BIOCHEMICAL AND FUNCTIONAL-CHARACTERIZATION OF THE SYNAPTIC VESICLE-ASSOCIATED FORM OF CA2+ CALMODULIN-DEPENDENT PROTEIN-KINASE-II/

Ca2+/calmodulin-dependent protein kinase II (CaMPKII) is a brain-enric hed protein kinase that plays important roles in synaptic transmission and plasticity. In nerve terminals, a form of CaMPKII is associated w ith synaptic vesicles and binds the COOH-terminal region of synapsin I (SYNI). The biochemical properties of the vesicle-associated form of CaMPKII have been investigated and compared with those of the soluble forebrain enzyme Both the alpha- and beta-subunits of CaMPKII copurify ing with synaptic vesicles were tightly associated with the vesicle me mbrane. The vesicle-associated form of CaMPKII was indistinguishable f rom the soluble form with respect to sites of autophosphorylation, kin etics of both autophosphorylation and SYNI phosphorylation, and induct ion of autonomous activity upon autophosphorylation. Although both sub units of the soluble CaMPKII interacted with a photoactivatable SYNI d erivative, only the alpha-subunit of the synaptic vesicle-associated C aMPKII bound to the COOH-terminal region of SYNI. The latter interacti on was strongly dependent on the phosphorylation state of SYNI and on divalent cations, but appeared to be independent of autophosphorylatio n. These results demonstrate that, although the vesicle-associated for m of CaMPKII is catalytically indistinguishable from the soluble form, it exhibits distinct characteristics concerning its association with the vesicle membrane and with SYNI.