Huber A E, Fraser H, del Rio-Garcia J, Kreil G, Smyth D G
Institute of Molecular Biology, Billrothstrasse 11, A-5020 Salzburg, Austria.
Biochim Biophys Acta. 1998 Sep 8;1387(1-2):143-52. doi: 10.1016/s0167-4838(98)00116-2.
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 peptides, pGlu-Glu-Pro amide, has the ability to increase the capacitation of 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 these peptides in the prostate, pancreas and thyroid of a range of species including rat, rabbit, ox, marmoset, macaque and man. The peptides were extracted from the tissues and purified before determination by RIA with TRH antibody. In addition, trypsin digestion and TRH RIA was used to investigate the presence of N-extended forms. The highest concentrations of TRH-immunoreactive peptides were found in the tissues of the marmoset, Callithrix jacchus. Ion-exchange chromatography demonstrated that marmoset thyroid contained principally authentic TRH, the pancreas contained both TRH and TRH-like peptides while the prostate contained TRH-like peptides alone. Further purification by HPLC showed that the main TRH-immunoreactive peptide in marmoset prostate was pGlu-Glu-Pro amide and a second component was identified as pGlu-Phe-Pro amide. 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 of homology with human semenogelin-I, but in place of the Lys-Gln-Glu-Pro sequence that might give rise to pGlu-Glu-Pro amide, marmoset semenogelin possessed the sequence Ser-Gln-Asp-Gln which cannot serve as a precursor for a TRH-like peptide. Further evidence was obtained by Northern 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 semenogelin, both in marmoset and in man.
在人类精液中已鉴定出两种结构与促甲状腺激素释放激素（TRH）相似的肽，即焦谷氨酸 - 谷氨酸 - 脯氨酰胺和焦谷氨酸 - 苯丙氨酸 - 脯氨酰胺，并且已表明其中一种肽，焦谷氨酸 - 谷氨酸 - 脯氨酰胺，具有增加精子细胞获能的能力，这与它在生育中的作用相符。为了选择一种“TRH样”肽编码基因高度表达的物种，我们测定了包括大鼠、兔子、牛、狨猴、猕猴和人类在内的一系列物种的前列腺、胰腺和甲状腺中这些肽的水平。肽从组织中提取并纯化，然后用TRH抗体通过放射免疫分析（RIA）进行测定。此外，用胰蛋白酶消化和TRH RIA来研究N端延伸形式的存在。在狨猴（Callithrix jacchus）的组织中发现了最高浓度的TRH免疫反应性肽。离子交换色谱表明，狨猴甲状腺主要含有天然TRH，胰腺含有TRH和TRH样肽，而前列腺仅含有TRH样肽。通过高效液相色谱（HPLC）进一步纯化表明，狨猴前列腺中主要的TRH免疫反应性肽是焦谷氨酸 - 谷氨酸 - 脯氨酰胺，第二种成分被鉴定为焦谷氨酸 - 苯丙氨酸 - 脯氨酰胺。结果表明，在狨猴中研究这些肽的生物合成可能具有优势。尚未鉴定出TRH样肽的生物合成前体。为了研究焦谷氨酸 - 谷氨酸 - 脯氨酰胺是否可能源自精液凝胶蛋白，我们测定了狨猴精液凝胶蛋白的序列。它与人类精液凝胶蛋白 - I具有高度同源性，但狨猴精液凝胶蛋白没有可能产生焦谷氨酸 - 谷氨酸 - 脯氨酰胺的赖氨酸 - 谷氨酰胺 - 谷氨酸 - 脯氨酸序列，而是具有丝氨酸 - 谷氨酰胺 - 天冬酰胺 - 谷氨酰胺序列，该序列不能作为TRH样肽的前体。通过对一系列狨猴组织的Northern印迹分析获得了进一步的证据。结果表明，狨猴前列腺中不存在精液凝胶蛋白。得出的结论是，在狨猴和人类中，焦谷氨酸 - 谷氨酸 - 脯氨酰胺均源自与精液凝胶蛋白不同的前体。
