SOLUTION STRUCTURE OF HUMAN CALCITONIN IN MEMBRANE-MIMETIC ENVIRONMENT - THE ROLE OF THE AMPHIPATHIC HELIX

The 32 amino acid hormone human calcitonin was studied at pH 3.7 and 7 .4 by multidimensional NMR spectroscopy in sodium dodecyl sulfate mice lles at 310K. The secondary structure was obtained from nuclear Overha user enhancement spectroscopy (NOESY), (3)JHN(alpha) coupling constant s, and slowly exchanging amide data. Three-dimensional structures cons istent with NMR data were generated by using distance geometry calcula tions. A set of 265 interproton distances derived from NOESY experimen ts, hydrogen-bond constraints obtained from amide exchange, and coupli ng constants were used. From the initial random conformations, 30 dist ance geometry structures with minimal violations were selected for fur ther refinement with restrained energy minimization. In micelles, at b oth pus, the hormone assumes an amphipathic alpha-helix from Leu9 to P he16, followed by a type-I beta-turn between residues Phe16 and Phe19. From His20 onward the molecule is extended and no interaction with th e helix was observed, The relevance of the amphipathic helix for the s tructure-activity relationship, the possible mechanisms of interaction with the receptor, as well as the formation of fibrillar aggregates, is discussed, Proteins 32:314-323, 1998, (C) 1998 Wiley-Liss, Inc.