Ca2+ regulation in the Na+/Ca2+ exchanger features a dual electrostatic switch mechanism.

Regulation of ion-transport in the Na(+)/Ca(2+) exchanger (NCX) occurs via its cytoplasmic Ca(2+)-binding domains, CBD1 and CBD2. Here, we present a mechanism for NCX activation and inactivation based on data obtained using NMR, isothermal titration calorimetry (ITC) and small-angle X-ray scattering (SAXS). We initially determined the structure of the Ca(2+)-free form of CBD2-AD and the structure of CBD2-BD that represent the two major splice variant classes in NCX1.

Structural basis for Ca2+ regulation in the Na+/Ca2+ exchanger.

Binding of Na+ and Ca2+ ions to the large cytosolic loop of the Na+/Ca2+ exchanger (NCX) regulates its ion transport across the plasma membrane. We determined the solution structures of two Ca2+-binding domains (CBD1 and CBD2) that, together with an alpha-catenin-like domain (CLD) form the regulatory exchanger loop. CBD1 and CBD2 constitute a novel Ca2+-binding motif and are very similar in the Ca2+-bound state.

Ca2+ regulation in the Na+/Ca2+ exchanger involves two markedly different Ca2+ sensors.

The plasma membrane Na+/Ca2+ exchanger (NCX) is almost certainly the major Ca2+ extrusion mechanism in cardiac myocytes. Binding of Na+ and Ca2+ ions to its large cytosolic loop regulates ion transport of the exchanger. We determined the solution structures of two Ca2+ binding domains (CBD1 and CBD2) that, together with an alpha-catenin-like domain (CLD), form the regulatory exchanger loop.

Role of structural and dynamical plasticity in Sin3: the free PAH2 domain is a folded module in mSin3B.

The co-repressor Sin3 is the essential scaffold protein of the Sin3/HDAC co-repressor complex, which is recruited to the DNA by a diverse group of transcriptional repressors, targeting genes involved in the regulation of the cell cycle, proliferation and differentiation. Sin3 contains four repeats commonly denoted as paired amphipathic helix (PAH1-4) domains that provide the principal interaction surface for various repressors. Here, we present the first structure of the free state of the PAH2 domain and discuss its implications for interaction with the repressors.

Kinetic folding mechanism of PDZ2 from PTP-BL.

PDZ domains represent a large family of protein-interaction modules associated with a variety of unrelated proteins with different functions. We report a complete characterization of the kinetic folding mechanism of a fluorescent variant of PDZ2 from PTP-BL, investigated under a variety of different experimental conditions. For this purpose, we engineered a fluorescent variant of this protein Y43W (called pseudo-wild-type, pWT43).