Conformation-activity relationship of tachykinin neurokinin A(4-10) and of some [Xaa8] analogs

Abstract

NKA (4-10), the C-terminal heptapeptide fragment (Asp-Ser-Phe-Val-Gly-Leu-Met-NH2) of tachykinin NKA, is more active than the parent native compound in the interaction with the NK-2 receptor. Substitution of Gly8 with the more flexible residue beta-Ala8 increases its selectivity with respect to other two known receptors (NK-1 and NK-3), whereas substitution with either D-Ala8 or GABA8 deprives the peptide of its biological activity. These findings can be interpreted by a conformational analysis based on NMR studies in DMSO-d6 and in a DMSO-d6/H2O cryoprotective mixture combined with internal energy calculations. NKA(4-10) is characterized by a structure containing a type I beta-turn extending from Ser5 to Gly8, followed by a gamma-turn centered on Gly8, whereas for [beta-Ala8]NKA(4-10) is possible to suggest a type I beta-turn extending from Ser5 to beta-Ala8, followed by a C8 turn comprising beta-Ala8 and Leu9 and by another beta-turn extending from beta-Ala8 to the terminal NH2. The preferred conformation of [beta-Ala8]NKA(4-10) is not compatible with models for NK-1 and NK-3 agonists proposed on the basis of rigid peptide agonists [Levian-Teitelbaum et al. (1989) Biopolymers 28, 51-64; Sumner & Ferretti (1989) FEBS Lett. 253, 117-120]. The preferred solution conformation of [beta-Ala8]NKA(4-10) may thus be considered as a likely bioactive conformation for NK-2 selective peptides.

Solution conformation of c‐[Gln‐Trp‐Phe‐Gly‐Leu‐Met], a NK‐2 tachykinin antagonist

“…This arrangement is close to that of the side chains of Phe-Val in the p-turn conformation proposed (8) for the bioactive conformation of the potent agonist [P-Ala8]-NKA (4-lo), whereas the side chains of the sequence Leu-Met are forced, by cyclization constraints, to occupy a region of space quite different from that of the corresponding residues in the quoted agonist. The structure sets including conformers (1, 2, 3), (7,8,9) and (11,12) show great similarities among their members and can be grouped into families. An interesting feature of these structures is the presence of significant topological similarities that, in turn, allow a possible connection in terms of conformational domains.…”

“…Accordingly, we chose to measure NOESY spectra in a (90:10, v:v) DMSO-d6/H2O cryoprotective mixture at 280 K, an experimen-tal condition that can favor the selection of ordered conformations (5)(6)(7)(8). The computational procedure can be divided into two steps: (i) an EM calculation is performed, using a quasi-Newton method, the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, stopping when the gradient norm is 10 -or less; (ii) a final refinement is obtained by a full Newton-Raphson minimization, with a convergence criterium on the gradient norm of 10or less.…”

“…The combination of a DMSO/water cryoprotective mixture (4) and low temperature, as expected from previous conformational studies on bioactive peptides (5)(6)(7)(8), favors the selection of ordered conformations, while thc use of a complete, albeit coarse, conformational search may overcome some pitfalls of MD calculations. The main causes of this discrepancy can be traced to the use of a different solvent and 556 to a different treatment of the data.…”

Conformational studies of tachykinin peptides using NMR spectroscopy

“…Keeping the above in mind, we would like to stress that our results have provided evidence for the folded structure of ScyI in DMSO. The conformations obtained, although different from those published for selective agonists of the NK-1 and NK-2 tachykinin receptors, also revealed certain similarities, in particular with the proposed bioactive conformation of the selective NK-2 agonist [fl-AlaS]NKB(4-10) [6]. On the other hand, the conformational flexibility of the fragment Leu-Met-NH2 is believed to be required for the selectivity of the ligands towards the NK-1 tachykinin receptor [7].…”

MEN 11420 (Nepadutant), a novel glycosylated bicyclic peptide tachykinin NK2 receptor antagonist

“…In our search for potent and selective tachykinin NK 2 receptor antagonists, we speculated that a common conformational feature should be present in NK 2 receptor agonists, such as [βAla 8 ]NKA(4–10) (Saviano et al , 1991), and certain peptide‐derived antagonists, such as the cyclic hexapeptide L‐659–877 (cyclo(Leu‐Gln‐Tpr‐Phe‐Gly‐Met), Williams et al , 1988; Giolitti & Maggi, 1994). From molecular modelling studies we postulated that a β‐turn around the Trp‐Phe segment would be important for high affinity ligand‐receptor interaction: on this basis, a conformational constraint which could lock the hypothetically active conformation in the monocyclic NK 2 receptor antagonist L‐659–877 was designed (Pavone et al , 1995a,b).…”