Thomas Reese, M.D.
Senior Investigator
Department of Neurobiology
NIH
(October 12, 2017)
A Structural View of CaMKII in the Molecular Organization of the PSD
The formation of memories requires changes at the level of the synapse, changes to numbers of receptors, and changes to the shapes of dendritic spine synapses. Memory formation also requires certain enzymes, such as CaMKII. In his presentation, Doctor Reese discussed his research using electron microscopy to determine where CaMKII is localized in the core of the spine synapse, and how the positioning could affect memory formation.
The Reese laboratory investigates the molecular organization of synapses in the brain where memories are created and stored. Specifically, transmission of signals at these synapses depends on glutamate receptors, and changes in efficacy ensue when the numbers of spine receptors are adjusted up or down during synaptic activity. Changes in the numbers of receptors are accompanied by changes in the shapes of the spine synapses and they are interested in finding out what changes in the shapes, numbers and deployments of proteins in synaptic spines support the changes in efficacity.
John Lisman, whom we are honoring, made a major advance on this problem when he predicted and then demonstrated that an enzyme in the synaptic spine, CaMKII, undergoes dramatic changes during the first stages of learning, and that these changes are both necessary and sufficient for learning. Reese’s work shows where CaMKII is localized in the spine so it can interact with receptors and the rest of the spine synaptic machinery.
In detail, he developed two methods to examine the distribution of CaMKII at spine synapses. The first involved biochemically isolating the cores of the spine synapse, known as the post synaptic density, or PSD. He then used a freeze dry/replica method that allowed him to use an antibody to attach gold particles to CaMKII molecules in the PSD, which show up clearly in the electron microscope. He found that much CaMKII forms large complexes clinging to the back surfaces of the PSDs, which may have a mechanical function or even buffer key control components such as calmodulin. Lisman was very intrigued with these CaMKII aggregates and many discussions of their function ensued.
CaMKII is an oligomer and has a 12-member ring at its base. Reese developed a method using a special negative stain to show these rings in the electron microscope and then we could use them to map the positions of CaMKII in the PSD. He found that a portion of the CaMKII in the PSD is situated in positions where it could regulate the function of receptors. Thus, this piece of the puzzle fell into place –we could see directly how CaMKII could affect the initiation of memories.