How Neurons Communicate at Synapses
Jose Rizo-Rey
White gives check mate in two moves
Samuel Loyd 1859
So beautiful!
Samuel Loyd 1859
OUR AMAZING BRAIN
http://research.vtc.vt.edu/news/2013/feb/13/brain-awareness-week-designed-highlight-advances-b/
Neurons are the key cells that make the brain so unique
trauma.blog.yorku.ca
arttattler.com
(drawings by Santiago Ramon y Cajal)
Neurons form amazing networks
neuronico.net
www.the-scientist.com
(drawings by Santiago Ramon y Cajal)
The brain is an extremely complex communications network
Interneuronal communication occurs at synapses
Xinran Liu
There are many types of neurons
A common feature is their polarity
biologyboom.com
The membrane potential arises from differences in
the concentrations of ions inside and outside the cell
mikeclaffey.com
Some ion channels can open and close depending on the membrane potential,
and help to propagate electrical signals with a very fast speed
www.emaze.com
a single ion channel opening and closing
aups.org.au
These electrical signals are known as actions potentials and are
propagated by opening and closing of sodium and potassium channels
faculty.washington.edu
Synaptic transmission occurs at synapses
cjonesbvis518.wordpress.com
Chemical synaptic transmission
synaptic vesicles
presynaptic
terminal
action potential
docking
priming
Ca2+
fusion
Ca2+
synaptic cleft
postsynaptic
cell
neurotransmitter
receptors
Binding of neurotransmitters to postsynaptic receptors can cause
excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs),
depending of the type of synapse and the neurotransmitter released
presynaptic
neuron
EPSP
postsynaptic neuron
presynaptic
neuron
7e.biopsychology.com
postsynaptic neuron
IPSP
Different inputs are integrated at the cell body, leading to an action potential
in the axon depending on the balance of the inputs
www.pinterest.com
• Repetitive stimulation can lead to stronger or weaker postsynaptic potentials
• This plasticity can arise from:
presynaptic changes in the efficiency of neurotransmitter release
and/or changes in the postsynaptic responses
• Synaptic plasticity underlies many forms of information processing in the brain
Shin et al. (2010) Nat. Struct. Mol. Biol. 2010 17, 280
The knee-jerk reflex illustrates a behavior
controlled by a system of distinct neurons
bio1152.nicerweb.com
Synaptic vesicle fusion is key for interneuronal communication
synaptic vesicles
presynaptic
terminal
action potential
docking
priming
Ca2+
fusion
Ca2+
synaptic cleft
postsynaptic
cell
neurotransmitter
receptors
Lluis Rizo
Lluis Rizo
Cytoplasm
SNAP
C2B
C2A
NSF
Rabphilin
ZF
Rab3A
Munc13
C2B
Syntaxin
Rim
Synaptic
Vesicle
C2C
Munc18
MUN
C2A
C2A
PDZ
C2B
Rab3A
SNAP-25
ZF
C2B
Synaptotagmin
Synaptobrevin
Plasma Membrane
Synaptic Cleft
Complexin
C2A
C1
Structures and Ca2+ binding modes of the synaptotagmin-1 C2 domains
C2A
Shao et al. Science 273, 248 (1996)
Shao et al. Biochemistry 37, 16106 (1998)
C2B
Ubach et al. EMBO J. 17, 3921 (1998)
Fernandez et al. Neuron 32, 1057 (2001)
Synaptotagmin I acts as a Ca2+ sensor in neurotransmitter release
In vitro Ca2+-dependent
phospholipid binding
In vivo Ca2+-dependence of
neurotransmitter release
Fernandez-Chacon et al. Nature 410, 41 (2001)
Cytoplasm
SNAP
C2B
C2A
NSF
Rabphilin
ZF
Rab3A
Munc13
C2B
Syntaxin
Rim
Synaptic
Vesicle
C2C
Munc18
MUN
C2A
C2A
PDZ
C2B
Rab3A
SNAP-25
ZF
C2B
Synaptotagmin
Synaptobrevin
Plasma Membrane
Synaptic Cleft
Complexin
C2A
C1
The SNARE complex
N
Habc-domain
Synaptic
vesicle
synaptobrevin
syntaxin
SNAP25
C
N
Plasma membrane
Sutton et al. (1998) Nature 395, 347
Fernandez et al. (1998) Cell 18, 841
Widespread, SNARE-centric model of synaptic vesicle fusion
Synaptic
vesicle
Synaptic
vesicle
Syntaxin-1(open)/SNAP-25
Synaptobrevin
Syntaxin-1
(closed)
Synaptobrevin
SNAP-25
Plasma membrane
Vesicle
recycling
NSF/SNAPs
SNARE complex
Model for how synaptotagmin cooperates with the SNAREs
to induce calcium-dependent membrane fusion
synaptotagmin
Ca2+
C2A
--
--
C2B
-
--
-
--
LIPID MIXING ASSAY TO STUDY MEMBRANE FUSION IN VITRO
1.8
1.6
I538/I589
1.4
1.2
1.0
0.8
0.6
0.4
0
50
100
Time (mins)
150
Weber et al. (1998) Cell 92, 759
Efficient membrane fusion in vitro with SNAREs and Synaptotagmin-1
SNAREs + Ca2+
+ Synaptotagmin-1
SNAREs alone
Tucker et al. Science 304, 435 (2004)
Chicka et al. Nat. Struct. Mol. Biol. 15, 827 (2008)
Xue et al. Nat. Struct. Mol. Biol. 15, 1160 (2008)
But without Munc18-1 or Munc13!
Total abrogation of neurotransmitter release
In the absence of Munc18-1 or Munc13s
Munc18-1 KO
Total silence
control
Munc18-1 KO
Verhage et al. Science 287, 864 (2000)
Munc13-1/2 KO
Total silence
control
Munc13-1/2 DKO
Varoqueaux et al. Proc. Natl. Acad. Sci. U. S. A 99, 9037 (2002)
Model of Munc18-1 and Munc13 function
synaptobrevin
Munc18-1
++
+
++
+
+ + +
syntaxin
closed
++
+
+++
+ + +
SNAP-25
++ +
+
+
+
+
+
Fernandez et al. Cell 18, 841 (1998)
Carr et al. J. Cell Biol. 146, 333 (1999)
Dulubova et al. EMBO J. 21, 3620 (2002)
Dulubova et al. PNAS 104, 2697 (2007)
Xu et al., Biochemistry 49, 1568 (2010)
+ ++
Munc13
MUN domain
++
+
++
+
+++
+
+ + +
++
+
+ + +
Dulubova et al. EMBO J. 18, 4372 (1999)
Yamaguchi et al. Developmental Cell 2, 295 (2002)
Dulubova et al. PNAS 100, 32 (2003)
Deak, Xu et al., J. Cell. Biol. 184, 751 (2009)
Ma et al., Nat. Struct. Molec. Biol. 18, 542 (2011)
Reconstitution of membrane fusion with Syntaxin-1/Munc18-1 liposomes
+ Synaptobrevin liposomes
+ Munc13-1, SNAP-25 and Synaptotagmin-1
Synaptobrevin
D
A
Syntaxin-1
Fluorescence (% of max)
Munc18-1
30
+SNAP-25+synaptotagmin+
Munc13-1
20
10
0
0
500
+Synaptotagmin+Munc13-1
+SNAP-25+
Synaptotagmin
+SNAP-25+Munc13-1
1000
1500
2000
2500
Time (s)
Ma et al. Science 339, 421 (2013)
Efficient fusion with Syntaxin-1/SNAP-25 liposomes
+ Synaptobrevin liposomes
+ Synaptotagmin-1
Synaptobrevin
D
+
A
SNAP-25
Syntaxin-1
Fluorescence (% of max)
40
30
+synaptotagmin
20
10
0
0
500
1000
Time (s)
1500
2000
2500
Ma et al. Science 339, 421 (2013)
Fusion with Syntaxin-1/SNAP-25 liposomes
+ Synaptobrevin liposomes + Synaptotagmin-1
is inhibited by NSF, a-SNAP
Synaptobrevin
D
+
A
SNAP-25
Syntaxin-1
Fluorescence (% of max)
40
30
+synaptotagmin
20
10
0
+synaptotagmin+NSF/aSNAP+ATP
0
500
1000
Time (s)
1500
2000
2500
Ma et al. Science 339, 421 (2013)
Reconstitution of synaptic vesicle fusion
with Syntaxin-1/SNAP-25 liposomes + Synaptobrevin liposomes
+ Munc18-1, Munc13-1, NSF, a-SNAP and Synaptotagmin-1!!!!!
Synaptobrevin
D
+
A
SNAP-25
Syntaxin-1
Fluorescence (% of max)
40
+synaptotagmin+NSF/aSNAP+ATP
+M18+Munc13-1
30
+synaptotagmin
20
10
+synaptotagmin+NSF/aSNAP
+ATP+Munc13-1
0
+synaptotagmin+NSF/aSNAP+ATP
0
500
1000
Time (s)
1500
2000
WE GOT IT!
2500
Ma et al. Science 339, 421 (2013)
Highly efficient calcium-dependent membrane fusion supported by the SNARES,
Synaptotagmin-1, Mun18-1, Munc13-1, Synaptotagmin-1 and NSF-a-SNAP
Synaptobrevin
D
synaptotagmin
A
SNAP-25
Syntaxin-1
Lipid mixing
Content mixing T+VSyt1 +NSF/aSNAP
Ca2+
Ca2+
+Munc13-1+Munc18-1
20
10
+Munc18-1
0
+Munc13-1
T+VSyt1
0
500
1000 1500
Time (s)
2000
2500
100
Fluorescence (% of max)
Fluorescence (% of max)
30
T+VSyt1 +NSF/aSNAP
+Munc13-1+Munc18-1
80
60
40
20
+Munc13-1
+Munc18-1
T+VSyt1
0
0
500
1000 1500
Time (s)
2000
2500
Xiaoxia Liu, Alpay Seven
Model of synaptic vesicle fusion integrating the functions of
SNAREs, Munc18-1, Munc13s, NSF/SNAPs and synaptotagmin-1
Synaptotagmin-1
Synaptic
vesicle
Syntaxin-1(open)/SNAP-25
NSF/SNAPs
+ Munc18-1
Munc18-1
Syntaxin-1
(closed)
Synaptobrevin
SNAP-25
Munc18-1
Plasma membrane
Munc13
Ca2+
Munc13
Ma et al. Science 339, 421 (2013)