A sperm motility-controlling protein adapted to the urodele mode of internal fertilization and its diversity among amphibian species

精子活力启动物质是一种非糖化蛋白，在尾纲两栖动物Cynops pyrrhogaster的内部受精模式中起特殊作用。在本研究中，鉴定了一个编码SMIS蛋白的cDNA。它编码了包含半胱氨酸结结构域的151个氨基酸序列。SMIS基因的表达是输卵管特异性的，不受排卵刺激的影响。利用具有SMIS部分氨基酸序列的合成肽，在半胱氨酸结结构域的亲水性环中检测到SMIS的活性位点。免疫印迹和southern印迹显示，与SMIS同源的蛋白在无尾猿和尾猿两栖动物中广泛保守，但同源蛋白的等电点在4 ~ 7之间存在差异。这些结果表明，SMIS的分子特征可能在适应两栖动物多样化受精方式的过程中发生了变化。

Sperm motility-initiating substance is a nonglycosilated protein that acts specifically in the mode of internal fertilization of the urodele amphibian, Cynops pyrrhogaster. In the present study, a cDNA encoding SMIS protein was identified. It coded a sequence of 151 amino acids that contained a cysteine knot domain. The expression of the SMIS gene was oviduct-specific and independent of the stimuli of ovulation. The active site of the SMIS was detected in a hydrophilic loop of the cysteine knot domain using synthetic peptides having partial amino acid sequences of the SMIS. Immunoblotting and southernblotting revealed that proteins homologous to SMIS were widely conserved among anuran and urodele amphibians but those homologues showed different isoelectric points ranging from 4 to 7. These results suggest that the molecular feature of the SMIS may be changed in adaptation to the diversified fertilization modes among amphibian species.