PSYC 310 Lecture Notes - Lecture 16: Radial Arm Maze, Insular Cortex, Intron
7 May 2018
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PSYC 318: Wednesday March 28th, 2018
Persistent Protein Kinases
• Learning objectives
o PKA
o CAMKII
o PKC
▪ Details about molecular structure of these proteins
o How to test whether persistent kinases are involved in maintenance of memory
▪ So far we’ve talked mainly about induction of memory
▪ Learning induces changes in brain
▪ These changes have to be maintained for periods of time
o Specific model for how persistent phosphorylation increases AMPA receptor levels by
blocking endocytosis of receptors – active model for how memories are maintained
o Issues with zeta inhibitory peptide (ZIP)
▪ Specificity might not be as specific as people thought
▪ Compensation in Zeta KO mice
▪ Differences in aplysia and vertebrates in how persistent PKCs (PKMs) are made
• Different biochemical traces can be graded by their ‘volatility’
o Persistent activation of protein kinases
o Reversibility depends on mechanism for persistence
• What is a protein kinase
o Takes phosphate from ATP, alters protein function
• Short term memory reflects activation of protein kinases
o CAMKII activated by calcium influx through NMDA receptors
o Calcium activates CAMKII which phosphorylates proteins, increases # of AMPA
receptors at synapses
o Cyclic AMP activated protein kinase through g-protein coupled receptors
• How kinases become persistently active: the structure of these protein kinases
o All 3 protein kinases share similarities in how they’re regulated
o They all contain a regulatory part and a catalytic part
▪ Catalytic domain sufficient to phosphorylate substrate
▪ Regulatory determines when kinase active
o Inhibit catalytic domain with sequence in regulatory that looks like a substrate but can’t be
phosphorylated
o Pseudo-substrate prevents it from phosphorylating target proteins
• Protein Kinase structures
o Second messengers bind to regulatory subunits of kinases and cause conformational
changes that activate those kinases
▪ These activations only last as long as second messengers act
▪ Become persistently active not due to persistent production of second
messengers
▪ Not the mechanism thought to underlie persistent activation of protein kinases
o Many of these kinases are regulated by phosphorylation in catalytic domain
▪ Constitutive
▪ Even though they’re regulated and need phosphorylation, that phosphorylation is
not regulated
▪ Constitutively active = persistently active (interchangeable)
o These kinases are anchored to their substrate through anchoring proteins that bring them
close to their substrates
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▪ Important determinant of substrate specificity based on shape of catalytic domain
and what amino acids fit into it
o Removal of the action of the regulatory subunit
▪ Distinct mechanism between 3 protein kinases: how they remove regulatory
subunit from inhibiting catalytic subunit
o How are specific kinases activated/persistently activated?
▪ PKA has separate regularly (r) and catalytic (c) subunits (diff genes)
▪ cAMP binding causes disassociation of subunits
▪ in aplysia, the main place that persistent activation of PKA has been studied,
persistent activity due to degradation of regulatory subunit
▪ less regulatory subunit: ratio between catalytic subunit:regulatory subunit off,
more c subunit more persistently active PKA
o Diagram:
▪ Red circle is c subunit
▪ Green lines r subunit
▪ Cyclic AMP binds to r subunit and causes disassociation of c subunit
o Testing maintenance
▪ For maintenance of LTF
▪ One needs a way of disassociating induction of memory from maintenance of
memory
▪ If you block induction of memory you block maintenance
▪ You have to inhibit it after memory was formed and see if memory was erased
▪ Erasing memory mechanism for testing of maintenance of memory
o Inhibitor of PKA blocks memory for about 12 hours after learning
▪ Long-term increase in synaptic strengths
▪ Measure initial increase in neuron, re-examine synaptic strengths later in
presence of inhibitor of PKA
▪ What % of increase in synaptic strengths depends on continued presence of
PKA?
▪ Immediately after learning almost all increase of synaptic strength removed with
inhibitory of PKA all the way up to 12 hours after induction of memory: sizable
proportion of the memory that increases synaptic strengths mediated by
persistent activation of PKA
▪ PKA inhibitor added right before measurement, wasn’t present the whole time
▪ At 24 hours after
• PKA no longer maintaining the memory, persistent activation of PKA
• Inhibiting PKA no longer affects increase of synaptic strength you see at
24 hours
• Inhibitors of PKA only block LTF for 12 hours, and even then only a
certain % of LTF being blocked
• Memory trace changes over time
o CAMKII
▪ Calcium-calmodulin kinase II is a dodecamer (12 subunits)
• PKA was a dimer (2 subunits)
▪ Activated by calcium influx
• Calcium binds to calmodulin and 2 together bind kinase and activate it
▪ Becomes constitutively active due to phosphorylation by an adjacent subunit
• A phosphorylation between the region between regulatory and
catalytic domain
• Auto-phosphorylation done by CAMKII itself
o Not a cis-autophosphorylation
find more resources at oneclass.com
find more resources at oneclass.com
