1. Kinases and phosphatases work together to regulate cell signaling through phosphorylation and dephosphorylation of proteins. Kinases add phosphate groups while phosphatases remove them, allowing rapid and transient signaling responses.
2. There are three main classes of protein kinases - serine/threonine kinases, tyrosine kinases, and mixed kinases. Key kinase families discussed include PKA, PKC, calcium/calmodulin dependent kinases, receptor tyrosine kinases, and MAP kinases.
3. Phosphatases counteract kinase activity to terminate signaling responses in a timely manner. Important phosphatase families are PP1, PP2A, and calcineurin
1. Kinases and Phosphatases
in cell signaling
Giulio Taglialatela, Ph.D.
John Sealy Professor and Vice Chair
Dept. of Neurology
Director, Mitchell Center for Neurodegenerative Diseases
The University of Texas Medical Branch at Galveston
7. The balanced activity between kinases and
phosphatases provides sudden and (often)
short lived modifications of proteins,
resulting in effective signaling events
57. The ability of intracellular Ca2+
stores to release Ca2+
is
affected by the relative concentration of free cytosolic Ca2+
:
It is increased by slightly elevated Ca2+
and decreased by very
high Ca2+
concentrations.
0
2
4
6
8
10
12
Cytpsolic Ca2+ concentration
ERCa2+release
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70.
71.
72.
73.
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75.
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81.
82.
83.
84. Intracellular Ca2+
increases are characterized by:
- frequency
- amplitude (intensity)
Consequently, cells have developed systems that will respond to
either intensity or frequency (or both) of Ca2+
increases.
85. CaM Kinase II, a direct substrate for calmodulin, is a Ca2+
spike
frequency detector
In order for CaM Kinase to be fully active, each catalytic subunit
must be autophosphorylated in a calmudulin-dependent fashion.
Autophosphorylation of each subsequent subunit follows a co-
operative kinetic.
86. CaM Kinase II, a direct substrate for calmodulin, is a Ca2+
spike
frequency detector
In order for CaM Kinase to be fully active, each catalytic subunit
must be autophosphorylated in a calmudulin-dependent fashion.
Autophosphorylation of each subsequent subunit follows a co-
operative kinetic.
calmudulin
87. CaM Kinase II, a direct substrate for calmodulin, is a Ca2+
spike
frequency detector
In order for CaM Kinase to be fully active, each catalytic subunit
must be autophosphorylated in a calmudulin-dependent fashion.
Autophosphorylation of each subsequent subunit follows a co-
operative kinetic.
88. CaM Kinase II, a direct substrate for calmodulin, is a Ca2+
spike
frequency detector
In order for CaM Kinase to be fully active, each catalytic subunit
must be autophosphorylated in a calmudulin-dependent fashion.
Autophosphorylation of each subsequent subunit follows a co-
operative kinetic.
89. CaM Kinase II, a direct substrate for calmodulin, is a Ca2+
spike
frequency detector
In order for CaM Kinase to be fully active, each catalytic subunit
must be autophosphorylated in a calmudulin-dependent fashion.
Autophosphorylation of each subsequent subunit follows a co-
operative kinetic.
Fully active CaM kinase
107. P
The phophotyrosine domain acts as a docking site for
proteins possessing a particular domain called SH2
SH2
108. P SH2
The SH2-containing protein is then activated by
either conformational change or by phosphorylation
promoted by the receptor itself.
P PLCγ
PI3-K
GAP (GEF)
IRS
109. P SH2
P
PLCγ −> PIP2/IP3/PKC
PI3-K −> IP2/PIP3/PKB
GAP (GEF) −> ras/MAPK
IRS
Multiple pathway activation
129. Both calcineurin and CaMKII are essential
to modulate the function of the synapse in
response to stimulatory Ca++ entry
Both calcineurin and CaMKII are activated
by binding to Ca++/calmodulin
CaMKII is enriched at glutamatergic synapses and assemble into multimers
Activated CaM binds to these units, allowing them to autophosphorylate at T286
A mutation is CaMKII that prevents autophosphorylation blocks LTP (Giese et al. 1998)
Calcineurin is a phosphatase that comprises over 1% of total protein in the brain, and affects many neuronal functions. CaN has been demonstrated to regulate the activity of ion channels, neurotransmitter and hormone release, synaptic plasticity, and gene transcription (Yakel 1997). Studies where the gene is knocked out, knocked down, and overexpressed all result in impaired behavior in rodent models. This suggests that CaN is a critical protein, in moderation. If levels are too low or too high synaptic function can be compromised.