Data from: A new subfamily LIP of the major intrinsic proteins

Background: Proteins of the major intrinsic protein (MIP) family, or aquaporins, have been detected in almost all organisms. These proteins are important in cells and organisms because they allow for passive transmembrane transport of water and other small, uncharged polar molecules. Results: We compared the predicted amino acid sequences of 20 MIPs from several algae species of the phylum Heterokontophyta (Kingdom Chromista) with the sequences of MIPs from other organisms. Multiple sequence alignments revealed motifs that were homologous to functionally important NPA motifs and the so-called ar/R-selective filter of glyceroporins and aquaporins. The MIP sequences of the studied chromists fell into several clusters that belonged to different groups of MIPs from a wide variety of organisms from different Kingdoms. Two of these proteins belong to Plasma membrane intrinsic proteins (PIPs), four of them belong to GlpF-like intrinsic proteins (GIPs), and one of them belongs to a specific MIPE subfamily from green algae. Three proteins belong to the unclassified MIPs, two of which are of bacterial origin. Eight of the studied MIPs contain an NPM-motif in place of the second conserved NPA-motif typical of the majority of MIPs. The MIPs of heterokonts within all detected clusters can differ from other MIPs in the same cluster regarding the structure of the ar/R-selective filter and other generally conserved motifs. Conclusion: We proposed placing nine MIPs from heterokonts into a new group, which we have named the LIPs (large intrinsic proteins). The possible substrate specificities of the studied MIPs are discussed.研究背景：主要内在蛋白（major intrinsic protein, MIP）家族，亦称水通道蛋白（aquaporins），几乎在所有生物类群中均已被检出。这类蛋白在细胞及生物体内发挥关键功能，可介导水与其他小型不带电荷极性分子的被动跨膜转运。 研究结果：我们将色藻界（Chromista）不等鞭毛藻门（Heterokontophyta）多个藻类物种的20个MIP的预测氨基酸序列，与其他生物的MIP序列进行了比对。多序列比对结果显示，其中存在与功能重要的NPA基序以及甘油通道蛋白与水通道蛋白的所谓ar/R选择性过滤器同源的保守基序。本次研究的色藻界MIP序列可分为多个簇，分别隶属于不同生物界来源的各类MIP家族分支：其中2个蛋白属于质膜内在蛋白（Plasma membrane intrinsic proteins, PIPs），4个属于类GlpF内在蛋白（GlpF-like intrinsic proteins, GIPs），另有1个隶属于绿藻特有的MIPE亚家族；3个蛋白属于未分类MIP，其中2个源自细菌。本次研究的MIP中有8个携带NPM基序，替代了大多数MIP所共有的第二个保守NPA基序。所有检出簇中的不等鞭毛类MIP，在ar/R选择性过滤器与其他通用保守基序的结构上，均可能与同簇内其他MIP存在差异。 研究结论：我们提议将来自不等鞭毛类的9个MIP归入一个新的家族分支，将其命名为大内在蛋白（large intrinsic proteins, LIPs）。本文还对本次研究的MIP的潜在底物特异性进行了探讨。