Do CaMKII holoenzymes hide inside postsynaptic densities?

Tuesday, October 25, 2011 — Poster Session II
Noon – 2:00 p.m.	Natcher Conference Center	NINDS	STRUCTBIO-3

Authors

• A Fera
• A Dosemeci
• P Gallant
• T Reese

Abstract

Postsynaptic densities (PSDs) from rat forebrain have been examined by negative stain tomography with a stain (NanoW) that tolerates large electron doses and provides information from the full thickness of a PSD (~40 nm). CaMKII holoenzymes are identified in tomograms by their association domains, which match those in recombinant CaMKII molecules. Identification of association domains makes it possible to map individual holoenzymes in PSDs without resorting to immunolabeling. The cleft and cytoplasmic sides of PSDs can be readily distinguished in negative stain tomograms. Plots of distributions of assembled association domains in six PSDs shows that approximately a third of the holoenzymes line the cytoplasmic surface of PSDs while the rest are distributed throughout their thickness, while their radial distribution appears even. CaMKII molecules both singly and in clusters have previously been reported at cytoplasmic surfaces of PSDs. The new finding here is that many holoenzymes are distributed throughout the core of the PSD. These data are compatible with CaMKII holoenzymes being anchored at specific locations in the PSD, ready to phosphorylate specific components. Negative stain tomography can be scaled down to determine the distribution of CaMKII in PSDs isolated from slice cultures, where the exactly physiological conditions can be controlled.

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