The rainbow trout CMP-sialic acid synthetase utilises a nuclear localization signal different from that identified in the mouse enzyme.
The rainbow trout CMP-sialic acid synthetase utilises a nuclear localization signal different from that identified in the mouse enzyme.
复制标题
DOI：
10.1093/glycob/cwm064
复制
发表时间：
2007-09
期刊：
影响因子：
4.3
通讯作者：
J. Tiralongo;A. Fujita;C. Sato;K. Kitajima;F. Lehmann;M. Oschlies;R. Gerardy-Schahn;Anja K Münster-Kühnel
中科院分区：
文献类型：
--
作者：
J. Tiralongo;A. Fujita;C. Sato;K. Kitajima;F. Lehmann;M. Oschlies;R. Gerardy-Schahn;Anja K Münster-Kühnel
末端糖唾液酸（Sia）在细胞-细胞相互作用和识别中起着关键作用。生物合成唾液酸糖缀合物的先决条件是通过CMP-Sia合成酶（CMP-Sia-syn）将Sia活化为胞苷一磷酸-Sia（CMP-Sia）。CMP-Sia-syn从细菌到人都是保守的，并且已经发现存在于迄今为止分析的所有脊椎动物物种的细胞核中。我们以前从虹鳟鱼（rt）中克隆了CMP-Sia-syn，并鉴定了三个可能作为核定位信号（NLS）的碱性氨基酸簇（BC）。在这里，我们利用嵌合蛋白和rt CMP-Sia-syn突变体，其中假定的NLS序列被删除，以确定核转运信号。与小鼠酶不同，在小鼠酶中，关键的NLS是酶活性位点的一部分，在rt CMP-Sia-syn中，NLS和活性位点是不同的。鱼酶中关键的NLS是二分的，功能取决于游离的N-末端。在小鼠和鱼细胞中的所有推定的rt NLS的比较分析确定了第二个劣基序（rtBC 5 -6），这是功能性的，仅在鱼细胞中，这表明在运输机制或折叠变异性在鱼中的一些差异。此外，基于对来自远距离后口动物的推定CMP-Sia-syn的计算分析，得出结论，CMP-Sia-syn核定位是相对较新的发明，起源于棘皮动物。总之，我们的数据描述了脊椎动物CMP-Sia-syn的NLS的结构差异，以及Sia激活与酶的亚细胞定位的独立性，提供了支持核定位与第二个未知功能相关的证据。
The terminal sugar sialic acid (Sia) plays a pivotal role in cell-cell interaction and recognition. A prerequisite for the biosynthesis of sialoglycoconjugates is the activation of Sia to cytidine monophosphate-Sia (CMP-Sia), by CMP-Sia synthetases (CMP-Sia-syn). CMP-Sia-syn are conserved from bacteria to man, and have been found to reside in the nucleus of all vertebrate species analysed to date. We previously cloned the CMP-Sia-syn from rainbow trout (rt) and identified three clusters of basic amino acids (BC) that might act as nuclear localization signals (NLS). Here, we utilised chimeric proteins and rt CMP-Sia-syn mutants in which putative NLS sequences were deleted, to identify the nuclear transport signal. Divergent from the mouse enzyme, where the crucial NLS is part of the enzyme's active site, in the rt CMP-Sia-syn the NLS and active site are disparate. The crucial NLS in the fish enzyme is bipartite and the functionality depends on a free N-terminus. Comparative analysis of all putative rt NLS in mouse and fish cells identified a second inferior motif (rtBC5-6), which was functional only in fish cells suggesting some differences in transport mechanism or folding variabilities in fish. Moreover, based on computational analyses of putative CMP-Sia-syn from distant deuterostomian organisms it was concluded that CMP-Sia-syn nuclear localization is a relatively recent invention, originating in echinoderms. In summary, our data describing structural differences in the NLS of vertebrate CMP-Sia-syn, and the independence of Sia activation from the subcellular localization of the enzyme, provide supporting evidence that nuclear localization is linked to a second yet unknown function.