The down regulated in adenoma (dra) gene product binds to the second PDZ domain of the NHE3 kinase a regulatory protein (E3KARP), potentially linking intestinal Cl-/HCO3- exchange to Na+/H+ exchange
The down regulated in adenoma (dra) gene product binds to the second PDZ domain of the NHE3 kinase a regulatory protein (E3KARP), potentially linking intestinal Cl-/HCO3- exchange to Na+/H+ exchange
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DOI：
10.1021/bi0259103
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发表时间：
2002-10-15
期刊：
影响因子：
2.9
通讯作者：
Seidler, U
中科院分区：
文献类型：
--
作者：
Lamprecht, G;Heil, A;Seidler, U
肠道电中性NaCl吸收是由肠上皮细胞顶膜上的Na⁺/H⁺和Cl⁻/HCO₃⁻交换的并行作用所介导。所涉及的离子转运体是Na⁺/H⁺交换体3（NHE3）以及腺瘤下调（dra）基因产物。环腺苷酸（cAMP）介导的对NHE3的抑制作用需要转运体与衔接蛋白NHE3激酶A调节蛋白（E3KARP）的第二个PDZ（PSD95、Dlg、ZO1）结构域结合。由于dra的C末端四个氨基酸是ETKF（谷氨酸 - 苏氨酸 - 赖氨酸 - 苯丙氨酸），类似于一个PDZ相互作用基序，我们假设dra也可能与E3KARP的一个PDZ结构域结合。在体外，dra的ETKF基序与E3KARP的第二个PDZ结构域结合，其亲和力与已知配体囊性纤维化跨膜传导调节因子（CFTR）相当。C末端的苯丙氨酸是PDZ相互作用基序中的一个非常规残基，只能被经典残基亮氨酸替代，而不能被其他疏水残基（缬氨酸、异亮氨酸）替代。免疫荧光显示dra、NHE3和E3KARP在人近端结肠的顶侧区域共定位。我们提出一个模型，其中NHE3和dra都与E3KARP的第二个PDZ结构域结合，并且转运体的连接是通过E3KARP的二聚化发生的。在这样一个模型中，第一个PDZ结构域将可用于例如信号转导蛋白。
Intestinal electroneutral NaCl absorption is mediated by parallel operation of Na+/H+ and Cl-/HCO3- exchange in the enterocyte apical membrane. The ion transporters involved are Na+/H+ exchanger 3 (NHE3) and the down regulated in adenoma (dra) gene product. cAMP-mediated inhibition of NHE3 requires the transporter to bind to the second PDZ (PSD95, disk large, ZO1) domain of the adapter protein NHE3 kinase A regulatory protein (E3KARP). Because the C-terminal four amino acids of dra are ETKF (glutamate-threonine-lysine-phenylalanine), resembling a PDZ interaction motif, we hypothesized that dra may also bind to one of the PDZ domains of E3KARP. In vitro the ETKF motif of dra binds to the second PDZ domain of E3KARP, the affinity being comparable to that of the known ligand CFTR. The C-terminal phenylalanine, which is an unconventional residue in PDZ interaction motifs, can only be substituted by the classical residue leucine, but not by other hydrophobic residues (valine, isoleucine). Immunofluorescence colocalizes dra, NHE3, and E3KARP in the apical compartment of human proximal colon. We suggest a model in which both NHE3 and dra bind to the second PDZ domain of E3KARP and that linking of the transporters occurs through dimerization of E3KARP. In such a model, the first PDZ domain would remain available for instance for signal transduction proteins.