Simulating Electron Paramagnetic Resonance Spectra of Slow-Motion Systems in the Time Domain

Abstract

cations. A discrete set of high probability binding sites were identified at the interface between catalytic and association domains of neighboring subunits, far from the Mg 2þ binding sites required to coordinate ATP in the catalytic cleft. Next, we experimentally characterized the effects of divalent cations on CaMKII structure using fluorescence, light scattering and electron microscopy. We found that some, but not all, divalent ions including Zn 2þ promote the reversible formation of self-assembled CaMKII fibers that can extend for several mm. When associated in fibers, CaMKII activity is compromised; however, Ca 2þ /CaM activation of the enzyme disassembles fibers and the loss of activity is reversed. Interestingly, fiber assembly does not interfere with the autophosphorylation of CaMKII at T286, an autoregulatory modification, which confers autonomous activity in monodisperse CaMKII. We compile our results with structural and mechanistic data from literature to propose a model of Zn 2þ -mediated CaMKII fiber formation, where Ca 2þ /CaM regulates fiber formation through allosteric modification of a divalent ion site identified in our electrostatic map.

A Global Minimization Toolkit for Batch-Fitting and χ2 Cluster Analysis of CW-EPR Spectra

“…Since the introduction of these software packages, the SLE model has been enhanced by incorporating the macroscopic order microscopic disorder (MOMD) model and the slowly relaxing local structure (SRLS) model (23,24). The validity of the SLE model in the slow-motion regime has been verified by molecular dynamics simulations, which can accurately reproduce EPR spectra from atomistic trajectory files and confirm that the diffusion of spin labels gives an accurate approximation of the dynamics of the local environment (25)(26)(27)(28)(29).…”