A new solid-phase synthesis of porcine vasoactive intestinal peptide using Nα-9-fluorenylmethyloxycarbonyl amino acids

Vasoactive intestinal polypeptide precursors have highly potent bronchodilatory activity

We studied the structure-activity relationships of vasoactive intestinal polypeptide (VIP) to determine whether there were active forms of C-terminal-free VIP, so that suitable structures could be identified and produced by recombinant technology. We found that some presumptive VIP precursors prepared by solid-phase synthesis exhibited a higher biological activity than natural VIP both in vitro and in vivo, although we could not determine the actual active fragment. VIP-Gly-Lys-OH and VIP-Gly-Lys-Arg-OH, which were extended from the C-terminal of mature VIP, demonstrated a respective 210% and 160% increase in bronchodilatory activity in comparison to the activity of natural VIP. Furthermore, these peptides exhibited a respective 110% and 130% increase in hypotensive activity when compared with VIP itself.

Solid phase peptide synthesis utilizing 9-fluorenylmethoxycarbonyl amino acids

9-Fluorenylmethoxycarbonyl (Fmoc) amino acids were first used for solid phase peptide synthesis a little more than a decade ago. Since that time, Fmoc solid phase peptide synthesis methodology has been greatly enhanced by the introduction of a variety of solid supports, linkages, and side chain protecting groups, as well as by increased understanding of solvation conditions. These advances have led to many impressive syntheses, such as those of biologically active and isotopically labeled peptides and small proteins. The great variety of conditions under which Fmoc solid phase peptide synthesis may be carried out represents a truly "orthogonal" scheme, and thus offers many unique opportunities for bioorganic chemistry.

Synthesis, cloning and expression in Escherichia coli of artificial genes coding for biologically active elongated precursors of the vasoactive intestinal polypeptide

Synthetic genes coding for elongated precursors of the vasoactive intestinal polypeptide (VIP) were synthesized and cloned in a highly efficient Escherichia coli expression vector. The synthetic genes code for VIP with its methionine (at position 17) replaced by leucine and elongated at the C-terminus by Gly (vasoactive intestinal polypeptide-Gly, i.e. VIPa) or by Gly-Lys-Arg (vasoactive intestinal polypeptide-Gly-Lys-Arg, i.e. VIPb). The synthetic genes fused to the N-terminal part of the E. coli beta-galactosidase gene were expressed to yield high amounts of fusion proteins reaching upon induction at least 60% of the total cellular protein. The fusion proteins of 314 and 316 amino acids carrying in their C-terminal portion either the 29 or 31 amino acids long VIP precursor polypeptide were shown to be immunoreactive with VIP antisera and were further purified and cleaved by CNBr. The resulting purified peptide precursors (VIPa and VIPb) were recognized by VIP receptors in rat liver plasma membranes and by antibodies to porcine VIP in a radioimmunoassay. Both precursors activated adenylate cyclase in rat liver membranes and stimulated pancreatic secretion in the cat. The affinity and potency of the cloned precursors is close to that of VIP purified from porcine intestine, suggesting that the elongated VIP precursors may act even without being converted into the C-terminal amide form of the peptide. The elongated VIP precursors expressed in E. coli may provide a cheap, large-scale source of experimental material for studies on VIP actions.

Synthesis, conformational studies and biological activities of VIP and related fragments

VIP and related fragments were prepared by the solid-phase method. The peptides were assembled on a benzhydrylamine resin and couplings of the Boc-amino acids were carried out by the symmetrical anhydride method. Cleavage was achieved by treatment with liquid HF and purification was accomplished by successive steps of cation exchange, partition and semi-preparative high pressure liquid chromatography. The biological activities were evaluated in vitro in the rabbit perfused heart and in vivo on the rat blood pressure. Structural studies were performed by high resolution (400 MHz) 1H-NMR spectroscopy and circular dichroism. The results show that among all the fragments tested, only VIP2-28 retains significant biological activity. The fragments 1-14 and 15-28, which are devoid of activity, were found to be inactive as antagonists. VIP and some of the fragments tend to adopt the helical structure, as demonstrated by spectroscopic techniques.