SOLUTION STRUCTURE OF HUMAN CALCITONIN GENE-RELATED PEPTIDE BY H-1-NMR AND DISTANCE GEOMETRY WITH RESTRAINED MOLECULAR-DYNAMICS

The structure of human calcitonin gene-related peptide 1 (hCGRP-1) has been determined by H-1 NMR in a mixed-solvent system of 50% trifluoroethanol/50% H2O at pH 3.7 and 27-degrees-C. Complete resonance assignment was achieved by using two-dimensional methods. Distance restraints for structure calculations were obtained by semiquantitative analysis of intra- and interresidue nuclear Overhauser effects; in addition, stereospecific or chi-1 rotamer assignments were obtained for certain side chains. Structures were generated from the distance restraints by distance geometry, followed by refinement using molecular dynamics, and were compared with experimental NH-C-alpha-H coupling constants and amide hydrogen exchange data. The structure of hCGRP-1 in this solvent comprises an amino-terminal disulfide-bonded loop (residues 2-7) leading into a well-defined alpha-helix between residues 8 and 18; thereafter, the structure is predominantly disordered, although there are indications of a preference for a turn-type conformation between residues 19 and 21. Comparison of spectra for the homologous hCGRP-2 with those of hCGRP-1 indicates that the conformations of these two forms are essentially identical.