MOLECULAR-CLONING IN THE MARMOSET SHOWS THAT SEMENOGELIN IS NOT THE PRECURSOR OF THE TRH-LIKE PEPTIDE PGLU-GLU-PRO AMIDE

Two peptides with similar structures to thyrotropin-releasing hormone (TRH), pGlu-Glu-Pro amide and pGlu-Phe-Pro amide, have been identified in human seminal fluid and it has been shown that one of these peptid es, pGlu-Glu-Pro amide, has the ability to increase the capacitation o f sperm cells, consistent with a role in fertility. In order to select a species in which there is a high degree of expression of the genes that code for 'TRH-like' peptides, we have determined the levels of th ese peptides in the prostate, pancreas and thyroid of a range of speci es including rat, rabbit, ox, marmoset, macaque and man. The peptides were extracted from the tissues and purified before determination by R IA with TRH antibody. In addition, trypsin digestion and TRH RIA was u sed to investigate the presence of N-extended forms. The highest conce ntrations of TRH-immunoreactive peptides were found in the tissues of the marmoset, Callithrix jacchus. Ion-exchange chromatography demonstr ated that marmoset thyroid contained principally authentic TRH, the pa ncreas contained both TRH and TRH-like peptides while the prostate con tained TRH-like peptides alone. Further purification by HPLC showed th at the main TRH-immunoreactive peptide in marmoset prostate was pGlu-G lu-Pro amide and a second component was identified as pGlu-Phe-Pro ami de. The results indicate that the biosynthesis of these peptides could be studied to advantage in the marmoset. The biosynthetic precursors of the TRH-like peptides have not been identified. To examine whether pGlu-Glu-Pro amide might originate from semenogelin, we determined the sequence of semenogelin in the marmoset. It exhibited a high degree o f homology with human semenogelin-I, but in place of the Lys-Gln-Glu-P ro sequence that might give rise to pGlu-Glu-Pro amide, marmoset semen ogelin possessed the sequence Ser-Gln-Asp-Gln which cannot serve as a precursor for a TRH-like peptide. Further evidence was obtained by Nor thern blot analysis of a range of marmoset tissues. The results showed that semenogelin is not present in marmoset prostate. It is concluded that pGlu-Glu-Pro amide originates from a precursor distinct from sem enogelin, both in marmoset and in man. (C) 1998 Elsevier Science B.V. All rights reserved.