title: Structure of human Na+/H+ exchanger NHE1 regulatory region in complex with calmodulin and Ca2+.
abstract: The ubiquitous mammalian Na(+)/H(+) exchanger NHE1 has critical functions in regulating intracellular pH, salt concentration, and cellular volume. The regulatory C-terminal domain of NHE1 is linked to the ion-translocating N-terminal membrane domain and acts as a scaffold for signaling complexes. A major interaction partner is calmodulin (CaM), which binds to two neighboring regions of NHE1 in a strongly Ca(2+)-dependent manner. Upon CaM binding, NHE1 is activated by a shift in sensitivity toward alkaline intracellular pH. Here we report the 2.23 Å crystal structure of the NHE1 CaM binding region (NHE1(CaMBR)) in complex with CaM and Ca(2+). The C- and N-lobes of CaM bind the first and second helix of NHE1(CaMBR), respectively. Both the NHE1 helices and the Ca(2+)-bound CaM are elongated, as confirmed by small angle x-ray scattering analysis. Our x-ray structure sheds new light on the molecular mechanisms of the phosphorylation-dependent regulation of NHE1 and enables us to propose a model of how Ca(2+) regulates NHE1 activity.
authors.affiliation: Department of Structural Biology, Max Planck Institute of Biophysics, Max-von-Laue Str. 3, 60438 Frankfurt am Main, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Köster
authors.forename: Tea
authors.initials: T
authors.lastname: Pavkov-Keller
authors.forename: Werner
authors.initials: W
authors.lastname: Kühlbrandt
authors.forename: Özkan
authors.initials: Ö
authors.lastname: Yildiz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D002460:Cell Line; D018360:Crystallography, X-Ray; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D051381:Rats; D053838:Scattering, Small Angle; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D027682:Cation Transport Proteins; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D002118:Calcium