early RA improves patient outcomes. PRIMARY FUNDING SOURCE: Catharijne Foundation.