Evidence that a calmodulin-like calcium-binding domain of the FSH beta-subunit is involved in FSH-induced calcium uptake by Sertoli cells.

ABSTRACT

We have previously shown that a synthetic peptide amide corresponding to residues 1-15 of the human FSH beta-subunit (hFSH-beta-(1-15)) possesses structural characteristics and calcium-binding properties similar to the calcium-binding loops of calmodulin (CaM). The calcium-binding property of hFSH-beta-(1-15) correlated well with its ability to stimulate uptake of calcium (as 45Ca2+) by cultured rat Sertoli cells and proteoliposomes enriched with bovine calf testis FSH receptors. A sequence found in the calcium-binding loops of CaM and a number of other calcium-binding proteins can be represented by the motif +-+-+-+-+--+, where + represents a calcium-binding residue and - represents a non-binding residue. A sequence containing a similar motif appears in hFSH-beta-(1-15) between residues 4 and 15 +-++-+---+-+. Using a synthetic peptide strategy, we undertook to determine whether the first three residues of hFSH-beta-(1-15) were required to induce uptake of calcium by cultured rat Sertoli cells and FSH receptor-enriched proteoliposomes, and to assess whether rearrangement of the putative calcium-binding ligands (+) of hFSH-beta-(1-15) to correspond to their linear sequence in CaM would enhance the ability of hFSH-beta-(1-15) to induce calcium uptake in these two model systems.(ABSTRACT TRUNCATED AT 250 WORDS)