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Conformation-Activity Relationship of Tachykinin Neurokinin A (4- 10) and of Some [ Xaa8] Analogues Gabriella Saviano,t Piero Andrea Temussi,*3t Andrea Motta,s Carlo Albert0 Maggi) and Paolo Roveroll Dipartimento di Chimica, Universith di Napoli, Via Mezzocannone 4, 801 34 Napoli, Italy, ICMIB del CNR, Via Toiano 6, Arco Felice, Napoli, Italy, and Menarini Ricerche, Via Sette Santi 3, Firenze, Italy Received March 18, 1991; Revised Manuscript Received June 27, 1991 ABSTRACT: NKA(4-lo), 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 @-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/H20 cryoprotective mixture combined with internal energy calculations. NKA(4-10) is characterized by a structure containing a type I @-turnextending from SerS to Gly8, followed by a y-turn centered on Gly8, whereas for [/3-Ala8]NKA(4-10) is possible to suggest a type I @-turn extending from Ser' to @-Ala8, followed by a C8 turn comprising @-Ala8 and Leug and by another 0-turn extending from /3-Ala8 to the terminal NH2. The preferred conformation of [P-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, 117-1201. The preferred solution conformation of [@-Ala8]NKA(4-10) may thus be considered as a likely bioactive conformation for NK-2 selective peptides. Neurokinin A (NKA)~ is a neuropeptide of sequence His-Lys-Thr-Asp-Ser-Phe-Val-Gly-Leu-Met-NH2, expressed by mammalian neurons (Kimura et al., 1983; Kanagawa et al., 1983) in the same precursor, y-preprotachykinin A (Nawa et al., 1983), containing the sequences of substance P (SP) and neurokinin B (NKB). The wide spectrum of action of NKA and its potential usefulness in the field of antiasthmatic * zyxwvutsrqponmlkjih Universiti di Napoli. 8 ICMlB del CNR. Menarini Ricerche. 0006-2960/91/0430-10175$02.50/0 drugs (Nawa et al., 1984) has stimulated many structure- activity relationship (SAR) investigations (Dion et al., 1987a; Abbreviations: Aib, three-letter code for aminoisobutyric acid; 8- Ala, &alanine; BFGS, Broyden-Fletcher-Goldfarb-Shanno algorithm; DMSO-$, perdeuteriodimethyl sulfoxide; DQF-COSY, double-quan- tum-filtered correlation spectroscopy; EM, energy minimization calcu- lations; GABA, y-aminobutyric acid; GPI, guinea pig ileum; NK-1, substance P receptor; NK-2, NKA receptor; NK-3, NKB receptor; NKA, neurokinin A; NKB, neurokinin B; NOE, nuclear Overhauser effect; NOESY, nuclear Overhauser effect spectroscopy; RPA, rabbit pulmo- nary artery; RPV, rat portal vein; SAR, structureactivity relationship; SP, substance P TMS, tetramethylsilane. 0 1991 American Chemical Society