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 peptide isolated from the insect Locusta migratoria, has been determined from two-dimensional 1H NMR spectroscopy data. The structure calculations were performed from 222 NOE-derived interproton distances and 11 dihedral angles calculated from the JHN-H alpha coupling constants, using either a combination of distance geometry and restrained simulated annealing or by restrained simulated annealing alone. PMP-D2 contains 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 short three-stranded antiparallel beta-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 various conditions of ionic strength and in the presence of organic solvents demonstrates the high stability of this molecule. PMP-D2 was recently shown to inhibit Ca2+ currents. This activity is discussed based on the comparison of PMP-D2 three-dimensional structure with the recently established three-dimensional structure of the Ca2+ channel blocker omega-conotoxin GVIA.