title: Mass of the postsynaptic density and enumeration of three key molecules.
abstract: The total molecular mass of individual postsynaptic densities (PSDs) isolated from rat forebrain was measured by scanning transmission EM. PSDs had a mean diameter of 360 nm and molecular mass of 1.10 +/- 0.36 GDa. Because the mass represents the sum of the molecular masses of all of the molecules comprising a PSD, it becomes possible to derive the number of copies of each protein, once its relative mass contribution is known. Mass contributions of PSD-95, synapse-associated protein (SAP)97, and alpha-Ca2+/calmodulin-dependent protein kinase II (CaMKII) were determined by quantitative gel electrophoresis of PSD fractions. The number of PSD-95 molecules per average PSD, contributing 2.3% of the mass of the PSD, was calculated to be 300, whereas the number of SAP97 molecules, contributing 0.9% of the mass of the PSD, was 90. The alpha-CaMKII holoenzymes, which contribute 6% of the mass when brains are homogenized within 2 min of interrupting blood flow, have 80 holoenzymes associated with a typical PSD. When blood flow is interrupted 15 min before homogenization, the average mass of PSDs increases by approximately 40%. The additional alpha-CaMKII associated with PSDs accounts for up to 20% of this mass increase, representing the addition of 100-200 alpha-CaMKII holoenzymes.
authors.affiliation: Laboratory of Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 36 Convent Drive, MSC 4062, Bethesda, MD 20892, USA.
authors.forename: Xiaobing
authors.initials: X
authors.lastname: Chen
authors.forename: Lucia
authors.initials: L
authors.lastname: Vinade
authors.forename: Richard D
authors.initials: RD
authors.lastname: Leapman
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Petersen
authors.forename: Terunaga
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Terry M
authors.initials: TM
authors.lastname: Phillips
authors.forename: Morgan
authors.initials: M
authors.lastname: Sheng
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Reese
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000302:isolation & purification; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure; D004586:Electrophoresis; D008565:Membrane Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure; D008854:Microscopy, Electron; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000648:ultrastructure; D016548:Prosencephalon / Q000166:cytology / Q000378:metabolism*; D051381:Rats
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501119:Dlg1 protein, rat; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; C033652:postsynaptic density proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases