Department of Cell and Tissue Biology, University of California San Francisco, San Francisco, CA, USA.
Biochem J. 2012 Sep 15;446(3):427-35. doi: 10.1042/BJ20120535.
NHE1 (Na(+)/H(+) exchanger isoform 1) has been reported to be hyperactive in 4.1R-null erythrocytes [Rivera, De Franceschi, Peters, Gascard, Mohandas and Brugnara (2006) Am. J. Physiol. Cell Physiol. 291, C880-C886], supporting a functional interaction between NHE1 and 4.1R. In the present paper we demonstrate that 4.1R binds directly to the NHE1cd (cytoplasmic domain of NHE1) through the interaction of an EED motif in the 4.1R FERM (4.1/ezrin/radixin/moesin) domain with two clusters of basic amino acids in the NHE1cd, K(519)R and R(556)FNKKYVKK, previously shown to mediate PIP(2) (phosphatidylinositol 4,5-bisphosphate) binding [Aharonovitz, Zaun, Balla, York, Orlowski and Grinstein (2000) J. Cell. Biol. 150, 213-224]. The affinity of this interaction (K(d) = 100-200 nM) is reduced in hypertonic and acidic conditions, demonstrating that this interaction is of an electrostatic nature. The binding affinity is also reduced upon binding of Ca(2+)/CaM (Ca(2+)-saturated calmodulin) to the 4.1R FERM domain. We propose that 4.1R regulates NHE1 activity through a direct protein-protein interaction that can be modulated by intracellular pH and Na(+) and Ca(2+) concentrations.
NHE1（Na(+)/H(+) 交换体同工型 1）在 4.1R 缺失的红细胞中被报道过度活跃[Rivera、De Franceschi、Peters、Gascard、Mohandas 和 Brugnara（2006）Am. J. Physiol. Cell Physiol. 291，C880-C886]，支持 NHE1 和 4.1R 之间的功能相互作用。在本文中，我们证明 4.1R 通过 4.1R FERM（4.1/ezrin/radixin/moesin）结构域中的 EED 基序与 NHE1cd 中的两个碱性氨基酸簇 K(519)R 和 R(556)FNKKYVKK 相互作用，直接与 NHE1cd 结合，先前已证明该相互作用介导 PIP(2)（磷脂酰肌醇 4,5-二磷酸）结合[Aharonovitz、Zaun、Balla、York、Orlowski 和 Grinstein（2000）J. Cell. Biol. 150，213-224]。这种相互作用的亲和力（K(d) = 100-200 nM）在高渗和酸性条件下降低，表明这种相互作用具有静电性质。当 Ca(2+)/CaM（Ca(2+)-饱和钙调蛋白）结合到 4.1R FERM 结构域时，结合亲和力也降低。我们提出，4.1R 通过一种直接的蛋白质-蛋白质相互作用来调节 NHE1 活性，这种相互作用可以通过细胞内 pH 值以及 Na(+)和 Ca(2+)浓度来调节。
