Conformations of prostaglandin F 2alpha and recognition of prostaglandins by their receptors.

The conformation of prostaglandin F 2alpha (PGF 2alpha) has been determined by x-ray diffraction techniques. Two independent conformers of PGF 2alpha, studied as the tris(hydroxymethyl)methylamine salt, are observed to adopt the familiar "hairpin" conformation with the alpha and omega chains aligned roughly parallel. The conformers differ in ring conformation and at the C(17)-C(18) bond, one adopting a C(9) envelope ring conformation and a trans geometry at the C(17)-C(18) bond, while the other adopts a C(8) envelope ring conformation and a novel gauche geometry about C(17)-C(18). Comparison of the conformation of PGF 2alpha with that of prostaglandin E2 suggests a recognition mechanism which would permit PGF 2alpha and prostaglandin E receptors to distinguish between the two potent prostaglandins. The recognition model explains much of the binding data for the PGF 2alpha receptor in the corpus luteum and predicts the existence of an interesting PGF 2alpha analog.