Munc13 C2B domain is an activity-dependent Ca2+ regulator of synaptic exocytosis.
Munc13 is a multidomain protein present in presynaptic active zones that mediates the priming and plasticity of synaptic vesicle exocytosis, but the mechanisms involved remain unclear. Here we use biophysical, biochemical and electrophysiological approaches to show that the central C(2)B domain of Munc13 functions as a Ca(2+) regulator of short-term synaptic plasticity. The crystal structure of the C(2)B domain revealed an unusual Ca(2+)-binding site with an amphipathic alpha-helix. This configuration confers onto the C(2)B domain unique Ca(2+)-dependent phospholipid-binding properties that favor phosphatidylinositolphosphates. A mutation that inactivated Ca(2+)-dependent phospholipid binding to the C(2)B domain did not alter neurotransmitter release evoked by isolated action potentials, but it did depress release evoked by action-potential trains. In contrast, a mutation that increased Ca(2+)-dependent phosphatidylinositolbisphosphate binding to the C(2)B domain enhanced release evoked by isolated action potentials and by action-potential trains. Our data suggest that, during repeated action potentials, Ca(2+) and phosphatidylinositolphosphate binding to the Munc13 C(2)B domain potentiate synaptic vesicle exocytosis, thereby offsetting synaptic depression induced by vesicle depletion.
Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Ok-Ho
OH
Shin
Jun
J
Lu
Jeong-Seop
JS
Rhee
Diana R
DR
Tomchick
Zhiping P
ZP
Pang
Sonja M
SM
Wojcik
Marcial
M
Camacho-Perez
Nils
N
Brose
Mischa
M
Machius
Josep
J
Rizo
Christian
C
Rosenmund
Thomas C
TC
Südhof
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004594:Electrophysiology; D005089:Exocytosis / Q000235:genetics / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010743:Phospholipids; D017434:Protein Structure, Tertiary / Q000235:genetics; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D009435:Synaptic Transmission / Q000235:genetics / Q000502:physiology*; D013572:Synaptic Vesicles / Q000235:genetics / Q000378:metabolism*
D009419:Nerve Tissue Proteins; D010743:Phospholipids; C103912:Unc13a protein, rat; D002118:Calcium