title: Structure and Ca²⁺-binding properties of the tandem C₂ domains of E-Syt2.
abstract: Contacts between the endoplasmic reticulum and the plasma membrane involve extended synaptotagmins (E-Syts) in mammals or tricalbins in yeast, proteins with multiple C₂ domains. One of the tandem C₂ domains of E-Syt2 is predicted to bind Ca²⁺, but no Ca²⁺-dependent function has been attributed to this protein. We have determined the crystal structures of the tandem C₂ domains of E-Syt2 in the absence and presence of Ca²⁺ and analyzed their Ca²⁺-binding properties by nuclear magnetic resonance spectroscopy. Our data reveal an unexpected V-shaped structure with a rigid orientation between the two C₂ domains that is not substantially altered by Ca²⁺. The E-Syt2 C2A domain binds up to four Ca²⁺ ions, whereas the C₂B domain does not bind Ca²⁺. These results suggest that E-Syt2 performs an as yet unidentified Ca²⁺-dependent function through its C₂A domain and uncover fundamental differences between the properties of the tandem C₂ domains of E-Syts and synaptotagmins.
authors.affiliation: Department of Biophysics, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Junjie
authors.initials: J
authors.lastname: Xu
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University Medical School, 265 Campus Drive, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University Medical School, 265 Campus Drive, Stanford, CA 94305, USA.
authors.forename: Taulant
authors.initials: T
authors.lastname: Bacaj
authors.affiliation: Department of Biophysics, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Zhou
authors.affiliation: Department of Biophysics, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA.
authors.forename: Diana R
authors.initials: DR
authors.lastname: Tomchick
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University Medical School, 265 Campus Drive, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University Medical School, 265 Campus Drive, Stanford, CA 94305, USA.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Südhof
authors.affiliation: Department of Biophysics, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA; Department of Pharmacology, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390, USA. Electronic address: jose@arnie.swmed.edu.
authors.forename: Josep
authors.initials: J
authors.lastname: Rizo
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D002942:Circular Dichroism; D018076:DNA, Complementary / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D007477:Ions; D009682:Magnetic Resonance Spectroscopy; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D050857:Synaptotagmins / Q000737:chemistry*; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D018076:DNA, Complementary; C573315:ESYT2 protein, human; D007477:Ions; D050857:Synaptotagmins; D002118:Calcium