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Synthetic human follicle-stimulating hormone-beta-(1-15) peptide-amide binds Ca2+ and possesses sequence similarity to calcium binding sites of calmodulin.

To determine the basis for the previously demonstrated calcium requirement for specific binding of FSH to receptor, 11 overlapping peptide amides representing the entire primary structure of human FSH (hFSH)-beta-subunit were tested for their ability to bind 45Ca2+ as an approach to identifying possible calcium binding regions of the hormone. hFSH-beta-(1-15)-peptide amide bound significant amounts of 45Ca2+. This peptide contains an amino acid sequence similar to that found in the loop structures of the calcium-binding domains of calmodulin. The affinity of hFSH-beta-(1-15)-peptide amide for calcium (Kd = 1.2 +/- 0.3 mM) was similar to that previously reported for a synthetic peptide corresponding to calmodulin binding site III. No such sequence is predicted in the recently deduced primary structure of the FSH receptor. FSH-beta-(1-15) may, therefore, be associated with the calcium requirement for specific binding of FSH to receptor. The calcium binding property of this calmodulin-like peptide also correlates well with its ability to induce uptake of calcium into liposomes via transmembrane channel formation, as previously reported by this laboratory.