Kuwahara M, Ishibashi K, Gu Y, Terada Y, Kohara Y, Marumo F, Sasaki S
Second Department of Internal Medicine, School of Medicine, Tokyo Medical and Dental University, Tokyo 113-8519, Japan.
Am J Physiol. 1998 Dec;275(6):C1459-64. doi: 10.1152/ajpcell.1998.275.6.C1459.
A genome project focusing on the nematode Caenorhabditis elegans has demonstrated the presence of eight cDNAs belonging to the major intrinsic protein superfamily. We functionally characterized one of these cDNAs named C01G6.1. Injection of C01G6.1 cRNA increased the osmotic water permeability (Pf) of Xenopus oocytes 11-fold and the urea permeability 4.5-fold but failed to increase the glycerol permeability. It has been speculated that the MIP family may be separated into two large subfamilies based on the presence or absence of two segments of extra amino acid residues ( approximately 15 amino acids) at the second and third extracellular loops. Because C01G6.1 (designated AQP-CE1), AQP3, and glycerol facilitator (GlpF) all have these two segments, we replaced the segments of AQP-CE1 with those of AQP3 and GlpF to identify their roles. The functional characteristics of these mutants were principally similar to that of wild-type AQP-CE1, although the values of Pf and urea permeability were decreased by 39-74% and 28-65%, respectively. These results suggest that the two segments of extra amino acid residues may not contribute to channel selectivity or formation of the route for small solutes.
一个聚焦于秀丽隐杆线虫的基因组计划已证明存在八个属于主要内在蛋白超家族的cDNA。我们对其中一个名为C01G6.1的cDNA进行了功能表征。注射C01G6.1的cRNA使非洲爪蟾卵母细胞的渗透水通透性（Pf）增加了11倍，尿素通透性增加了4.5倍，但未能增加甘油通透性。据推测，基于在第二和第三细胞外环处是否存在两段额外的氨基酸残基（约15个氨基酸），MIP家族可能被分为两个大的亚家族。由于C01G6.1（命名为AQP-CE1）、AQP3和甘油转运体（GlpF）都有这两段氨基酸残基，我们将AQP-CE1的这两段氨基酸残基替换为AQP3和GlpF的相应残基，以确定它们的作用。这些突变体的功能特性与野生型AQP-CE1基本相似，尽管Pf和尿素通透性的值分别降低了39 - 74%和28 - 65%。这些结果表明，这两段额外的氨基酸残基可能对通道选择性或小溶质途径的形成没有贡献。
