Structure of the Autoinhibited Kinase Domain of CaMKII and SAXS Analysis of the Holoenzyme

Abstract

Ca2+/calmodulin-dependent protein kinase-II (CaMKII) is unique among protein kinases for its dodecameric assembly and its complex response to Ca2+. The crystal structure of the autoinhibited kinase domain of CaMKII, determined at 1.8 A resolution, reveals an unexpected dimeric organization in which the calmodulin-responsive regulatory segments form a coiled-coil strut that blocks peptide and ATP binding to the otherwise intrinsically active kinase domains. A threonine residue in the regulatory segment, which when phosphorylated renders CaMKII calmodulin independent, is held apart from the catalytic sites by the organization of the dimer. This ensures a strict Ca2+ dependence for initial activation. The structure of the kinase dimer, when combined with small-angle X-ray scattering data for the holoenzyme, suggests that inactive CaMKII forms tightly packed autoinhibited assemblies that convert upon activation into clusters of loosely tethered and independent kinase domains.

Structural rearrangement of CaMKIIα catalytic domains encodes activation

“…Regardless, it demonstrates the importance of verifying structural details with multiple approaches and under physiological conditions. By using X-ray crystallography, the Kuriyan group also demonstrated that autoinhibited catalytic domains isolated from Escherichia coli expressing a truncated Caenorhabditis elegans CaMKII (residues 1-340 of Unc-43) form dimers (12). A surprising feature of this dimer structure was that ATP access to the kinase ATPbinding site was occluded.…”

“…Each CaMKII subunit is composed of an N-terminal catalytic domain, a regulatory domain, and a C-terminal association domain, that assemble to form a holoenzyme whose structure has been extensively studied in vitro (10)(11)(12)(13)(14)(15). Electron microscopy (EM) imaging of single particles of CaMKII isolated from rat brain revealed ''flower-like'' structures with association domains in a central core and catalytic domains radiating out like petals (15).…”

Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) is activated by calmodulin with two bound calciums

“…CaMKII is a dodecameric oligomer of catalytic subunits, each of which can bind one CaM (21)(22)(23). Binding of CaM to an individual subunit activates its kinase activity allowing the subunit to phosphorylate other proteins.…”

Ischemia-elicited Oxidative Modulation of Ca2+/Calmodulin-dependent Protein Kinase II

“…In the central nervous system, CaMKII plays a pivotal role in the facilitation of synaptic plasticity, learning, and memory and in activity-dependent developmental processes (1). CaMKII holoenzyme is a dodecamer composed of two stacked hexameric rings, in which each catalytic/regulatory domain from the upper ring interacts with the equivalent catalytic/regulatory domain in the lower ring by an antiparallel coiled-coil, which resides in regulatory domains (2). Binding of Ca 2ϩ /CaM to the regulatory domain separates the dimer pair and causes the exposure of Thr-286 or Thr-287 (within ␣ or ␤ subunit) for phosphorylation by another catalytic domain in the same ring.…”

“…Ca 2ϩ /calmodulin (CaM) 2 -dependent protein kinase II (CaMKII) is one of the major Ca 2ϩ -sensing enzymes important in transducing neuronal, hormonal, and electrical signals in brain, heart, and other tissues. In the central nervous system, CaMKII plays a pivotal role in the facilitation of synaptic plasticity, learning, and memory and in activity-dependent developmental processes (1).…”