Conformation and calcium binding properties of gastrin fragments of increasing chain length

Solid phase synthesis and conformation of sequential glycosylated polytripeptide sequences related to antifreeze glycoproteins

Sequential glycopeptides [Thr(beta-D-galactose)-Ala-Ala]n, with n ranging from 2 to 7, as models of natural antifreeze glycoproteins were synthesized by the continuous flow, solid phase procedure. The conformational properties of these materials in solution were investigated by c.d. and 1H-n.m.r. spectroscopy. In aqueous solution the c.d. pattern is practically independent of chain length and is very similar to that of natural antifreeze glycoproteins. The results are interpreted in terms of random coil structure. The absence of ordered structures is further confirmed by n.m.r. data. A small amount of ordered conformation can be induced either by increasing the temperature of the aqueous solution or by addition of TFE. The c.d. pattern of all glycopeptides in water at temperatures higher than 50 degrees C are compatible with the presence of a small amount of alpha-helix or 3(10) helix. Since the glyco-hexapeptide is too short to form an alpha-helix, the hypothesis is made that in the glycopeptides in water at high temperature a small amount of 3(10) helix is formed. The same is observed for the 21-residue glycopeptide in presence of 85% (v/v) TFE. In this medium, the c.d. data on the glyco-hexapeptide are more compatible with the presence of a small amount of beta-structure.

Synthesis and 1H-NMR studies of alpha-deuterated analogues of des-Trp1, Nle12-human minigastrin

Three analogues of the tridecapeptide amide H-Leu-(Glu)5-Ala-Tyr-Gly-Nle-Asp-Phe-NH2 were synthetized with alpha-deuterated glutamate residues in specific positions in order to assign unambiguously the 1H nmr spectrum of the parent peptide in water and in water-trifluoroethanol mixtures. The synthetic route is described and the assignment illustrated. A previous, tentative assignment based solely on indirect evidence [Mammi, S., Mammi, N. J. & Peggion, E. (1988) Biochemistry 27, 1374-1379] was partially modified.