CaMKII: some basics to remember

The theme of Thursday’s Volen Center for Complex Systems annual retreat will be Breakthroughs in understanding the role of CaMKII in synaptic function and memory and honors the pioneering work of John Lisman. To help bring non-experts up to speed, we asked Neuroscience Ph.D. students Stephen D. Alkins and Johanna G. Flyer-Adams from the Griffith lab at Brandeis for a quick primer on CaMKII.

What’s a protein kinase? 

Protein kinases are enzymes that act by adding phosphate groups to other proteins – a process called phosphorylation. Phosphorylation of a protein usually initiates a cascade of downstream effects such as changes in the protein’s 3D shape,  changes in its interactions with other proteins, changes in its activity and changes in its localization. In causing these types of changes, kinases facilitate some of the most essential cellular and molecular processes required for survival and proper functionality.

Aren’t there lots of protein kinases? What makes CaMKII special? 

Among the roughly 500+ genes in the human genome encoding protein kinases, a kinase known as calcium (Ca2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylates serine or threonine residues in a broad array of target proteins.  Though found in many different tissues (skeletal muscle, cardiac muscle, spleen, etc.), there is a lot of CaMKII in the brain– about 1% of total forebrain protein and 2% of total hippocampal protein (in rats). Previous research, including pivotal contributions from the Lisman Lab at Brandeis University working in mammalian brain, has identified CaMKII as a cellular and molecular correlate of learning and memory through its multiple roles governing normal neuronal structure, synaptic strength, plasticity, and homeostasis. The Griffith Lab has been instrumental in demonstrating that these roles of the kinase are conserved in invertebrates.

Why do we think CaMKII might play a role in memory?

a) Location!

As previously mentioned, CaMKII accounts for up to 2% of all proteins in memory-important brain regions like the hippocampus. It’s also highly abundant at neuronal synapses, where neurons communicate with each other.

b) Function!

Memory is thought to require a process called long term potentiation (LTP) where two neurons, in response to environmental changes, will change the strength of the synaptic connections by which they communicate with each other—these changes will last even after the environmental input has disappeared. We know that CaMKII is required for LTP. We also know that the increases in neuronal calcium levels that accompany neuronal activation and cause LTP also allow CaMKII to phosphorylate itself. This autophosphorylation of CaMKII changes its kinase activity so that CaMKII can stay active well past the window of neuronal activation, essentially ‘storing’ the memory of previous neuronal activity—much like LTP!

c) Structure!

Ultimately, the issue with ‘molecular memory’ is that all proteins degrade over time, causing one to ask how we can remember things for so long when the original proteins that stored that memory no longer exist. CaMKII is such an exciting candidate for molecular memory because it is mostly found as a dodecameric holoenzyme—this means that CaMKII likes to exist as a big assembly of twelve identical CaMKII subunits. However, each CaMKII subunit retains its kinase activity even when all twelve are assembled. What’s interesting is that the autophosphorylation and activation of one CaMKII subunit (which happens when neurons are activated and intracellular calcium levels rise) actually makes it easier for the other CaMKII subunits in the twelve-unit holoenzyme to become autophosphorylated and activated. This means that maybe when an activated subunit is old and get degraded, another new CaMKII subunit could take its place among the twelve-unit holoenzyme—and become activated just like the old subunit, allowing for the ‘molecular memory’ to last beyond when proteins degrade!

CaMKII phosphorylation and activationCaMKII in more detail…

Calcium binds to the small protein calmodulin and forms (Ca2+/CaM), which acts as a ‘second messenger’ that increases in concentration when neurons are activated. CaMKII relies on calcium/calmodulin (Ca2+/CaM) binding to activate an individual domain containing a regulatory segment.  In conditions of low calcium, elements within the CaMKII regulatory segment will have less affinity for (Ca2+/CaM) binding, keeping CaMKII in an autoinhibited state.  In conditions of high calcium, (Ca2+/CaM) binding initiates phosphorylation at three threonine residue sites, including Thr286 which prevents rebinding of the regulatory segment, thus keeping CaMKII constitutively active even when calcium levels fall.  In this activated state CaMKII can autophosphorylate inactivated intra-kinase domains, and will undergo subunit exchange with neighboring inactivated CaMKII holoenzymes. Furthermore, mutation of CaMKII residues or binding sites in target proteins, such as postsynaptic glutamate (AMPA) receptors, disrupts establishment of long-term potentiation (LTP) in neurons.  Together, CaMKII’s role as molecular switch that bidirectionally, and autonomously regulates activity in neurons has earned it the illustrious title of a “memory molecule.”

What amino-acid manipulations might I hear about?

a) T286A:

Changing a threonine in a phosphorylation site to an alanine prevents phosphorylation at that site. Blocking Thr286 phosphorylation with a T286A mutation prevents CaMKII generation of autonomous activity that disrupts neuronal activity and results in learning deficits.

b) T286D:

Changing a threonine to an aspartate puts a negative charge at the site, often making it act like it’s always phosphorylated. In the case of CaMKII, a T286D mutation renders the kinase constitutively active, which can interrupt normal LTP induction and normal memory storage and acquisition.

To learn more:

Waltz Symposium on Sept 23

Artificial Intelligence luminaries from across the nation gathered at Brandeis on Sunday Sept 23 to honor David Waltz, who was a professor at Brandeis from 1984-1993 and who passed away in March from cancer. Organized by Prof. Jordan Pollack with sponsorship from Brandeis, AAAI, and Ab Initio Software, the day long event featured keynotes and panels from 6 different phases of Waltz’s career reflecting on his work and his leadership. A complete schedule follows the break and video, when available, is on the Computer Science website.

What’s behind the curtain

Thanks to a gift from Vertica, an HP company, the Department of Computer Science is doing some remodeling in the Volen Center, creating a modern computer laboratory lounge for our students. Classroom 105 is being moved to Volen 119, formerly known as the Berry Patch; Rooms 104 and 105 are being combined and fit with soft furniture, workstations, and group work tables as a comfortable place to sit and work individually and on group projects. We are also upgrading the furniture in the Volen lobby itself.

 

 

 

The CS Systems Operations page says:

2011-06-15: The Berry Patch […] will be closing for renovations on 6/17/2011. The workstations in room 118 next door will remain available, as will the remote shell servers (coeus and themis); several other workstations will also be accessible for remote-only use.

The Volen Center for Complex Systems Retreat, 2011

(co-written by Tilman Kispersky)

Introduction and Location

The annual Volen Center Retreat was held this week at the bucolic Warren Conference Center and Retreat in Ashland, Massachusetts.  The purpose of the one-day retreat is to provide a forum for conversation and encourage collaborations between members of the Brandeis and Volen center research communities.   Funded by the M.R. Bauer Foundation, the retreat features a distinguished invited speaker, lectures from Volen faculty that highlight the diversity of Neuroscience research at the Center and a poster session covering ongoing research projects of the members of the community.

The director of the Volen Center, Prof. Arthur Wingfield began the proceedings with a brief history of the retreat which is in its 17th consecutive year.  While historically the most common location for the retreat has been the Marine Biological Labs in Woods Hole, MA the retreat was held at the 220 acre property of the Warren Conference Center outside of Framingham this year.  Prof. Wingfield introduced the theme of the retreat: “Imaging: Recent breakthroughs in visualization – from synapses to circuits”.  Each lecture focused on data collected with advanced imaging techniques and highlighted how advanced optical methods had enabled a deeper understand of nervous system.

Lectures

The first lecture was given by Prof. Aniruddha Das from the Columbia University Department of Neuroscience.  Prof. Das’ research group developed a method to perform dual-wavelength imaging to measure both the volume of blood present in a given region of cortex as well as the oxygenation level of that blood, two quantities that are combined in traditional fMRI imaging.  Using dual-wavelength imaging Prof. Das found a task-related anticipatory haemodynamic signal in the visual cortex of awake monkeys.  This signal was unrelated to either single unit activity or any visual stimulation.  The finding suggests that cortical circuits increase their blood oxygenation level prior to the expected onset of a task in anticipation of the increased computational load.

The second speaker was Brandeis Professor Stephen Van Hooser.   Prof. Van Hooser studies motion detection in the visual system and is specifically interested in how motion selectivity develops and what role sensory inputs play in this process.  The ferret visual system, the animal model used by Prof. Van Hooser, develops orientation selectivity prior to receiving any sensory input.  However, motion selectivity requires visual inputs and thus develops later, after young ferrets open their eyes.  Prof. Van Hooser presented experimental results that employed two-photon imaging to simultaneously measure the activation of hundreds of cells at depths of up to 300 um beneath the cortical surface.  By presenting moving visual stimuli Prof. Van Hooser was able to track the emergence of motion selectivity in cortical neurons and was able to influence the course of development by changing the direction of motion of the stimulus.

Following the mid-day poster session, the afternoon portion of the retreat featured a trio of talks covering some of the cutting-edge imaging work currently being done at Brandeis.  First up was Dr. Avital Rodal (pictured at right), whose lab employs an innovative, high speed confocal microscopy technique to capture high-resolution images of tagged endosomes on the move in developing fly neurons.  By combining different markers in the same experiment, Dr. Rodal has been able to demonstrate transient interactions, undetectable by traditional methods.  Potentially, her work could help us understand a range of health issues in which endosomal trafficking has been implicated, including neurodegenerative disease and mental retardation.  See the moving endosomes for yourself in a recent blog post covering her exciting work!

The next speaker was able to remind us that sometimes it takes more than biologists to do biology — especially when the task is high-throughput image analysis.  Dr. Pengyu Hong, an Assistant Professor of Computer Science here at Brandeis, shared some of his work using High Content Screening, an automated method of analyzing image data and extracting information about cellular phenotypes and neurite length from images of cell cultures.  Using data provided by his collaborators around the world, his method is able to quantify neuronal morphology, allowing for high throughput genetic and drug discovery screening at improved levels of accuracy — a previously intractable task.

The final speaker of the retreat shared with us an intriguing work in progress.  Dr. David DeRosier (pictured at left), Brandeis Emeritus Professor of Biology, currently a member of the Turrigiano lab, has been developing an imaging technique called “Cryo-PALM”. If it sounds cool, it’s much more than that; it involves holding a biological sample frozen at no more than -140C, while imaging it with a room temperature microscope objective less than a millimeter away.  It sounds difficult — and as David told us, it is! — but the potential is huge.  Dr. DeRosier hopes to be able to precisely localize fluorescently labeled proteins in the synapse down to sub-nanometer resolution, and provide the most detailed picture ever of synaptic structure.

This year’s Volen center retreat was another success, with lots of informative talks, informal mingling, and even delicious food!

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