Boc-Trp(For)-OH

Boc-Trp(For)-OH

Characterization of folded conformations in a tetrapeptide containing two tryptophan residues by vibrational circular dichroism.[Pubmed:19750497]

Chirality. 2009;21 Suppl 1:E76-85.

The intramolecularly hydrogen bonded conformations of the tetrapeptide Boc-Trp-Aib-Gly-Trp-OMe (WUGW) are investigated using experimental and quantum chemical predictions of vibrational circular dichroism (VCD) in the 1800-1550 cm(-1) region. The predicted VCD spectrum, for a conformation (conformer A) obtained from optimization of crystal structure, reproduced the dominant negative VCD band observed experimentally in CH(3)OH and CHCl(3) solvents. However, the predicted VCD spectrum of Conformation A also has an extra positive band which is not seen in the experimental spectra. This mismatch appears to be due to the lack of solvent influence in the quantum chemical geometry optimizations. However, Conformations I and II, obtained, respectively, from constrained optimization of crystal and NMR structures, mimic the solvent stabilized structures and are predicted to have dominant negative VCD band as found in the experimental spectra. It is noted that, for the peptide investigated here, unconstrained quantum chemical geometry optimizations in vacuum converged to structures that are not the realistic models of conformations found in solution. It is also noted that undertaking quantum chemical vibrational property calculations directly using geometries obtained from crystal data or NMR data resulted in unrealistic vibrational frequencies and descriptions. However, constraining the backbone dihedral angles to those found in condensed medium, and optimizing the remaining geometrical parameters resulted in a better reproduction of the observed VCD in condensed medium. The vibrational origins of bands in all of the predicted VCD spectra for the WUGW-tetrapeptide have also been presented.

Neurotensin modulates the electrical activity of frog pituitary melanotropes via activation of a G-protein-coupled receptor pharmacologically related to both the NTS1 and nts2 receptors of mammals.[Pubmed:11146421]

Neuroendocrinology. 2000 Dec;72(6):379-91.

The primary structure of frog neurotensin (fNT) has recently been determined and it has been shown that fNT is a potent stimulator of alpha-MSH secretion by frog pituitary melanotropes. In the present study, we have investigated the effects of fNT on the electrical activity of cultured frog melanotropes by using the patch-clamp technique and we have determined the pharmacological profile of the receptors mediating the effect of fNT. In the cell-attached configuration, fNT (10(-7) M) provoked an increase in the action current discharge followed by an arrest of spike firing. In the gramicidin-perforated patch configuration, fNT (10(-7) M) induced a depolarization accompanied by an increase in action potential frequency and a decrease in membrane resistance. Administration of graded concentrations (10(-10) to 10(-6) M) of fNT or the C-terminal hexapeptide NT(8-13) caused a dose-dependent increase in the frequency of action potentials with EC(50) of 2 x 10(-8) and 5 x 10(-9) M, respectively. The stimulatory effect of fNT was mimicked by various pseudopeptide analogs, with the following order of potency: Boc-[Trp(11)]NT(8-13) > Boc-[D-Trp(11)]NT(8-13) > Boc-[Lys(8,9), Nal(11)]NT(8-13) > Boc-[Psi11,12]NT(8-13). In contrast, the cyclic pseudopeptide analogs of NT(8-13), Lys-Lys-Pro-D-Trp-Ile-Leu and Lys-Lys-Pro-D-Trp-Glu-Leu-OH, did not affect the electrical activity. The NTS1 receptor antagonist and nts2 receptor agonist SR 48692 (10(-5) M) stimulated the spike discharge but did not block the response to fNT. In contrast, SR 142948A (10(-5) M), another NTS1 receptor antagonist and nts2 receptor agonist, inhibited the excitatory effect of fNT. The specific nts2 receptor ligand levocabastine (10(-6) M) had no effect on the basal electrical activity and the response of melanotropes to fNT. In cells which were dialyzed with guanosine-5'-O-(3-thiotriphosphate) (10(-4) M), fNT caused an irreversible stimulation of the action potential discharge. Conversely, dialysis of melanotropes with guanosine-5'-O-(2-thiodiphosphate) (10(-4) M) completely blocked the effect of fNT. Pretreatment of cells with cholera toxin (1 microg/ml) or pertussis toxin (0.2 microg/ml) did not affect the electrical response to fNT. Intracellular application of the G(o/i/s) protein antagonist GPAnt-1 (3 x 10(-5) M) had no effect on the fNT-evoked stimulation. In contrast, dialysis of melanotropes with the G(q/11) protein antagonist GPAnt-2A (3 x 10(-5) M) abrogated the response to fNT. The present data demonstrate that fNT is a potent stimulator of the electrical activity of frog pituitary melanotropes. These results also reveal that the electrophysiological response evoked by fNT can be accounted for by activation of a G(q/11)-protein-coupled receptor subtype whose pharmacological profile shares similarities with those of mammalian NTS1 and nts2 receptors.