Oligomerization states of the association domain and the holoenyzme of Ca²⁺/CaM kinase II

Abstract

Ca2+/calmodulin activated protein kinase II (CaMKII) is an oligomeric protein kinase with a unique holoenyzme architecture. The subunits of CaMKII are bound together into the holoenzyme by the association domain, a C‐terminal region of ≈ 140 residues in the CaMKII polypeptide. Single particle analyses of electron micrographs have suggested previously that the holoenyzme forms a dodecamer that contains two stacked 6‐fold symmetric rings. In contrast, a recent crystal structure of the isolated association domain of mouse CaMKIIα has revealed a tetradecameric assembly with two stacked 7‐fold symmetric rings. In this study, we have determined the crystal structure of the Caenorhabditis elegans CaMKII association domain and it too forms a tetradecamer. We also show by electron microscopy that in its fully assembled form the CaMKII holoenzyme is a dodecamer but without the kinase domains, either from expression of the isolated association domain in bacteria or following their removal by proteolysis, the association domains form a tetradecamer. We speculate that the holoenzyme is held in its 6‐fold symmetric state by the interactions of the N‐terminal ≈ 1–335 residues and that the removal of this region allows the association domain to convert into a more stable 7‐fold symmetric form.

Homo-oligomerization and Activation of AMP-activated Protein Kinase Are Mediated by the Kinase Domain αG-Helix

“…The formation of large homo-oligomers is another frequent intracellular mechanism, occurring among others within the kinase family, e.g. calmodulin-dependent protein kinase 2 (CaMK2) forms dodecameric assemblies of ϳ700,000 kDa, which is believed to strongly support its functions (73,74). In AMPK, the V219E,F223E double mutation mainly affected large oligomeric complexes that were shifted to lower MM, thus indicating that additional, unknown interaction sites give rise to smaller assemblies such as dimers.…”

Structural rearrangement of CaMKIIα catalytic domains encodes activation

“…They came to this conclusion as a result of a comparative EM analysis of the intact CaMKII holoenzyme and the truncated CaMKII subunits comprising only association domains. This discrepancy regarding the stoichiometry and symmetry of the association domain core may reflect some inherent property of the holoenzyme (11). Alternatively, it may serve to reveal the difficulty of extrapolating the structure of intact proteins from the structure of isolated protein fragments.…”

“…Subsequently, the Kuriyan group (11) reported that the observed 7-fold symmetry may have arisen from the absence of the regulatory and catalytic domains. They came to this conclusion as a result of a comparative EM analysis of the intact CaMKII holoenzyme and the truncated CaMKII subunits comprising only association domains.…”

“…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.…”