SOLUTION STRUCTURE OF PMP-D2, A 35-RESIDUE PEPTIDE ISOLATED FROM THE INSECT, LOCUSTA-MIGRATORIA

The three-dimensional solution structure of PMP-D2, a 35 amino acid pe ptide isolated from the insect Locusta migratoria, has been determined from two-dimensional H-1 NMR spectroscopy data. The structure calcula tions were performed from 222 NOE-derived interproton distances and 11 dihedral angles calculated from the J(HN-H alpha) coupling constants, using either a combination of distance geometry and restrained simula ted annealing or by restrained simulated annealing alone. PMP-D2 conta ins three disulfide bridges that have been assigned from NMR data and structure calculations and independently confirmed using chemical and enzymatic methods. The core region of PMP-D2 adopts a compact globular fold, stabilized by hydrophobic interactions, which consists of a sho rt three-stranded antiparallel P-sheet involving residues 8-11, 15-19, and 25-29. Back-calculation of the NOESY spectra was used to validate the final structures. Analysis of the CD spectra of PMP-D2 under vari ous conditions of ionic strength and in the presence of organic solven ts demonstrates the high stability of this molecule. PMP-D2 was recent ly shown to inhibit Ca2+ currents. This activity is discussed based on the comparison of PMP-D2 three-dimensional structure with the recentl y established three-dimensional structure of the Ca2+ channel blocker omega-conotoxin GVIA.