Receptor-binding domain of ephrin-A1: production in bacterial expression system and activity.

Eph receptor tyrosine kinases and their ligands, the ephrins, perform an important regulatory function in tissue organization, as well as participate in malignant transformation of cells. Ephrin-A1, a ligand of A class Eph receptors, is a modulator of tumor growth and progression, and the mechanism of its action needs detailed investigation. Here we report on the development of a system for bacterial expression of an ephrin-A1 receptor-binding domain (eA1), a procedure for its purification, and its renaturation with final yield of 50 mg/liter of culture. Functional activity of eA1 was confirmed by immunoblotting, laser scanning confocal microscopy, and flow cytometry. It is shown that monomeric non-glycosylated receptor-binding domain of ephrin-A1 is able to activate cellular EphA2 receptors, stimulating their phosphorylation. Ligand eA1 can be used to study the features of ephrin-A1 interactions with different A class Eph receptors. The created expression cassette is suitable for the development of ligands with increased activity and selectivity and experimental systems for the delivery of cytotoxins into tumor cells that overexpress EphA2 or other class A Eph receptors.

Bacterial production and refolding from inclusion bodies of a "weak" toxin, a disulfide rich protein.

The gene for the "weak" toxin of Naja kaouthia venom was expressed in Escherichia coli. "Weak" toxin is a specific inhibitor of nicotine acetylcholine receptor, but mechanisms of interaction of similar neurotoxins with receptors are still unknown. Systems previously elaborated for neurotoxin II from venom of the cobra Naja oxiana were tested for bacterial production of "weak" toxin from N. kaouthia venom. Constructs were designed for cytoplasmic production of N. kaouthia "weak" toxin in the form of a fused polypeptide chain with thioredoxin and for secretion with the leader peptide STII. However, it became possible to obtain "weak" toxin in milligram amounts only within cytoplasmic inclusion bodies. Different approaches for refolding of the toxin were tested, and conditions for optimization of the yield of the target protein during refolding were investigated. The resulting protein was characterized by mass spectrometry and CD and NMR spectroscopy. Experiments on competitive inhibition of (125)I-labeled alpha-bungarotoxin binding to the Torpedo californica electric organ membranes containing the muscle-type nicotine acetylcholine receptor (alpha1(2)beta1gammadelta) showed the presence of biological activity of the recombinant "weak" toxin close to the activity of the natural toxin (IC(50) = 4.3 +/- 0.3 and 3.0 +/- 0.5 microM, respectively). The interaction of the recombinant toxin with alpha7 type human neuronal acetylcholine receptor transfected in the GH(4)C(1) cell line also showed the presence of activity close to that of the natural toxin (IC(50) 31 +/- 5.0 and 14.8 +/- 1.3 microM, respectively). The developed bacterial system for production of N. kaouthia venom "weak" toxin was used to obtain (15)N-labeled analog of the neurotoxin.

Recombinant human insulin. VIII. Isolation of fusion protein--S-sulfonate, biotechnological precursor of human insulin, from the biomass of transformed Escherichia coli cells.

Various methods have been investigated for the isolation and purification of fusion proteins of precursors of human insulin in the form of S-sulfonates, from the biomass of transformed Escherichia coli cells. Fusion proteins were prepared with different sizes and structures of the leader peptide and the poly-His position (inserted for purification by metal chelate affinity chromatography). The fusion proteins contained an IgG-binding B domain of protein A from Staphylococcus aureus at the N-terminus and an Arg residue between the leader peptide of the molecule and the proinsulin sequence, for trypsin cleavage of the leader peptide. Six residues of Cys in proinsulin allow the chemical modification of the protein as a (Cys-S-SO(-)(3))(6) derivative (S-sulfonate), which increases its polyelectrolytic properties and improves the efficiency of its isolation. Various methods of oxidative sulfitolysis were compared with catalysis by sodium tetrathionate or cystine and Cu2+ or Ni2+ ions. An optimum scheme for the isolation and purification of S-sulfonated fusion proteins was developed by the combination of metal-chelating affinity and ion-exchange chromatography. Highly purified (95%) S-sulfonated fusion protein was recovered which was 85% of the fusion protein contained in the biomass of E. coli cells. Folding of fusion protein S-sulfonate occurred with high yield (up to 90-95%). We found that the fusion protein-S-sulfonate has proinsulin-like secondary structure. This structure causes highly efficient fusion protein folding.

Methods of preparation of recombinant cytokine proteins.

Two schemes for efficient and productive isolation for mutant human recombinant tumor necrosis factor-alpha (TNF-alpha R32H) from Escherichia coli cells were developed. The methods include membrane filtration, ion-exchange chromatography and gel filtration, and centrifugation with subsequent free-flow electrophoresis as an alternative procedure. The target product was obtained as active trimer with total yield more than 50% and greater than 98% purity according to PAGE, size-exclusion chromatography, HPLC, and HPCE.

Recombinant human insulin. VI. Determination of recombinant human proinsulin by capillary zone electrophoresis: optimization of efficiency and selectivity.

The optimization of the separation of recombinant human insulin (rhI) and recombinant human proinsulin (rhP) by free-solution capillary zone electrophoresis in uncoated fused-silica capillaries with ionic and zwitterionic buffers was carried out. The relationship between the selectivity and pH of the buffer was established. The effects of pH and ionic strength of the buffer on protein adsorption on the capillary walls and Taylor diffusion was investigated. The separation of rhI and rhP with an efficiency of 200,000 theoretical plates was achieved using 20 mM Na2HPO4-NaOH buffer (pH 11.2). The proposed method allows the simultaneously determination of rhP and some rhI degradation products (which are also included in pharmacopoeias) in pharmacopoeially limited amounts in rhI.

Recombinant human insulin. V. Optimization of the reversed-phase high-performance liquid chromatographic separation.

The applicability of reversed-phase high-performance liquid chromatography (HPLC) to the analysis of the products of recombinant insulin was studied. The influence of several mobile phases in reversed-phase and ion-pair HPLC on selectivity, resolution and sensitivity was investigated. Optimum conditions for the separation of insulin-related proteins on commercial and laboratory-made supports were established by means of three-dimensional optimizations of selectivity and resolution as a function of pH and ionic strength (mu). A mechanism for the separation of proteins with a mobile phase containing a high salt concentration and a pH near the isoelectric point of proteins is proposed. The questions of scaling up are considered. The proposed techniques allow the analysis of the main impurities and ensures a high quality of active insulin production.

Recombinant human insulin. III. High-performance liquid chromatography and high-performance capillary electrophoresis control in the analysis of step-by-step production of recombinant human insulin.

The production of recombinant human insulin consists of five main stages, accompanied by considerable transformation of molecules, concerning size, secondary structure and the presence of charged groups. The application of different methods, i.e., size-exclusion, ion-exchange and reversed-phase high-performance liquid chromatography (HPLC) and high-performance capillary electrophoresis (HPCE) (capillary zone electrophoresis and micellar electrokinetic capillary chromatography), to the analysis of insulin, insulin-related and non-insulin-related substances was studied. A combined HPLC-HPCE system for the step-by-step control of recombinant human insulin production technology is suggested. The advantages and shortcomings of these methods are discussed.