Membrane Docking of the Synaptotagmin 7 C2A Domain: Electron Paramagnetic Resonance Measurements Show Contributions from Two Membrane Binding Loops.

摘要: The synaptotagmin (Syt) family of proteins plays an important role in vesicle docking and fusion during Ca(2+)-induced exocytosis a wide variety cell types. Its as Ca(2+) sensor derives primarily from its two C2 domains, C2A C2B, which insert into anionic lipid membranes upon binding Ca(2+). Syt isoforms 1 7 differ significantly their sensitivity; the domain Syt7 binds much more tightly than Syt1, at least part because greater contributions hydrophobic effect. While structure membrane activity Syt1 have been extensively studied, structural origins differences between are unknown. This study used site-directed spin labeling electron paramagnetic resonance spectroscopy to determine depth parameters for domain, comparison analogous previous measurements with domain. In novel approach, geometry both was modeled by mapping onto multiple molecular dynamics-simulated structures Ca(2+)-bound protein. models reveal penetration loops (CBL1) 3 (CBL3), is sensitive mutations CBL3. On average, inserts deeply C2A, although depths vary among different models. observation provides partial explanation hydrophobically driven C2A.