THE NMR SOLUTION STRUCTURE OF THE PHEROMONE ER-11 FROM THE CILIATED PROTOZOAN EUPLOTES-RAIKOVI

The NMR solution structure of the pheromone Er-11, a 39-residue protei n from the ciliated protozoan Euplotes raikovi, was calculated with th e distance geometry program DIANA from 449 NOE upper distance constrai nts and 97 dihedral angle constraints, and the program OPAL was employ ed for structure refinement by molecular mechanics energy minimization in a water bath. For a group of 20 conformers used to characterize th e solution structure, the average of the pairwise RMS deviations from the mean structure calculated for the backbone heavy atoms N, C-alpha, and C' of residues 2-38 was 0.30 Angstrom. The molecular architecture is dominated by an up-down-up bundle of three short helices with resi dues 2-9, 12-19, and 22-32, which is closely similar to the previously determined structures of the homologous pheromones Er-1, Er-2, and Er -10. This finding provides structural evidence for the capability show n by these pheromones to compete with each other in binding reactions to their cell-surface receptors.