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.

Files

Additional details