Identification of domains essential for the assembly of calcium/calmodulin-dependent protein kinase II holoenzymes

Abstract

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II), as isolated from brain, is a multimeric complex composed predominantly of two subunits, a and β, products of unique genes. Little is known about how subunit composition influences holoenzyme structure or how the domain(s) of each subunit interact to form holoenzymes. We show here that holoenzymes composed of only α or only β subunits exhibit different biophysical properties. The S values of a and β are 17.2 and 14.5 S while the Stokes's radii are 85 and 111 Å, respectively, indicating their structures are different. C-terminal truncations of the α subunit show that amino acids 382478 are necessary for holoenzyme formation and that amino acids 427-478 contribute to holoenzyme stability. Additionally, the C-terminal domains of both the α subunit, α315-478, and β subunit, β314-542, formed oligomers indicating the sufficiency of the C-terminal domain for multimer formation. Using the yeast two-hybrid system we show, in vivo, that full-length subunits, α1-478 and β1-542, interact with themselves or each other interchangeably. Additionally, the C-terminal domains of the α subunit, α315-478 and β subunit, β314-542 associated with themselves in a manner indistinguishable from their association with full-length α or subunits. Further studies revealed that the C-terminal domains of the a and β subunits contain information necessary for interaction with β but not α. These data are summarized into a model describing the assembly of CaM kinase H holoenzymes.