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Abstract:
Synaptotagmin-1 is the main Ca
2+
-
s
ensor of neuronal exocytosis. It binds to both
Ca
2+
and the anionic phospholipid
p
hosphatidylinositol 4,5-bisphosphate (PIP2),
but the precise cooperativity of this binding is
still poorly understood. Here, we used
microscale thermophoresis (MST) to quantify
the cooperative binding of PIP2 and Ca
2+
to
s
ynaptotagmin-1. We find that PIP2 binds to
the well-conserved polybasic patch of the
C2B-domain with an apparent dissociation
constant of ~20 μM. PIP2-binding reduces the
apparent dissociation constant for Ca
2+
from
~
250 μM to < 5 μM. Thus, our data show that
PIP2 makes synaptotagmin-1 > 40-fold more
sensitive for Ca
2+
. This interplay between
C
a
2+
, synaptotagmin-1 and PIP2 is crucial for
n
eurotransmitter release.
