A synthetic peptide representing residues 7 to 21 of human luteinizing hormone beta-subunit binds calcium, facilitates calcium uptake by liposomes and possesses sequence similarity to calcium-binding domains of calmodulin.
We have previously demonstrated that a synthetic peptide corresponding to residues 1 to 15 of hFSH-beta-subunit (hFSH-beta-(1-15)) shares sequence homology with the calcium-binding domains of calmodulin (CaM), binds calcium with an affinity similar to that of CaM-binding loop III (CaM III) and facilitates uptake of external calcium by liposomes and cultured rat Sertoli cells. We noted a sequence homologous to hFSH-beta-(1-15) between residues 7 to 21 of the beta-subunits of both hLH and hCG. A peptide amide representing this region of hLH-beta (hLH-beta-(7-21)) and an N-terminal truncated analog (hLH-beta-(10-21)) that more closely resembles the calcium-binding loops of calmodulin were synthesized and tested for their ability to bind 45Ca2+, and facilitate uptake of 45Ca2+ by liposomes. hLH-beta-(7-21) and hLH-beta-(10-21) bound significant amounts of 45Ca2+ with affinities of 1.2 +/- 0.4 and 0.7 +/- 0.3 mM, respectively, values virtually identical to that reported for a synthetic peptide corresponding to CaM III. The two peptides also facilitated specific, concentration-related and saturable uptake of 45Ca2+ by liposomes, which was sensitive to blockade by voltage-independent calcium-channel antagonists. Our data suggest that residues 7 to 21 of the beta-subunit of hLH may be associated with the previously demonstrated calcium requirement for specific binding of LH to its receptor, and that the calcium-binding property of this region is related to its ability to facilitate uptake of calcium into liposomes via the formation of calcium-conducting transmembrane channels.
Grasso
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Department of Biochemistry and Molecular Biology, Albany Medical College A-10, NY 12208, USA.
D000818:Animals; D001665:Binding Sites; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D007986:Luteinizing Hormone / Q000737:chemistry* / Q000378:metabolism; D009543:Nifedipine / Q000494:pharmacology; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology
D002147:Calmodulin; D008081:Liposomes; D010446:Peptide Fragments; D012430:Ruthenium Red; D007986:Luteinizing Hormone; D009543:Nifedipine; D002118:Calcium