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Article

  • The EMBO Journal (2006) 25, 2315 - 2325
  • doi:10.1038/sj.emboj.7601145

Published online: 18 May 2006

Crystal structure of CHP2 complexed with NHE1-cytosolic region and an implication for pH regulation

Youssef Ben Ammar1,a, Soichi Takeda2,3,a, Takashi Hisamitsu1, Hidezo Mori2 and Shigeo Wakabayashi1

  1. Department of Molecular Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
  2. Department of Cardiac Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
  3. Laboratory of Structural Biochemistry, RIKEN Harima Institute at SPring-8, Kouto, Mikazuki-cho, Sayo, Hyogo, Japan

Correspondence to:

Shigeo Wakabayashi, Department of Molecular Physiology, National Cardiovascular Center Research Institute, Fujishirodai 5-7-1, Suita, Osaka 565-8565, Japan. Tel.: +81 6 6833 5012; Fax: +81 6 6835 5314; E-mail: wak@ri.ncvc.go.jp

aThese authors contributed equally to this work

Received 5 December 2005; Accepted 24 April 2006

The plasma membrane Na+/H+ exchangers (NHE) require calcineurin B homologous protein (CHP) as an obligatory binding partner for ion transport. Here, we report the first crystal structure of CHP (CHP2 isoform) in complex with its binding domain in NHE1. We show that the cytoplasmic alpha-helix of NHE1 is inserted into the hydrophobic cleft formed by N- and C-lobes of CHP2 and that the size and shape of this crevice together with hydrogen bond formation at multiple positions assure a high degree of specificity for interaction with NHE members. Structure-based mutagenesis revealed the importance of hydrophobic interactions between CHP/NHE1 for the function of NHE1. Furthermore, the crystal structure shows the existence of a protruding CHP-unique region, and deletion of this region in CHP2 inhibited the NHE1 activity by inducing the acidic shift of intracellular pH dependence, while preserving interaction with NHE1. These findings suggest that CHP serves as an obligatory subunit that is required both for supporting the basic activity and regulating the pH-sensing of NHE1 via interactions between distinct parts of these proteins.

  • Keywords:

    • calcineurin homologous protein,
    • crystal structure,
    • Na+/H+ exchanger,
    • pH regulation