Abstract
Stromal interaction molecules (STIM)s function as endoplasmic reticulum calcium (Ca(2+)) sensors that differentially regulate plasma membrane Ca(2+) release activated Ca(2+) channels in various cells. To probe the structural basis for the functional differences between STIM1 and STIM2 we engineered a series of EF-hand and sterile α motif (SAM) domain (EF-SAM) chimeras, demonstrating that the STIM1 Ca(2+)-binding EF-hand and the STIM2 SAM domain are major contributors to the autoinhibition of oligomerization in each respective isoform. Our nuclear magnetic resonance (NMR) derived STIM2 EF-SAM structure provides a rationale for an augmented stability, which involves a 54° pivot in the EF-hand:SAM domain orientation permissible by an expanded nonpolar cleft, ionic interactions, and an enhanced hydrophobic SAM core, unique to STIM2. Live cells expressing "super-unstable" or "super-stable" STIM1/STIM2 EF-SAM chimeras in the full-length context show a remarkable correlation with the in vitro data. Together, our data suggest that divergent Ca(2+)- and SAM-dependent stabilization of the EF-SAM fold contributes to the disparate regulation of store-operated Ca(2+) entry by STIM1 and STIM2.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Binding Sites
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Calcium / metabolism*
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Calcium Channels / metabolism
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Cell Adhesion Molecules / chemistry
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Cell Adhesion Molecules / genetics
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Cell Adhesion Molecules / metabolism*
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EF Hand Motifs*
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Endoplasmic Reticulum / metabolism
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HEK293 Cells
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HeLa Cells
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Humans
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Hydrophobic and Hydrophilic Interactions
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Luminescent Proteins / genetics
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Luminescent Proteins / metabolism
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Magnetic Resonance Spectroscopy
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Membrane Potentials
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Membrane Proteins / chemistry
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Membrane Proteins / genetics
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Membrane Proteins / metabolism*
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Microscopy, Fluorescence
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Models, Molecular
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Molecular Sequence Data
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Neoplasm Proteins / chemistry
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism*
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ORAI1 Protein
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Protein Binding
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Protein Structure, Secondary
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Protein Structure, Tertiary
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Sequence Homology, Amino Acid
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Stromal Interaction Molecule 1
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Stromal Interaction Molecule 2
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Transfection
Substances
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Calcium Channels
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Cell Adhesion Molecules
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Luminescent Proteins
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Membrane Proteins
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Neoplasm Proteins
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ORAI1 Protein
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ORAI1 protein, human
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STIM1 protein, human
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STIM2 protein, human
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Stromal Interaction Molecule 1
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Stromal Interaction Molecule 2
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Calcium