Sato Yoko, Sakaguchi Masao
Graduate School of Life Science, University of Hyogo, Ako, Hyogo 678-1297, Japan.
J Biochem. 2005 Oct;138(4):425-31. doi: 10.1093/jb/mvi132.
The membrane topology of the Arabidopsis thaliana Na(+)/H(+) exchanger isoform 1 (AtNHX1) was investigated by examining the topogenic function of transmembrane (TM) segments using a cell-free system. Even though the signal peptide found in the human Na(+)/H(+) exchanger (NHE) family is missing, the N-terminal hydrophobic segment was efficiently inserted into the membrane and had an N-terminus lumen topology depending on the next TM segment. The two N-terminal TM segments had the same topology as those of TM2 and TM3 of human NHE1. In contrast, TM2 and TM3 of human NHE1 did not acquire the correct topology when the signal peptide (denoted as TM1) was deleted. Furthermore, there were three hydrophobic segments with the same topogenic properties as the TM9-H10-TM10 segments of human NHE1, which has one lumenal loop (H10) and two flanking TM segments (TM9 and TM10). These data indicate that the plant NHX isoforms can form the common membrane topology proposed for the human NHE family, even though it does not have a signal peptide.
通过使用无细胞系统检测跨膜（TM）片段的拓扑形成功能，对拟南芥Na(+)/H(+)交换体亚型1（AtNHX1）的膜拓扑结构进行了研究。尽管在人类Na(+)/H(+)交换体（NHE）家族中发现的信号肽缺失，但N端疏水片段仍能有效插入膜中，且根据下一个TM片段，其N端具有腔拓扑结构。两个N端TM片段的拓扑结构与人类NHE1的TM2和TM3相同。相反，当信号肽（记为TM1）缺失时，人类NHE1的TM2和TM3无法获得正确的拓扑结构。此外，存在三个具有与人类NHE1的TM9-H10-TM10片段相同拓扑形成特性的疏水片段，人类NHE1有一个腔环（H10）和两个侧翼TM片段（TM9和TM10）。这些数据表明，植物NHX亚型可以形成人类NHE家族所提出的共同膜拓扑结构，尽管它没有信号肽。
