Ishibashi K, Kuwahara M, Gu Y, Kageyama Y, Tohsaka A, Suzuki F, Marumo F, Sasaki S
Second Department of Internal Medicine, Tokyo Medical and Dental University, Tokyo 113, Japan.
J Biol Chem. 1997 Aug 15;272(33):20782-6. doi: 10.1074/jbc.272.33.20782.
A new member of the aquaporin (AQP) family has been identified from rat testis. This gene, referred as aquaporin 7 (AQP7), encodes a 269-amino acid protein that contained the conserved NPA motifs of MIP family proteins. AQP7 has the amino acid sequence homology with other aquaporins ( approximately 30%), and it is highest with AQP3 (48%), suggesting that both AQP3 and AQP7 belong to a subfamily in the MIP family. Injection of AQP7-cRNA into Xenopus oocytes expressed a 26-kDa protein detected by immunoblotting. The expression of AQP7 in oocytes stimulated the osmotic water permeability by 10-fold which was not inhibited by 0.3 mM mercury chloride. The Arrhenius activation energy for the stimulated water permeability was low (2.1 kcal/mol). AQP7 also facilitated glycerol and urea transport by 5- and 9-fold, respectively. The activation energy for glycerol was also low (5.3 kcal/mol after the correction of the endogenous glycerol permeability of oocytes). Northern blot analysis revealed a 1.5-kilobase pair transcript expressed abundantly in testis. In situ hybridization of testis revealed the expression of AQP7 at late spermatids in seminiferous tubules. The immunohistochemistry of testis localized the AQP7 expression at late spermatids and at maturing sperms. AQP7 may play an important role in sperm function.
水通道蛋白（AQP）家族的一个新成员已从大鼠睾丸中被鉴定出来。该基因被称为水通道蛋白7（AQP7），编码一种269个氨基酸的蛋白质，其包含MIP家族蛋白保守的NPA基序。AQP7与其他水通道蛋白具有氨基酸序列同源性（约30%），与AQP3的同源性最高（48%），这表明AQP3和AQP7都属于MIP家族中的一个亚家族。将AQP7 - cRNA注射到非洲爪蟾卵母细胞中，通过免疫印迹检测到表达了一种26 kDa的蛋白质。AQP7在卵母细胞中的表达使渗透水通透性提高了10倍，且不受0.3 mM氯化汞的抑制。刺激后的水通透性的阿伦尼乌斯活化能较低（2.1千卡/摩尔）。AQP7还分别使甘油和尿素的转运促进了5倍和9倍。甘油的活化能也较低（校正卵母细胞内源性甘油通透性后为5.3千卡/摩尔）。Northern印迹分析显示在睾丸中大量表达一种1.5千碱基对的转录本。睾丸的原位杂交显示在生精小管的晚期精子细胞中有AQP7的表达。睾丸的免疫组织化学将AQP7的表达定位在晚期精子细胞和成熟精子上。AQP7可能在精子功能中发挥重要作用。
