Bacterial expression of a natively folded extracellular domain fusion protein of the hFSH receptor in the cytoplasm of Escherichia coli

Single-Step Protocol for Isolating the Recombinant Extracellular Domain of the Luteinizing Hormone Receptor from the Ovis aries Testis

The luteinizing hormone receptor (LHR) is a glycoprotein member of the G protein-coupled receptors superfamily. It participates in corpus luteum formation and ovulation in females and acts in testosterone synthesis and spermatogenesis in males. In this study, we extracted RNA from sheep testicles and synthetized the cDNA to amplify the gene lhr-bed. This gene consists of 762 bp and encodes 273 amino acids of the extracellular domain of LHR. The lhr-bed was cloned into pJET1.2/blunt, then subcloned into pCOLD II, and finally, transformed in E. coli BL21 (DE3) cells. Because the induced rLHR-Bed protein was found in the insoluble fraction, we followed a modified purification protocol involving induction at 25 °C, subjection to denaturing conditions, and on-column refolding to increase solubility. We confirmed rLHR-Bed expression by means of Western blot and mass spectrometry analysis. It is currently known that the structure stem-loop 5′UTR on pCOLD II vector is stable at 15 °C. We predicted and obtained RNAfold stability at 25 °C. We successfully obtained the recombinant LHR extracellular domain, with protein yields of 0.2 mg/L, and purity levels of approximately 90%, by means of a single chromatographic purification step. The method described here may be used to obtain large quantities of rLHR-Bed in the future.

Discovery of a mammalian splice variant of myostatin that stimulates myogenesis

Myostatin plays a fundamental role in regulating the size of skeletal muscles. To date, only a single myostatin gene and no splice variants have been identified in mammals. Here we describe the splicing of a cryptic intron that removes the coding sequence for the receptor binding moiety of sheep myostatin. The deduced polypeptide sequence of the myostatin splice variant (MSV) contains a 256 amino acid N-terminal domain, which is common to myostatin, and a unique C-terminus of 65 amino acids. Western immunoblotting demonstrated that MSV mRNA is translated into protein, which is present in skeletal muscles. To determine the biological role of MSV, we developed an MSV over-expressing C₂C₁₂ myoblast line and showed that it proliferated faster than that of the control line in association with an increased abundance of the CDK2/Cyclin E complex in the nucleus. Recombinant protein made for the novel C-terminus of MSV also stimulated myoblast proliferation and bound to myostatin with high affinity as determined by surface plasmon resonance assay. Therefore, we postulated that MSV functions as a binding protein and antagonist of myostatin. Consistent with our postulate, myostatin protein was co-immunoprecipitated from skeletal muscle extracts with an MSV-specific antibody. MSV over-expression in C₂C₁₂ myoblasts blocked myostatin-induced Smad2/3-dependent signaling, thereby confirming that MSV antagonizes the canonical myostatin pathway. Furthermore, MSV over-expression increased the abundance of MyoD, Myogenin and MRF4 proteins (P<0.05), which indicates that MSV stimulates myogenesis through the induction of myogenic regulatory factors. To help elucidate a possible role in vivo, we observed that MSV protein was more abundant during early post-natal muscle development, while myostatin remained unchanged, which suggests that MSV may promote the growth of skeletal muscles. We conclude that MSV represents a unique example of intra-genic regulation in which a splice variant directly antagonizes the biological activity of the canonical gene product.

Recombinant production of human interleukin 6 in Escherichia coli

In this study, we compared basic expression approaches for the efficient expression of bioactive recombinant human interleukin-6 (IL6), as an example for a difficult-to-express protein. We tested these approaches in a laboratory scale in order to pioneer the commercial production of this protein in Escherichia coli (E. coli). Among the various strategies, which were tested under Research and Development (R&D) conditions, aggregation-prone IL6 was solubilized most effectively by co-expressing cytoplasmic chaperones. Expression of a Glutathion-S-Transferase (GST) fusion protein was not efficient to increase IL6 solubility. Alteration of the cultivation temperature significantly increased the solubility in both cases, whereas reduced concentrations of IPTG to induce expression of the T7lac-promotor only had a positive effect on chaperone-assisted expression. The biological activity was comparable to that of commercial IL6. Targeting the expressed protein to an oxidizing environment was not effective in the generation of soluble IL6. Taken together, the presence of chaperones and a lowered cultivation temperature seem effective to isolate large quantities of soluble IL6. This approach led to in vivo soluble, functional protein fractions and reduces purification and refolding requirements caused by downstream purification procedures. The final yield of soluble recombinant protein averaged approximately 2.6 mg IL6/liter of cell culture. These findings might be beneficial for the development of the large-scale production of IL6 under the conditions of current good manufacturing practice (cGMP).

Single chain human chorionic gonadotropin, hCGalphabeta: effects of mutations in the alpha subunit on structure and bioactivity

The strategy of translationally fusing the subunits of heterodimeric proteins into single chain molecules is often used to overcome the mutagenesis-induced defects in subunit interactions. The approach of fusing the alpha and beta subunits of human Chorionic Gonadotropin (hCG) to produce a single chain hormone (phCGalphabeta) was used to investigate roles of critical residues of the alpha subunit in hormone receptor interaction and biological activity. The alpha subunit was mutated using PCR-based site-directed mutagenesis, fused to the wild type beta subunit and the fusion protein was expressed using Pichia pastoris expression system. Following partial purification, the mutant proteins were extensively characterized using immunological probes, receptor assays, and in vitro bioassays. The mutation hCGalpha P38A, which disrupts subunit interaction in the heterodimeric molecule, produced a fusion molecule exhibiting altered subunit interactions as judged by the immunological criteria, but could bind to the receptor with lower affinity and elicit biological response. Mutation of hCGalpha T54A disrupting the glycosylation at Asparagine 52, believed to be important for bioactivity, also yielded a biologically active molecule suggesting that the glycosylation at this site is not as critical for bioactivity as it is in the case of the heterodimer. The fusion protein approach was also used to generate a superagonist of hormone action. Introduction of four lysine residues in the Loop 1 of the alpha subunit led to the generation of a mutant having higher affinity for the receptor and enhanced bioactivity. Immunological characterization of single chain molecules revealed that the interactions between the subunits were not identical to those seen in the heterodimeric hormone, and the subunits appeared to retain their isolated conformations, and also retained the ability to bind to the receptors and elicit response. These data suggest the plasticity of the hormone-receptor interactions.

A strategy for high-level expression of soluble and functional human interferon alpha as a GST-fusion protein in E. coli

Escherichia coli is the most extensively used host for the production of recombinant proteins. However, most of the eukaryotic proteins are typically obtained as insoluble, misfolded inclusion bodies that need solubilization and refolding. To achieve high-level expression of soluble recombinant human interferon alpha (rhIFNalpha) in E. coli, we have first constructed a recombinant expression plasmid (pGEX-hIFNalpha2b), in which we merged the hIFNalpha2b cDNA with the glutathione S-transferase (GST) coding sequence downstream of the tac-inducible promoter. Using this plasmid, we have achieved 70% expression of soluble rhIFNalpha2b as a GST fusion protein using E. coli BL21 strain, under optimized environmental factors such as culture growth temperature and inducer (IPTG) concentration. However, release of the IFN moiety from the fusion protein by thrombin digestion was not optimal. Therefore, we have engineered the expression cassette to optimize the amino acid sequence at the GST-IFN junction and to introduce E. coli preferred codon within the thrombin cleavage site. We have used the engineered plasmid (pGEX-Delta-hIFNalpha2b) and the modified E. coli trxB(-)/gor(-) (Origami) strain to overcome the problem of removing the GST moiety while expressing soluble rhIFNalpha2b. Our results show the production of soluble and functional rhIFNalpha2b at a yield of 100 mg/l, without optimization of any step of the process. The specific biological activity of the purified soluble rhIFNalpha2b was equal to 2.0 x 10(8) IU/mg when compared with the WHO IFNalpha standard. Our data are the first to show that high yield production of soluble and functional rhIFNalpha2b tagged with GST can be achieved in E. coli.

cDNA cloning and functional expression of jerdostatin, a novel RTS-disintegrin from Trimeresurus jerdonii and a specific antagonist of the alpha1beta1 integrin

Jerdostatin represents a novel RTS-containing short disintegrin cloned by reverse transcriptase-PCR from the venom gland mRNA of the Chinese Jerdons pit viper Trimeresurus jerdonii. The jerdostatins precursor cDNA contained a 333-bp open reading frame encoding a signal peptide, a pre-peptide, and a 43-amino acid disintegrin domain, whose amino acid sequence displayed 80% identity with that of the KTS-disintegrins obtustatin and viperistatin. The jerdostatin cDNA structure represents the first complete open reading frame of a short disintegrin and points to the emergence of jerdostatin from a short-coding gene. The different residues between jerdostatin and obtustatin/viperistatin are segregated within the integrin-recognition loop and the C-terminal tail. Native jerdostatin (r-jerdostatin-R21) and a R21K mutant (r-jerdostatin-K21) were produced in Escherichia coli. In each case, two conformers were isolated. One-dimensional (1)H NMR showed that conformers 1 and 2 of r-jerdostatin-R21 represent, respectively, well folded and unfolded proteins. The two conformers of the wild-type and the R21K mutant inhibited the adhesion of alpha(1)-K562 cells to collagen IV with IC(50) values of 180 and 703 nm, respectively. The IC(50) values of conformers 2 of r-jerdostatin-R21 and r-jerdostatin-K21 were, respectively, 5.95 and 12.5 microm. Neither r-jerdostatin-R21 nor r-jerdostatin-K21 showed inhibitory activity toward other integrins, including alpha(IIb)beta(3), alpha(v)beta(3), alpha(2)beta(1), alpha(5)beta(1), alpha(4)beta(1), alpha(6)beta(1), and alpha(9)beta(1) up to a concentration of 24 mum. Although the RTS motif appears to be more potent than KTS inhibiting the alpha(1)beta(1) integrin, r-jerdostatin-R21 is less active than the KTS-disintegrins, strongly suggesting that substitutions outside the integrin-binding motif and/or C-terminal proteolytic processing are responsible for the decreased inhibitory activity.

Identification of a Functional Epitope of the Nogo Receptor by a Combinatorial Approach Using Ribosome Display

The Nogo receptor (NgR) plays a central role in mediating growth-inhibitory activities of myelin-derived proteins, thereby severely limiting axonal regeneration after injury of the adult mammalian central nervous system (CNS). The inhibitory proteins Nogo, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp) all bind to the extracellular leucine-rich repeat (LRR) domain of NgR, which provides a large molecular surface for protein-protein interactions. However, epitopes within the LRR domain of NgR for binding Nogo, MAG and OMgp have not yet been revealed. Here, we report an evolutionary approach based on the ribosome display technology for detecting regions involved in ligand binding. By applying this method of "affinity fingerprinting" to the NgR ligand binding domain we were able to detect a distinct region important for binding to Nogo. Several residues defining the structural epitope of NgR involved in interaction with Nogo were subsequently confirmed by alanine scanning mutagenesis.

Ribosome display of mammalian receptor domains

Many mammalian receptor domains, among them a large number of potential therapeutic target proteins, are highly aggregation-prone upon heterologous expression in bacteria. This severely limits functional studies of such receptor domains and also their engineering towards improved properties. One of these proteins is the Nogoreceptor, which plays a central role in mediating the inhibition of axon growth and functional recovery after injury of the adult mammalian central nervous system. We show here that the ligand binding domain of the Nogoreceptor folds to an active conformation in ternary ribosomal complexes, as formed in ribosome display. In these complexes the receptor is still connected, via a C-terminal tether, to the peptidyl tRNA in the ribosome and the mRNA also stays connected. The ribosome prevents aggregation of the protein, which aggregates as soon as the release from the ribosome is triggered. In contrast, no active receptor was observed in phage display, where aggregation appears to prevent incorporation of the protein into the phage coat. This strategy sets the stage for rapidly studying defined mutations of such aggregation-prone receptors in vitro and to improve their properties by in vitro evolution using the ribosome display technology.