Structural and functional properties of two human FXYD3 (mat-8) isoforms
Structural and functional properties of two human FXYD3 (mat-8) isoforms
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DOI：
10.1074/jbc.m605221200
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发表时间：
2006-12-22
影响因子：
4.8
通讯作者：
Geering, Kaethi
中科院分区：
文献类型：
--
作者：
Bibert, Stephanie;Roy, Sophie;Geering, Kaethi
7种FXYD蛋白中的6种已被证明是Na，K-ATP酶的组织特异性调节剂。在这项研究中，我们在CaCo-2细胞中鉴定了人FXYD 3或Mat-8的两种剪接变体。短的人FXYD 3与小鼠FXYD 3具有72%的序列同一性，而长的人FXYD 3与短的人FXYD 3相同，但在跨膜结构域之后具有26个氨基酸的插入。短和长的人FXYD 3 RNA和蛋白质在CaCo-2细胞分化期间差异表达。长的人FXYD 3主要在未分化的细胞中表达，短的人FXYD 3主要在分化的细胞中表达，并且两种FXYD 3变体都可以与Na，K-ATP酶抗体共免疫沉淀。与小鼠FXYD 3（其具有两个跨膜结构域以缺乏信号肽的切割）相反，人FXYD 3具有可切割的信号肽并采用I型拓扑结构。在爪蟾卵母细胞中共表达后，两种人FXYD 3变体仅与Na，K-ATP酶同工酶稳定结合，而不与H，K-ATP酶或Ca-ATP酶稳定结合。与小鼠FXYD 3类似，短的人FXYD 3在大范围的膜电位上降低Na，K-ATP酶的表观K+和Na+亲和力。另一方面，长的人FXYD 3仅在轻微负和正膜电位下降低表观K+亲和力，并增加Na，K-ATP酶的表观Na+亲和力。最后，短和长的人FXYD 3都诱导超极化激活电流，类似于小鼠FXYD 3诱导的电流。因此，我们已经表征了在分化和未分化细胞中差异表达并显示不同功能特性的两种人FXYD 3同种型。
Six of 7 FXYD proteins have been shown to be tissue-specific modulators of Na, K-ATPase. In this study, we have identified two splice variants of human FXYD3, or Mat-8, in CaCo-2 cells. Short human FXYD3 has 72% sequence identity with mouse FXYD3, whereas long human FXYD3 is identical to short human FXYD3 but has a 26-amino acid insertion after the transmembrane domain. Short and long human FXYD3 RNAs and proteins are differentially expressed during differentiation of CaCo-2 cells. Long human FXYD3 is mainly expressed in non-differentiated cells and short human FXYD3 in differentiated cells and both FXYD3 variants can be co-immunoprecipitated with a Na, K-ATPase antibody. In contrast to mouse FXYD3, which has two transmembrane domains for lack of cleavage of the signal peptide, human FXYD3 has a cleavable signal peptide and adopts a type I topology. After co-expression in Xenopus oocytes, both human FXYD3 variants associate stably only with Na, K-ATPase isozymes but not with H, K-ATPase or Ca-ATPase. Similar to mouse FXYD3, short human FXYD3 decreases the apparent K+ and Na+ affinity of Na, K-ATPase over a large range of membrane potentials. On the other hand, long human FXYD3 decreases the apparent K+ affinity only at slightly negative and positive membrane potentials and increases the apparent Na+ affinity of Na, K-ATPase. Finally, both short and long human FXYD3 induce a hyperpolarization activated current, similar to that induced by mouse FXYD3. Thus, we have characterized two human FXYD3 isoforms that are differentially expressed in differentiated and non-differentiated cells and show different functional properties.