title: Distribution of postsynaptic density (PSD)-95 and Ca2+/calmodulin-dependent protein kinase II at the PSD.
abstract: Postsynaptic densities (PSDs) contain proteins that regulate synaptic transmission. We determined the positions of calcium/calmodulin-dependent protein kinase II (CaMKII) and PSD-95 within the three-dimensional structure of isolated PSDs using immunogold labeling, rotary shadowing, and electron microscopic tomography. The results show that all PSDs contain a central mesh immediately underlying the postsynaptic membrane. Label for PSD-95 is found on both the cytoplasmic and cleft sides of this mesh, averaging 12 nm from the cleft side. All PSDs label for PSD-95. The properties of CaMKII labeling are quite different. Label is virtually absent on the cleft sides of PSDs, but can be heavy on the cytoplasmic side at a mean distance of 25 nm from the cleft. In tomograms, CaMKII holoenzymes can be visualized directly, appearing as labeled, tower-like structures reflecting the 20 nm diameter of the holoenzyme. These towers protrude from the cytoplasmic side of the central mesh. There appears to be a local organization of CaMKII, as judged by fact that the nearest-neighbor distances are nearly invariant over a wide range of labeling density for CaMKII. The average density of CaMKII holoenzymes is highly variable, ranging from zero to values approaching a tightly packed state. This variability is significantly higher than that for PSD-95 and is consistent with an information storage role for CaMKII.
authors.affiliation: Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Petersen
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Chen
authors.forename: Lucia
authors.initials: L
authors.lastname: Vinade
authors.forename: Ayse
authors.initials: A
authors.lastname: Dosemeci
authors.forename: John E
authors.initials: JE
authors.lastname: Lisman
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Reese
mesh_terms: D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000032:analysis*; D000076122:Disks Large Homolog 4 Protein; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D008854:Microscopy, Electron / Q000379:methods; D009419:Nerve Tissue Proteins / Q000032:analysis*; D016548:Prosencephalon / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000737:chemistry / Q000648:ultrastructure; D013569:Synapses / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C033652:postsynaptic density proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases