Mitani Namiki, Yamaji Naoki, Ma Jian Feng
Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki, Japan.
Pflugers Arch. 2008 Jul;456(4):679-86. doi: 10.1007/s00424-007-0408-y. Epub 2008 Jan 23.
Lsi1 (OsNIP2;1) is the first silicon (silicic acid) transporter identified in plant, which belongs to the nodulin 26-like intrinsic membrane protein (NIP) subfamily. In this study, we characterized the function of this transporter by using the Xenopus laevis oocyte expression system. The transport activity of Lsi1 for silicic acid was significantly inhibited by HgCl2 but not by low temperature. Lsi1 also showed an efflux transport activity for silicic acid. The substrate specificity study showed that Lsi1 was able to transport urea and boric acid; however, the transport activity for silicic acid was not affected by the presence of equimolar urea and was decreased only slightly by boric acid. Furthermore, among the NIPs subgroup, OsNIP2;2 showed transport activity for silicic acid, whereas OsNIP1;1 and OsNIP3;1 did not. We propose that Lsi1 and its close homologues form a unique subgroup of NIP with a distinct ar/R selectivity filter, which is located in the narrowest region on the extra-membrane mouth and govern the substrate specificity of the pore.
Lsi1（OsNIP2;1）是植物中鉴定出的首个硅（硅酸）转运蛋白，属于类结节蛋白26内在膜蛋白（NIP）亚家族。在本研究中，我们利用非洲爪蟾卵母细胞表达系统对该转运蛋白的功能进行了表征。Lsi1对硅酸的转运活性受到HgCl2的显著抑制，但不受低温影响。Lsi1对硅酸还表现出外向转运活性。底物特异性研究表明，Lsi1能够转运尿素和硼酸；然而，等摩尔尿素的存在并不影响其对硅酸的转运活性，硼酸仅使其转运活性略有降低。此外，在NIPs亚组中，OsNIP2;2表现出对硅酸的转运活性，而OsNIP1;1和OsNIP3;1则没有。我们提出，Lsi1及其紧密同源物形成了一个独特的NIP亚组，具有独特的ar/R选择性过滤器，位于膜外口最狭窄区域，决定了孔道的底物特异性。
