Complete amino acid sequences of follitropin and lutropin in the ostrich, Struthio camelus.

We determined the complete amino acid sequences of two pituitary gonadotropins, follitropin and lutropin in the ostrich, thereby providing the first information on the structure of avian follitropin. Ostrich follitropin and lutropin both consist of two subunits: a common alpha-subunit and a hormone-specific beta-subunit. The alpha-subunit is composed of 96 amino acid residues and has 70-80% sequence identity with the alpha-subunits of most vertebrates. The ostrich follitropin beta-subunit consists of 106 amino-acid residues, and shows 70-74% sequence identity with mammalian follitropins beta, 61% with amphibian follitropin beta, 39-46% with teleost gonadotropins II beta and 32-44% with teleost gonadotropins I beta. The ostrich lutropin beta-subunit consists of 128 amino-acid residues, and exhibits 76-78% sequence identity with other avian lutropins beta, 44-50% with teleost gonadotropins II beta, 45% with amphibian lutropin beta, 41-44% with mammalian lutropins beta, and 25-36% with teleost gonadotropins I beta. Sequence comparison revealed that lutropin beta-subunits are more class-specific and have diversified approximately twice as fast follitropin beta-subunits, although segments essential for maintaining higher-order structures have been conserved.