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Nat Struct Mol Biol. 2016 Nov;23(11):965-973. doi: 10.1038/nsmb.3297. Epub 2016 Sep 26.

Skywalker-TBC1D24 has a lipid-binding pocket mutated in epilepsy and required for synaptic function.

Author information

1
Structural Biology Research Center, VIB, Brussels, Belgium.
2
Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium.
3
VIB Center for Brain &Disease Research, Leuven, Belgium.
4
KU Leuven, Department of Human Genetics, Leuven Institute for Neurodegenerative Disease (LIND), Leuven, Belgium.

Abstract

Mutations in TBC1D24 cause severe epilepsy and DOORS syndrome, but the molecular mechanisms underlying these pathologies are unresolved. We solved the crystal structure of the TBC domain of the Drosophila ortholog Skywalker, revealing an unanticipated cationic pocket conserved among TBC1D24 homologs. Cocrystallization and biochemistry showed that this pocket binds phosphoinositides phosphorylated at the 4 and 5 positions. The most prevalent patient mutations affect the phosphoinositide-binding pocket and inhibit lipid binding. Using in vivo photobleaching of Skywalker-GFP mutants, including pathogenic mutants, we showed that membrane binding via this pocket restricts Skywalker diffusion in presynaptic terminals. Additionally, the pathogenic mutations cause severe neurological defects in flies, including impaired synaptic-vesicle trafficking and seizures, and these defects are reversed by genetically increasing synaptic PI(4,5)P2 concentrations through synaptojanin mutations. Hence, we discovered that a TBC domain affected by clinical mutations directly binds phosphoinositides through a cationic pocket and that phosphoinositide binding is critical for presynaptic function.

PMID:
27669036
DOI:
10.1038/nsmb.3297
[Indexed for MEDLINE]
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