Conformations of prostaglandin F_2α and recognition of prostaglandins by their receptors

The conformation of prostaglandin F_2α, (PGF _2α) has been determined by x-ray diffraction techniques. Two independent conformers of PGF_2α, studied as the tris(hydroxymethyl)methylamine salt, are observed to adopt the familiar "hairpin" conformation with the α and ω 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_2α with that of prostaglandin E₂ suggests a recognition mechanism which would permit PGF_2α, and prostaglandin E receptors to distinguish between the two potent prostaglandins. The recognition model explains much of the binding data for the PGF _2α receptor in the corpus luteum and predicts the existence of an interesting PGF_2α analog.