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 α-subunit and a hormone-specific β-subunit. The α-subunit is composed of 96 amino acid residues and has 70–80% sequence identity with the α-subunits of most vertebrates. The ostrich follitropin β-subunit consists of 106 amino-acid residues, and shows 70–74% sequence identity with mammalian follitropins β, 61% with amphibian follitropin β, 39–46% with teleost gonadotropins IIβ and 32–44% with teleost gonadotropins Iβ. The ostrich lutropin β-subunit consists of 128 amino-acid residues, and exhibits 76–78% sequence identity with other avian lutropins β, 44–50% with teleost gonadotropins IIβ, 45% with amphibian lutropin β, 41–44% with mammalian lutropins β, and 25–36% with teleost gonadotropins Iβ. Sequence comparison revealed that lutropin β-subunits are more class-specific and have diversified approximately twice as fast follitropin β-subunits, although segments essential for maintaining higher-order structures have been conserved.