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 C 2 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.
|Original language||English (US)|
|Number of pages||12|
|State||Published - Feb 4 2014|
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology