The Solution Structure of a Monocyclic Analog of Endothelin [1,15 Aba]-ET-1, Determined by 1H NMR Spectroscopy

• Published in: Journal of medicinal chemistry 1994-03, Vol.37 (5), p.656-664
• Main Authors: Coles, Murray, Munro, Sharon L. A, Craik, David J
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Aminoacids, peptides. Hormones. Neuropeptides; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Endothelin-1 - analogs & derivatives; Endothelins - chemistry; Fundamental and applied biological sciences. Psychology; Hydrogen Bonding; Magnetic Resonance Spectroscopy; Molecular Sequence Data; Protein Conformation; Protein Structure, Secondary; Proteins; Solutions
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm00031a016

The structure of [1,15 Aba]-ET-1 has been determined in aqueous acetonitrile solution (10% acetonitrile, 1.5% acetic acid). [1,15 Aba]-ET-1 is an analogue of endothelin (ET-1) in which the disulfide bridge linking residues 1 and 15 has been removed by replacement of the cysteine residues with the mimicking group alpha-aminobutyric acid (Aba). The structure has been determined by 1H NMR spectroscopy and simulated annealing calculations based on NOE constraints, 3JHN-H alpha scalar coupling constants, and amide-proton-exchange rates. Distance information was extracted from 2D NOESY spectra using full-relaxation matrix techniques (utilizing the program DISCON). The structure can be described in terms of three defined segments: a type I beta-turn over residues 5-8, a helix over residues 9-16, and a structured C-terminus over residues 17-21. The data indicate that some conformational averaging occurs throughout the peptide, particularly for residues 1-4 in the N-terminus, where no preferred conformation is present. The structure is compared with those previously reported for native ET-1. In general, removal of the disulfide bridge does not cause a major structural change in the helical and turn regions of the sequence, but increased structural disorder is noted at the N-terminus. The implications of the monocyclic analogue's conformation for the pharmacological activity and the ETA/ETB selectivity of the endothelin family of peptides and analogues are described. The N-terminus is proposed to be a key structural region for differentiation of binding activity at the ETA and ETB receptor sites.