title: Sequestration of CaMKII in dendritic spines in silico.
abstract: Calcium calmodulin dependent kinase II (CaMKII) is sequestered in dendritic spines within seconds upon synaptic stimulation. The program Smoldyn was used to develop scenarios of single molecule CaMKII diffusion and binding in virtual dendritic spines. We first validated simulation of diffusion as a function of spine morphology. Additional cellular structures were then incorporated to simulate binding of CaMKII to the post-synaptic density (PSD); binding to cytoskeleton; or their self-aggregation. The distributions of GFP tagged native and mutant constructs in dissociated hippocampal neurons were measured to guide quantitative analysis. Intra-spine viscosity was estimated from fluorescence recovery after photo-bleach (FRAP) of red fluorescent protein. Intra-spine mobility of the GFP-CaMKIIα constructs was measured, with hundred-millisecond or better time resolution, from FRAP of distal spine tips in conjunction with fluorescence loss (FLIP) from proximal regions. Different FRAP \ FLIP profiles were predicted from our Scenarios and provided a means to differentiate binding to the PSDs from self-aggregation. The predictions were validated by experiments. Simulated fits of the Scenarios provided estimates of binding and rate constants. We utilized these values to assess the role of self-aggregation during the initial response of native CaMKII holoenzymes to stimulation. The computations revealed that self-aggregation could provide a concentration-dependent switch to amplify CaMKII sequestration and regulate its activity depending on its occupancy of the actin cytoskeleton.
authors.affiliation: Laboratory of Neurobiology, National Institute of Neurological Diseases & Stroke, Bethesda, MD 20892, USA. ShahidKhan@mbclss.org
authors.forename: Shahid
authors.initials: S
authors.lastname: Khan
authors.forename: Yixiao
authors.initials: Y
authors.lastname: Zou
authors.forename: Asma
authors.initials: A
authors.lastname: Amjad
authors.forename: Ailia
authors.initials: A
authors.lastname: Gardezi
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Smith
authors.forename: Christine
authors.initials: C
authors.lastname: Winters
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Reese
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000201:enzymology* / Q000378:metabolism; D049229:Dendritic Spines / Q000201:enzymology*; D008959:Models, Neurological; D061251:Primary Cell Culture; D011485:Protein Binding / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology*
chemical_list: D000199:Actins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2