Oligomeric structure of alpha-calmodulin-dependent protein kinase II

The subunit stoichiometry and symmetry of the neuronal alpha -calmodulin-de pendent protein kinase II (alpha CaMKII) is investigated in this report to understand the structural basis of its regulation and mechanism at the mole cular level. Two preparations are studied, alpha CaMKII obtained by overexp ression in baculovirus-transfected insect cells and CaMKII isolated from ra t forebrain. The structures, are studied by electron microscopy and image a nalysis. Single-particle analysis of individual molecular images reveals a molecule with a circular outline and pronounced 6-fold rotational symmetry of the central part. The central part has an outer radius of similar to6 nm and is composed of six lobes grouped around a hollow centre. The outer rin g extends to similar to 15 nm and consists of 12 apparent domains. These data are interpreted in terms of a three-dimensional model of the alp ha CaMKII complex consisting of 12 subunits, each corresponding to a single alpha CaMKII polypeptide chain. The inner ring corresponding to approximat ely one-third of the molecular mass of the complex is made up of the C-term inal association domains. The 12 association domains are arranged in two co ncentric hexagonal rings at different axial levels and in rotational regist er. The outer ring corresponding to the remaining molecular mass of the com plex is made up of the 12 N-terminal catalytic domains located at an axial level halfway between the two levels of the association domains. The 6-fold symmetry of stacked association domains may derive from subunit arrangemen ts corresponding to either the C6 or the D6 point group symmetries. The sym metry and the resulting subunit arrangement define the pattern and extent o f regulatory autophosphorylation within the aCaMKII complex. (C) 2001 Acade mic Press.