Z-Gly-Phe-NH2

A number of carbobenzoxy-dipeptide-amides raise the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine (stabilizes the bilayer). The potency of the peptides in stabilizing the bilayer phase is Z-Tyr-Leu-NH2 = Z-Gly-Phe-NH2 greater than Z-Ser-Leu-NH2 greater than Z-Gly-Leu-NH2 greater than Z-Gly-Gly-NH2. A linear correlation was found between the respective HPLC retention time parameter k' for the peptide and the slope of the bilayer stabilization curve determined with model membranes by differential scanning calorimetry. One dipeptide, Z-Ser-Leu-NH2, reduces measles virus cytopathic effect (CPE) in Vero cells. The mechanism by which this peptide reduces the CPE is not known, although some peptides which raise the bilayer to hexagonal phase transition temperature of phospholipids inhibit membrane fusion.

Prior exposure (15 min at 37 degrees C) of several cell types (Vero, SH-SY5Y neuroblastoma, human intestinal epithelial T84) to 3 mm N-benzoyloxycarbonyl-Gly-Phe-amide (Cbz-Gly-Phe-NH(2)), a competitive substrate for metalloendoproteases, completely suppressed cholera toxin (CT)-induced intracellular cAMP accumulation. The specificity of the inhibitory effect was demonstrated by the complete lack of effect of the dipeptide Cbz-Gly-Gly-NH(2), an inactive analogue of Cbz-Gly-Phe-NH(2). The effect was reversible and dose- (IC(50) as low as 0.2 mm depending on the cell type) and time-dependent. Adding Cbz-Gly-Phe-NH(2) during the lag phase caused a diminution of its inhibitory effect similar to that observed with brefeldin A (BFA). Whereas the dipeptide completely suppressed the CT-induced adenylate cyclase (AC) activity, a direct effect on AC is unlikely since the elevation of intracellular cAMP by forskolin was only slightly reduced. The A(1) peptide of CT and NAD(+) activated the AC to the same extent in membranes from control and Cbz-Gly-Phe-NH(2)-treated cells or when Cbz-Gly-Phe-NH(2) was added directly to the assay. The inhibitory effects of suboptimal amounts of Cbz-Gly-Phe-NH(2) and BFA were not additive pointing to a similar mode of action of the two substances. However, Madin-Darby canine kidney cells of which the Golgi structure is BFA-resistant were not resistant to the inhibitory action of Cbz-Gly-Phe-NH(2) on CT cytotoxicity. Several lines of evidence indicate that a perturbation of intracellular Ca(2+) homeostasis by Cbz-Gly-Phe-NH(2) is not responsible for the inhibitory effect of the dipeptide. The dipeptide had also no effect on the binding of (125)I-CT to cells and even increased its intracellular internalization. In contrast with BFA, Cbz-Gly-Phe-NH(2) did not completely suppress the formation of the catalytically active A(1) fragment from bound CT. The data are compatible with a role of metalloendoprotease activity in the intracellular trafficking and processing of CT, although other mechanisms of action of Cbz-Gly-Phe-NH(2) cannot be excluded.

As part of the series investigating the structural features of C-terminal amidated amino acids and peptides, three crystal structures of Z-Gly-Phe-NH2, Tyr-Lys-NH2, and Asp-Phe-NH2 were analyzed by the X-ray diffraction method, and their molecular conformations and intermolecular interactions were investigated. Although the respective dipeptides exhibited an energetically allowable torsion angle concerning each backbone or side chain, the observed extended (Z-Gly-Phe-NH2, Asp-Phe-NH2) and folded (Tyr-Lys-NH2) conformations were considerably different from those of the corresponding unamidated peptides, due to the conformational flexibility of the respective dipeptides. The comparison between the crystal packings of the amidated and unamidated dipeptides indicated that the C-terminal amides tend to associate with the same neighboring group through hydrogen bonds, in which both the amide NH and O=C groups participate, while the unamidated peptides prefer a linear molecular connection, where both or either of the two carboxyl oxygens participate in the hydrogen bond formation. The difference in hydrogen bonding ability between the C-terminal amide and carboxyl groups has been considered to be based on the structural data of the related peptides analyzed so far.