title: Phosphatidylinositol 4,5-bisphosphate increases Ca2+ affinity of synaptotagmin-1 by 40-fold.
abstract: Synaptotagmin-1 is the main Ca(2+) sensor of neuronal exocytosis. It binds to both Ca(2+) and the anionic phospholipid phosphatidylinositol 4,5-bisphosphate (PIP(2)), but the precise cooperativity of this binding is still poorly understood. Here, we used microscale thermophoresis to quantify the cooperative binding of PIP(2) and Ca(2+) to synaptotagmin-1. We found that PIP(2) bound to the well conserved polybasic patch of the C2B domain with an apparent dissociation constant of ∼20 μM. PIP(2) binding reduced the apparent dissociation constant for Ca(2+) from ∼250 to <5 μM. Thus, our data show that PIP(2) makes synaptotagmin-1 >40-fold more sensitive to Ca(2+). This interplay between Ca(2+), synaptotagmin-1, and PIP(2) is crucial for neurotransmitter release.
authors.affiliation: Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Georg-August University, 37077 Göttingen, Germany.
authors.forename: Geert
authors.initials: G
authors.lastname: van den Bogaart
authors.forename: Karsten
authors.initials: K
authors.lastname: Meyenberg
authors.forename: Ulf
authors.initials: U
authors.lastname: Diederichsen
authors.forename: Reinhard
authors.initials: R
authors.lastname: Jahn
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D050863:Synaptotagmin I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D018377:Neurotransmitter Agents; D019269:Phosphatidylinositol 4,5-Diphosphate; D050863:Synaptotagmin I; C494312:Syt1 protein, rat; D002118:Calcium