Synthesis and biological activity of N-terminal-truncated derivatives of human epidermal growth factor (h-EGF)

Effect of Molecular Size of PEGylated Recombinant Human Epidermal Growth Factor on the Biological Activity and Stability in Rat Wound Tissue

The purpose of this study was to investigate the effect of size of polyethylene glycol (PEG) conjugated to recombinant human epidermal growth factor (rhEGF) on its stability in skin wound tissue and in vitro biological activity to find the desirable conjugate as topical therapeutic agent for wound healing. Site-specific PEGylation at N-terminus of rhEGF was performed with monomethoxy PEG-Butyraldehyde derivatives (MW 2, 5, and 20 kDa). Mono-PEG-rhEGFs retained 60-70% of biological activity of native rhEGF, and the effect of PEG size was not significant. The improvement of stability in the rat skin wound tissue was dependent on the increase of the PEG size attached. The degradation half-lives of native rhEGF, mono-PEG-2K-, -5K-, and -20K-rhEGFs were 1.1, 3.1, 5.2, and 41.5 hr, respectively. Therefore, mono-PEG-20K-rhEGF was considered to be the most desirable in terms of the increase of stability and the preservation of biological activity. This study suggests that the high molecular weight PEG at N-terminus of rhEGF would give a satisfactory stabilizing effect and thus may improve therapeutic efficacy in clinical use.

Expression of recombinant human epidermal growth factor in Escherichia coli and characterization of its biological activity

Recombinant human epidermal growth factor (EGF) was successfully expressed as a fusion protein in Escherichia coli system. This system was used OmpA signal sequence to produce soluble protein into the periplasm of E. coli. Human EGF (hEGF) synthesized in bacterial cell was found to be similar in size with the original protein and molecular weight approximately at 6.8 kDa. Cell proliferation assay was conducted to characterize the biological activity of hEGF on human dermal fibroblasts. The synthesized hEGF was found to be functional as compared with authentic hEGF in stimulating cell proliferation and promoting growth of cell. In comparison of biological activity between synthesized and commercial hEGF on cell proliferation, the results showed there was no significant different. This finding indicates the synthesized hEGF in E. coli system is fully bioactive in vitro.

The role of disulfide bonds in the structure and function of murine epidermal growth factor (mEGF)

A systematic study using solid phase peptide synthesis has been undertaken to examine the role of the disulfide bonds in the structure and function of mEGF. A combination of one, two and three native disulfide pair analogues of an active truncated (4-48) form of mEGF have been synthesised by replacing specific cysteine residues with isosteric a-amino-n-butyric acid (Abu). Oxidation of the peptides was performed using either conventional aerobic oxidation at basic pH, in DMSO under acidic conditions or via selective disulfide formation using orthogonal protection of the cysteine pairs. The contribution of individual, or pairs of, disulfide bonds to EGF structure was evaluated by CD and (1)H-NMR spectroscopy. The mitogenic activity of each analogue was determined using Balb/c 3T3 mouse fibroblastsAs we have reported previously (Barnham et al. 1998), the disulfide bond between residues 6 and 20 can be removed with significant retention of biological activity (EC50 20-50 nM). The overall structure of this analogue was similar to that of native mEGF, indicating that the loss of the 6-20 disulfide bridge did not affect the global fold of the molecule. We now show that removal of any other disulfide bond, either singly or in pairs, results in a major disruption of the tertiary structure, and a large loss of activity (EC50>900 nM). Remarkably, the linear analogue appears to have greater activity (EC50 580 nM) than most one and two disulfide bond analogues although it does not have a definable tertiary structure.

Isolation and structure determination of a paralytic peptide from the hemolymph of the silkworm, Bombyx mori

A peptide with paralytic activity in larvae of the silkworm, Bombyx mori, was isolated from its hemolymph. Purification procedures consisted of extraction with 50% acetone, Vydac C4 reversed-phase cartridge elution and 4 steps of reversed-phase HPLC. Injection of the purified peptide into 4th instar B. mori larvae caused rapid and rigid paralysis for 2 min at a dose of 3.4 ng/larva. This paralytic peptide consists of 23 amino acid residues containing 2 cysteines with an intra-disulfide bond. The complete amino acid sequence is: H-Glu-AsnPhe-Val-Gly-Gly-Cys-Ala-Thr-Gly-Phe-Lys-Arg-Thr-Ala-Asp-G ly-Arg-Cys-Lys-Pro-Thr-Phe-OH. The relationship between structure and the biologic activity of synthetic analogs indicated that the entire amino acid sequence and the intra-disulfide bond were necessary for biological activity.