Synaptotagmin I functions as a calcium regulator of release probability.
In all synapses, Ca2+ triggers neurotransmitter release to initiate signal transmission. Ca2+ presumably acts by activating synaptic Ca2+ sensors, but the nature of these sensors--which are the gatekeepers to neurotransmission--remains unclear. One of the candidate Ca2+ sensors in release is the synaptic Ca2+-binding protein synaptotagmin I. Here we have studied a point mutation in synaptotagmin I that causes a twofold decrease in overall Ca2+ affinity without inducing structural or conformational changes. When introduced by homologous recombination into the endogenous synaptotagmin I gene in mice, this point mutation decreases the Ca2+ sensitivity of neurotransmitter release twofold, but does not alter spontaneous release or the size of the readily releasable pool of neurotransmitters. Therefore, Ca2+ binding to synaptotagmin I participates in triggering neurotransmitter release at the synapse.
Fernández-Chacón
R
R
Center for Basic Neuroscience, Department of Molecular Genetics, and Howard Hughes Medical Institute, The University of Texas Southwestern Medical Center, Dallas 75390-9111, USA.
Königstorfer
A
A
Gerber
S H
SH
García
J
J
Matos
M F
MF
Stevens
C F
CF
Brose
N
N
Rizo
J
J
Rosenmund
C
C
Südhof
T C
TC
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017354:Point Mutation; D011485:Protein Binding; D011487:Protein Conformation; D013569:Synapses / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism; D050863:Synaptotagmin I; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D050863:Synaptotagmin I; C494311:Syt1 protein, mouse; D050857:Synaptotagmins; D002118:Calcium