STRUCTURE COMPARISON OF THE PHEROMONES ER-1, ER-10, AND ER-2 FROM EUPLOTES-RAIKOVI

The NMR structures of the homologous pheromones Er-1, Er-10, and Er-2 from the ciliated protozoan Euplotes raikovi are compared. For all 3 p roteins the molecular architecture is made up of an antiparallel 3-hel ix bundle. The preservation of the core part of the structure is direc tly manifested by similar patterns of slowed backbone amide proton exc hange rates, hydrogen bond formation, and relative solvent accessibili ty. To align the 6 half-cystine residues in the individual sequences w ithin the preserved 3-dimensional core structure, several deletions an d insertions had to be introduced that differ from those previously pr oposed on the basis of the primary structures. Of special interest is a deletion in the second helix of Er-2, which is accommodated by a tra nsition from an alpha-helix in Er-1 and Er-10 to a 3(10)-helix in Er-2 . The most significant structural differences are located in the C-ter minal part of the proteins, which may have an important role in specif ic receptor recognition.