[Biotechnological production of acetylated thymosin beta4].

Thymosin beta4 (43 aa) is a highly conserved acidic peptide which regulates actin polymerization in mammalian cells by sequestering globular actin. Thymosin beta4 is undergoing clinical trials as a drug for the treatment of venous stasis ulcers, corneal wounds and injuries, as well as acute myocardial infarction. Currently, thymosin beta4 is produced with solid-phase chemical synthesis. Biotechnological synthesis of this peptide presents difficulties because N-terminal amino acid residue of thymosin beta4 is acetylated. In this study we propose a method for producing the recombinant precursor of thymosin beta4 and its subsequent targeted chemical acetylation. Desacetylthymosin beta4 was synthesized as a part of a hybrid protein with thioredoxin and a specific TEV (tobacco etch virus) protease cleavage site. The following scheme was developed for the purification of desacetylthymosin beta4: (i) the biosynthesis of a soluble hybrid protein (HP) in Escherichia coli; (ii) isolation of the HP by ion exchange chromatography; (iii) cleavage of the HP with TEVprotease; (iv) purification of desacetylthymosin beta4 by ultra-filtration. N-terminal acetylation of desacetylthymosin beta4 was performed with acetic anhydride under acidic conditions (pH 3). The reaction yield was 55%. Thymosin beta4 was then purified by reverse-phase high performance liquid chromatography. The proposed synthetic approach to recombinant thymosin beta4 is suitable for scale-up and can provide for the medical use of highly purified preparation with a yield of 20 mg from 1 L of culture.

Expression and hydroxylamine cleavage of thymosin alpha 1 concatemer.

Human thymosin alpha 1 (Talpha1) is an important peptide in the development and senescence of immunological competence in human, and many studies have reported the expression of this peptide. In this study, we designed and synthesized the Talpha1 gene according to the E. coli codon usage preference and constructed a 6xTalpha1 concatemer. The latter was inserted into an E. coli expression vector pET-22b (+), and transformed into E. coli BL21 (DE3). After induction with IPTG, the concatemer protein was successfully expressed in E. coli then cleaved by hydroxylamine to release the Talpha1 monomer. Gly-SDS-PAGE and mass spectrometry confirmed that the recombinant protein was cleaved as intended. The bioactivity of the Talpha1 monomer was analyzed by lymphocyte proliferation and by mitochondrial activity in two different tumor cell lines. This study provides a description of the preparation of a bioactive Talpha1, which may prove useful in future biomedical research.

On the molecular size of thymosins.

The immunoregulatory polypeptide prothymosin alpha and its biologically active N-terminal fragment thymosin alpha 1m, with relative molecular masses of 12,500 and 3108 respectively, were found to behave as oligomers (trimers to hexamers) in gel-filtration measurements. This phenomenon of an apparent association of polypeptides has been reported for other thymosins--parathymosin alpha, thymosin beta 4 and thymosin beta 10. In contrast, sedimentation equilibrium ultracentrifugation shows that thymosin alpha 1 is a monomer with a relative molecular mass of 3000 +/- 200. Measurement of the diffusion coefficient as 221 micron2/s suggests that the molecule is approximately spherical. The implications for the molecular species of prothymosin alpha, parathymosin alpha, and beta-thymosins are discussed.

Radioimmunoassays for the C-terminus of prothymosin alpha and the N-terminus of parathymosin alpha for the measurement of the levels of alpha-thymosins in human cancer.

A radioimmunoassay specific for the C-terminus of human prothymosin alpha was developed using the synthetic peptide [Cys-Aca degrees]-human prothymosin alpha (90-109)-OH coupled to KLH as antigen and the analogue [Tyr-Aca degrees]-human prothymosin alpha (90-109)-OH labelled with 125I as tracer. The radioimmunoassay measured intact prothymosin alpha, in the range of 2-100 pmol and does not cross-react with the partly homologous polypeptide parathymosin alpha. A major epitope was located in the segment 95-107. A radioimmunoassay specific for the N-terminus of human parathymosin alpha, also measuring intact parathymosin alpha in the range of 1-20 pmol and not cross-reacting with prothymosin alpha, was developed using the synthetic peptide [Cys-Aca degrees]-human parathymosin alpha (1-30)-OH as antigen coupled to KLH and the analogue [Tyr-Aca degrees]-human parathymosin alpha (1-10)-OH labelled with 125I as tracer. A major epitope was located in the segment 1-10. These radioimmunoassays, together with a previously established radioimmunoassay for the N-terminus of prothymosin alpha, permitted the identification of the molecular forms of the cross-reactive materials in both normal and neoplastic breast tissue extracts as intact prothymosin alpha and parathymosin alpha. It was also possible to reveal significantly higher levels of both alpha-thymosins in breast cancer tissue compared to the nearby healthy tissue--the mean of 14 samples was over 14-fold higher--suggesting a role of both prothymosin alpha and parathymosin alpha in cell proliferation. The reported radioimmunoassays are expected to facilitate the search for prognostic and/or diagnostic applications of these polypeptides in human cancer.

Thymosin-like peptides as potential immunostimulants. Synthesis via the polymeric-reagent method.

This paper reports our attempt at designing new immunostimulating peptides which are chemically related to the bioactive peptides thymosin alpha 1 and thymopentin. Three peptides were synthesized, Asp-Leu-Lys-Glu-Arg-Lys-Asp-Val-Tyr (3), Arg-Lys-Asp-Val-Tyr-Glu-Glu-Ala-Glu-Asn (2), and Asp-Leu-Lys-Glu-Arg-Lys-Asp-Val-Tyr-Glu-Glu-Ala-Glu-Asn (1), each of which contains the thymopentin sequence and portions of the bioactive sequence of thymosin alpha 1. Peptides 1-3 were assembled from selected blocked fragments that were synthesized by the polymeric-reagent method, using PHBT (polystyrene-bound 1-hydroxybenzotriazole) as the activating polymer. The ability of peptides 1-3 to enhance the activation (RNA synthesis) and proliferation (DNA synthesis) of human T lymphocytes was determined. In comparison to thymosin alpha 1, thymosin alpha 1 (15-28), and thymopentin, peptides 1-3 did not show significant enhancement of these processes.

Thymosin alpha 1: biological activities, applications and genetic engineering production.

Thymosin alpha 1 (Tα1), a 28-amino acid peptide, was first described and characterized from calf thymuses in 1977. This peptide can enhance T-cell, dendritic cell (DC) and antibody responses, modulate cytokines and chemokines production and block steroid-induced apoptosis of thymocytes. Due to its pleiotropic biological activities, Tα1 has gained increasing interest in recent years and has been used for the treatment of various diseases in clinic. Accordingly, there is an increasing need for the production of this peptide. So far, Tα1 used in clinic is synthesized using solid phase peptide synthesis. Here, we summarize the genetic engineering methods to produce Tα1 using prokaryotic or eukaryotic expression systems. The effectiveness of these biological products in increasing the secretion of cytokines and in promoting lymphocyte proliferation were investigated in vitro studies. This opens the possibility for biotechnological production of Tα1 for the research and clinical applications.

Optimized Fmoc solid-phase synthesis of Thymosin alpha1 by side-chain anchoring onto a PEG resin.

Thymosin alpha1 is a 28-amino acid acetylated peptide used for the treatment of hepatitis B and C. This peptide has a difficult sequence because of the presence of consecutive beta-branched amino acids and shows a tendency to form beta-sheet structures, partly as a result of the many protecting groups required to assemble the peptide (up to 20 side-chain protecting groups). Consequently, its synthesis has been generally achieved by convergent solution chemistry. Here we report a straightforward stepwise solid-phase synthesis on a polyethylene glycol solid-support that enables the scaling-up of this key therapeutic peptide.

4-Methoxybenzyloxycarbonyl amino acids in solid phase peptide synthesis.

Moz-amino acids were used in solid-phase synthesis of Leu-Ala-Gly-Val and thymosin alpha 1. It was found that the Moz-group can be removed rapidly and completely with 5-10% TFA in CH2Cl2. Some advantages of utilizing Moz-amino acids over Boc-amino acids in solid phase peptide synthesis are demonstrated.

Structure, solubility and reactivity of peptides. A conformational study of two protected key intermediates from a large-scale synthesis of thymosin alpha 1.

A conformational study of two protected peptide segments, (1-10 and 11-28), spanning the entire sequence of thymosin alpha 1, in solvents of different polarity and capability of forming hydrogen bonds, is reported. By using infrared absorption and circular dichroism techniques the occurrence of the random coil conformation, the self-associated beta-structure, and the alpha-helix (the latter adopted only by the longer peptide) was established. The self-associated species of the two peptide segments were disrupted either by adding increasing amounts of hexamethylphosphoramide or by dilution. This structural transition was monitored by the disappearance of the amide-I C = O stretching band of strongly intermolecularly hydrogen-bonded molecules (near 1630 cm-1) in the infrared absorption spectra. The tendency of these peptides to aggregate is paralleled by a decrease in their solubility. The conformational findings are discussed in terms of the solvent-dependent product yields obtained in the reaction of segment (1-10) with the N alpha-deprotected (11-28) segment to give the fully protected thymosin alpha 1.

Synthesis of thymosin alpha 1 by fragment condensation using tert.-butyl side chain protection.

A novel synthesis of thymosin alpha 1 by classical methods using seven tert.-butyl side chain protected fragments is described. Optimum conditions were found for the final DCC/HOBt coupling of the two key intermediates; decapeptide and octadecapeptide. Thymosin alpha 1 was purified by two stages of preparative HPLC (partial purification with C8 and final purification with C18 reverse phase silica gel) to give a 30% overall yield for the final four stages of synthesis (including catalytic hydrogenation of octadecapeptide, coupling, deprotection and purification). The product was shown to be homogeneous by thin-layer and paper high voltage electrophoresis, isoelectric focusing analysis, thin-layer chromatography and high performance liquid chromatography. Amino acid analysis, optical rotation, 1H-n.m.r. spectroscopy, FAB mass spectroscopy and peptide mapping after tryptic digestion confirmed the structure of thymosin alpha 1. Three minor stereoisomer contaminants were isolated by HPLC and characterized as [D-Lys14]-thymosin alpha 1, [D-Lys17]-thymosin alpha 1 and [D-Ala3]-thymosin alpha 1 resulting from racemization at Lys14, Lys17 and Ala3 during the coupling of the fragments. A final contaminant, isolated by HPLC, was characterized as N alpha-isobutyloxycarbonyl-thymosin alpha 1 (15-28), which results from "wrong way opening" of an activated mixed anhydride.

Synthesis of the C-terminal half of thymosin alpha 1 by the polymeric reagent method.

In this report we further show the utility and efficiency of polymer-bound 1-hydroxybenzotriazole (PHBT) as an almost ideal support for the polymeric reagent method of peptide synthesis. This was demonstrated by the synthesis of thymosin alpha 1 (15-28), in which two suitably blocked segments, Boc-Asp (OtBu)-Leu-Lys (2Cz)-Glu (OBzl)-Lys (2Cz)-Lys (2Cz)-OH (3) and Boc-Glu (OBzl)-Val-Val-Glu (OBzl)-Glu (OBzl)-Ala-Glu (OBzl)-Asn-OBzl (2), were prepared entirely by utilizing PHBT activation for each coupling step. After appropriate deblocking of 2, segments 2 and 3 were coupled by the DCC-HOBT method, followed by complete deblocking and ion-exchange chromatographic purification, affording the C-terminal half of thymosin alpha 1, H-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH (1).

Solid-phase synthesis of thymosin alpha 1 using tert-butyloxycarbonylaminoacyl-4-(oxymethyl)phenylacetamidomethyl-resin.

Thymosin alpha 1 and its desacetyl analogue were synthesized by the solid-phase method. Use of aminoacyl-4-(oxymethyl)phenylacetamidomethyl-resin resulted in an improved yield and allowed the synthetic products to be purified by simple ion-exchange and gel filtration chromatography. Success of the synthesis was largely due to enhanced stability of the peptide-resin linkage to trifluoroacetic acid and to the elimination of hydroxy functions on the resin. This improved quality of the solid support helps eliminate chain loss and chain termination during the synthesis. The purified synthetic peptides were found to be homogeneous by paper electrophoresis, isoelectric focusing in polyacrylamide gel, and thin-layer chromatography. They also had biological activity in the azathioprine-sensitive rosette assay. Use of the new 9-(2-sulfo)fluorenylmethyloxycarbonyl chloride reagent for purification of protected peptides was also demonstrated and discussed.

Effects of synthetic thymosin beta 9 fragments on low E-rosette-forming cells of lupus nephritis patients.

Five fragments from hexapeptide to decapeptide, corresponding to positions 16-25 of thymosin beta 9, were synthesized and their effects on low E-rosette-forming capacity with sheep erythrocytes of cells from lupus nephritis patients were compared with that of the undecapeptide (positions 16-26) of thymosin beta 9 by taking synthetic thymosin beta 9 as a standard. Two of the fragments (16-25 and 18-25) exhibited higher activity than that of the parent peptide (16-26). The other three sequences (17-25, 19-25, and 20-25) had no effect at concentrations as high as 10(-4) M.

The synthesis of peptides with potential thymic hormone activity: the synthesis of endo-Arg38a-deacetylthymosin beta 10.

A tritetracontapeptide corresponding to the entire amino acid sequence of endo-Arg38a-deacetylthymosin beta 10 was synthesized by a conventional solution method. Seven peptide fragments were assembled, followed by deprotection with 1 M trifluoromethanesulfonic acid-thioanisole-Me2Se in trifluoroacetic acid. In preliminary experiments the synthetic tritetracontapeptide increased the entire peripheral T-cell population and a helper T-cell subset when incubated in vitro with blood which was obtained from a uremic patient with pneumonia, but a suppressor/cytotoxic T-cell subset was unaffected under these conditions. The synthetic endo-Arg38a-deacetylthymosin beta 10 was as active as synthetic deacetylthymosin beta 10 in this in vitro assay.

Solid phase synthesis of thymosin beta 9.

Thymosin beta 9, a 41 residue thymic polypeptide, has been synthesized by a solid phase method. A modification of the low HF method was used to deprotect and cleave the peptide from the resin. Thymosin beta 9 was then obtained in analytically pure form by a one-step purification procedure in 32% yield. The activity of thymosin beta 9 in the terminal deoxynucleotidyl transferase assay was greater than calf thymus fraction 5, but comparable to thymosin beta 4. In contrast to thymosin alpha 1, neither beta 4 nor beta 9 was active in the rosette inhibition assay.

Syntheses of two deacetyl-thymosin beta4 analogs and their anti-inflammatory effect on carrageenin-induced edema in the mouse paw.

Two [Met(0)6]deacetyl-thymosin beta4 analogs containing Phe(4F) or Tyr(Me) at position 12 were synthesized by the manual solid-phase method, and their anti-inflammatory effect on carrageenin-induced edema in the mouse paw was studied. Fluorination of the para-position of Phe12 resulted in a marked antiinflammatory effect on carrageenin-induced edema in the mouse paw compared with that of our synthetic [Met(0)6]deacetyl-thymosin beta4, but the other analog, [Met(0)6, Tyr(Me)12]deacetyl-thymosin beta4, showed a marked reduction of the anti-inflammatory effect.

Thymosin beta 4 (Fx peptide) is a potent regulator of actin polymerization in living cells.

Thymosin beta 4 (beta 4) is a 5-kDa polypeptide originally identified in calf thymus. Although numerous activities have been attributed to beta 4, its physiological role remains elusive. Recently, beta 4 was found to bind actin in human platelet extracts and to inhibit actin polymerization in vitro, raising the possibility that it may be a physiological regulator of actin assembly. To examine this potential function, we have increased the cellular beta 4 concentration by microinjecting synthetic beta 4 into living epithelial cells and fibroblasts. The injection induced a diminution of stress fibers and a dose-dependent depolymerization of actin filaments as indicated by quantitative image analysis of phalloidin binding. Our results show that beta 4 is a potent regulator of actin assembly in living cells.

Synthesis of prothymosin alpha deduced from nucleotide sequence of the murine cDNA and its effect on the impaired T lymphocytes of uremic patients.

The complete murine prothymosin alpha molecule (110 residues) except for the N-terminal methionine deduced from the cloned cDNA has been synthesized by a solid-phase method. Peptide synthesis was performed manually by the stepwise solid-phase method using the base-labile Fmoc group for protecting the alpha-amino group. The peptide was assembled on a p-alkoxybenzyl alcohol resin. After the last coupling step, the Fmoc group was removed with 50% piperidine in DMF. The peptide resin was treated with thioanisole-o-cresol in TFA, and then purified by gel filtration, ion-exchange column chromatography and high-performance liquid chromatography. A 2.9-mg sample of a highly purified peptide was finally obtained. The overall yield of the synthesis was less than 1%, based on the amino acid content of the starting Fmoc-Asp (OtBu)-resin. The synthetic peptide was found to have a restoring activity on low-E-rosette-forming lymphocytes after incubation of peripheral blood from uremic patients with the synthetic peptide. This peptide exhibited far stronger restoring effect than that of our synthetic thymosin alpha 1.

Synthesis of rat parathymosin alpha fragment 1-28 and examination of its inhibitory activity towards the restoring activity of thymosin alpha 1 on the impaired T-lymphocytes of uremic patients.

A fragment corresponding to N-terminal octaeicosapeptide of rat parathymosin alpha was synthesized by assembling 5 peptide fragments, followed by deprotection with 1 M trifluoromethanesulfonic acid-thioanisole (molar ratio 1:1) in trifluoroacetic acid in the presence of dimethylselenium. Incubation of impaired T-lymphocytes isolated from uremic patients with the synthetic parathymosin alpha fragment 1-28 showed no immunological restoring effect, but when it was administered together with thymosin alpha 1, it appeared to suppress the restoring effect of the thymosin alpha 1 on the impaired T-lymphocytes of uremic patients.

Solid-phase synthesis of biologically active fragment 29-111 of rat prothymosin alpha.

Rat prothymosin alpha fragment 29-111, an 83-residue polypeptide corresponding to desthymosin alpha 1-prothymosin alpha, has been synthesized by a solid-phase method. Hydrogen fluoride was used to deprotect and cleave the peptide from the resin. The crude product was purified by gel-filtration, ion-exchange chromatography and high-performance liquid chromatography. A 3.2-mg sample of a ca. 96% pure peptide was finally obtained. The overall yield of the synthesis was less than 1%. An increase of E-rosette-forming lymphocytes was obtained after incubation of peripheral blood from uremic patients with the synthetic prothymosin alpha fragment 29-111. The restoring effect of the synthetic prothymosin alpha fragment 29-111 was greater than that of our synthetic thymosin alpha 1.