Uzdavinys Povilas, Coinçon Mathieu, Nji Emmanuel, Ndi Mama, Winkelmann Iven, von Ballmoos Christoph, Drew David
Centre for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
Department of Chemistry and Biochemistry, University of Bern, CH-3012 Bern, Switzerland
Proc Natl Acad Sci U S A. 2017 Feb 14;114(7):E1101-E1110. doi: 10.1073/pnas.1614521114. Epub 2017 Feb 1.
Sodium/proton exchangers of the family mediate the transport of protons in exchange for sodium to help regulate intracellular pH, sodium levels, and cell volume. In electrogenic Na/H antiporters, it has been assumed that two ion-binding aspartate residues transport the two protons that are later exchanged for one sodium ion. However, here we show that we can switch the antiport activity of the bacterial Na/H antiporter NapA from being electrogenic to electroneutral by the mutation of a single lysine residue (K305). Electroneutral lysine mutants show similar ion affinities when driven by [Formula: see text]pH, but no longer respond to either an electrochemical potential ([Formula: see text]) or could generate one when driven by ion gradients. We further show that the exchange activity of the human Na/H exchanger NHA2 () is electroneutral, despite harboring the two conserved aspartic acid residues found in NapA and other bacterial homologues. Consistently, the equivalent residue to K305 in human NHA2 has been replaced with arginine, which is a mutation that makes NapA electroneutral. We conclude that a transmembrane embedded lysine residue is essential for electrogenic transport in Na/H antiporters.
该家族的钠/质子交换器介导质子与钠的交换运输，以帮助调节细胞内pH值、钠水平和细胞体积。在生电钠/氢反向转运体中，人们认为两个离子结合天冬氨酸残基运输两个质子，随后这两个质子被一个钠离子交换。然而，我们在此表明，通过单个赖氨酸残基（K305）的突变，我们可以将细菌钠/氢反向转运体NapA的反向转运活性从生电转变为电中性。当由[公式：见正文]pH驱动时，电中性赖氨酸突变体显示出相似的离子亲和力，但不再对电化学势（[公式：见正文]）作出反应，也不能在由离子梯度驱动时产生电化学势。我们进一步表明，人类钠/氢交换器NHA2（）的交换活性是电中性的，尽管它含有在NapA和其他细菌同源物中发现的两个保守天冬氨酸残基。一致的是，人类NHA2中与K305等效的残基已被精氨酸取代，这种突变使NapA变为电中性。我们得出结论，跨膜嵌入的赖氨酸残基对于钠/氢反向转运体的生电运输至关重要。
