A Rubredoxin based system for screening of protein expression conditions and on-line monitoring of the purification process

High yield expression in Pichia pastoris of human neutrophil elastase fused to cytochrome B5

Recombinant human neutrophil elastase (rHNE), a serine protease, was expressed in Pichia pastoris. Glycosylation sites were removed via bioengineering to prevent hyper-glycosylation (a common problem with this system) and the cDNA was codon optimized for translation in Pichia pastoris. The zymogen form of rHNE was secreted as a fusion protein with an N-terminal six histidine tag followed by the heme binding domain of Cytochrome B5 (CytB5) linked to the N-terminus of the rHNE sequence via an enteropeptidase cleavage site. The CytB5 fusion balanced the very basic rHNE (pI = 9.89) to give a colored fusion protein (pI = 6.87), purified via IMAC. Active rHNE was obtained via enteropeptidase cleavage, and purified via cation exchange chromatography, resulting in a single protein band on SDS PAGE (Mr = 25 KDa). Peptide mass fingerprinting analysis confirmed the rHNE amino acid sequence, the absence of glycosylation and the absence of an 8 amino acid C-terminal peptide as opposed to the 20 amino acids usually missing from the C-terminus of native enzyme. The yield of active rHNE was 0.41 mg/L of baffled shaker flask culture medium. Active site titration with alpha-1 antitrypsin, a potent irreversible elastase inhibitor, quantified the concentration of purified active enzyme. The Km of rHNE with methoxy-succinyl-AAPVpNA was identical with that of the native enzyme within the assay's limit of accuracy. This is the first report of full-length rHNE expression at high yields and low cost facilitating further studies on this major human neutrophil enzyme.

Identification of FAM181A and FAM181B as new interactors with the TEAD transcription factors

The Hippo pathway is a key signaling pathway in the control of organ size and development. The most distal elements of this pathway, the TEAD transcription factors, are regulated by several proteins, such as YAP (Yes-associated protein), TAZ (transcriptional co-activator with PDZ-binding motif) and VGLL1-4 (Vestigial-like members 1-4). In this article, combining structural data and motif searches in protein databases, we identify two new TEAD interactors: FAM181A and FAM181B. Our structural data show that they bind to TEAD via an Ω-loop as YAP/TAZ do, but only FAM181B possesses the LxxLF motif (x any amino acid) found in YAP/TAZ. The affinity of different FAM181A/B fragments for TEAD is in the low micromolar range and full-length FAM181A/B proteins interact with TEAD in cells. These findings, together with a recent report showing that FAM181A/B proteins have a role in nervous system development, suggest a potential new involvement of the TEAD transcription factors in the development of this tissue.

An improved strategy for easy process monitoring and advanced purification of recombinant proteins

In this work, a multifunctional expression cassette, termed Multitags, combining different and complementary functionalities, was designed and used to monitor the expression and the purification of two model proteins (Pfu DNA polymerase and Myosin-VIIa- and Rab-Interracting protein : MyRIP). Multitags contains two affinity purification tags, a polyhistidine sequence (10× His) and the streptavidin-binding peptide (SBP) and as a marker tag the heme-binding domain of rat cytochrome b5 followed by the TEV cleavage site. Using the Multitags as fusion partner, more than 90 % of both fusion proteins were produced in soluble form when expressed in Escherichia coli KRX. In addition, high purity (99 %) of recombinant proteins was achieved after two consecutive affinity purification steps. The expression cassette also demonstrated an accurate monitoring capability comparable to that of a dual recognition-based method. The choice of the SBP tag was considered as an integral process that included a method for tag removal. Thus, an immobilized TEV protease fixed on streptavidin-agarose matrix was used for the cleavage of fusion proteins. After digestion, both unprocessed fusion proteins and Multitags were retained on the proteolytic column via their SBP sequence, allowing cleavage and recovery of target proteins on one step. This combined approach may accelerate the development of optimized production processes, while insuring high product quality and a low production cost.

One-step generation of error-prone PCR libraries using Gateway® technology

Background

Error-prone PCR (epPCR) libraries are one of the tools used in directed evolution. The Gateway^® technology allows constructing epPCR libraries virtually devoid of any background (i.e., of insert-free plasmid), but requires two steps: the BP and the LR reactions and the associated E. coli cell transformations and plasmid purifications.

Results

We describe a method for making epPCR libraries in Gateway^® plasmids using an LR reaction without intermediate BP reaction. We also describe a BP-free and LR-free sub-cloning method for in-frame transferring the coding sequence of selected clones from the plasmid used to screen the library to another one devoid of tag used for screening (such as the green fluorescent protein). We report preliminary results of a directed evolution program using this method.

Conclusions

The one-step method enables producing epPCR libraries of as high complexity and quality as does the regular, two-step, protocol for half the amount of work. In addition, it contributes to preserve the original complexity of the epPCR product.

Positive-selection vector for direct protein expression

We describe the development of a novel positive-selection vector, RHP-AmpS, that is suitable for seamless cloning and high-level protein expression in Escherichia coli. In this vector, beta-lactamase (Bla) was rendered nonfunctional by replacing the codon for the C-terminal amino acid of the beta-lactamase gene (bla) with a stop codon. Insertion of a target gene in the correct orientation (tail to tail) results in the reconstruction of the C-terminal codon (W290) of bla. This restores the function of the gene and allows the selection of positive recombinants on agar plates containing ampicillin. To allow a high level of protein expression, this selection cassette was inserted into the T7 polymerase-based expression cassette of the Novagen pET28a expression vector. To our knowledge, this is the first example of true positive-selection cloning and direct, high-level expression from a single vector.

Optimization of protein expression systems for modern drug discovery

The expression of high levels of stable and functional proteins remains a bottleneck in many scientific endeavors, including the determination of structures in a high-throughput fashion or the screening for novel active compounds in modern drug discovery. Recently, numerous developments have been made to improve the production of soluble and active proteins in heterologous expression systems. These include modifications to the expression constructs, the introduction of new and/or improved pro- and eukaryotic expression systems, and the development of improved cell-free protein synthesis systems. The introduction of robotics has enabled a massive parallelization of expression experiments, thereby vastly increasing the throughput and, hopefully, the output of such experiments. In addition, the big challenges of recombinant overexpression of membrane and secreted proteins are tackled, and some new methods are reviewed.

High level expression of peptides and proteins using cytochrome b5 as a fusion host

A novel fusion protein system based on the highly soluble heme-binding domain of cytochrome b5 has been designed. The ability of cytochrome b5 to increase the levels of expression and solubility of target proteins has been tested by expressing several proteins and peptides, viz., alpha hemoglobin stabilizing protein, the regulatory subunits of acetohydroxy acid synthase I (ilvM) and II (ilvN), the carboxy terminal domains of mouse neuronal kinesin and pantothenate synthatase, two peptide toxins from cone snails, and the inactivation gate from the brain voltage gated sodium channel, NaV1.2. The fusion protein system has been designed to incorporate protease cleavage sites for commonly used proteases, viz., enterokinase, Factor Xa, and Tobacco etch virus protease. Accumulation of expressed protein as a function of time may be visually ascertained by the fact that the cells take on a bright red color during the course of induction. In all the cases tested so far, the fusion protein accumulates in the soluble fraction to high levels. A novel purification protocol has been designed to purify the fusion proteins using metal affinity chromatography, without the need of a hexahistidine-tag. Mass spectral analysis has shown that the fusion proteins are of full length. CD studies have shown that the solubilized fusion proteins are structured. The proteins of interest may be cleaved from the parent protein by either chemical or enzymatic means. The results presented here demonstrate the versatility of the cytochrome b5 based fusion system for the production of peptides and small proteins (<15 kDa).