In vitro modulation of protein kinase CK2-mediated phosphorylation of the neuronal growth-associated protein B-50 (GAP-43)

The presynaptic protein B-50 (GAP-43) is a protein kinase CK2 (CK2) substrate phosphorylated in vitro in a polylysine-dependent manner. Polylysine was compared to other basic compounds to further define characteristics of this phosphorylation. Total histone stimulated CK2 to a similar extent, but at higher concentrations than did polylysine, while spermine was without effect. Histone H2A accounted for the stimulatory effect of the mixed histone. Correlation between CK2 activity and the length of polylysine was observed. Polylysine-dependent B-50 phosphorylation was observed with both recombinant human CK2 and purified rat brain CK2. Serine/threonine phosphorylation occurred on the fragment, B-50_1.132, and serine phosphorylation on B-50 _133-226. Phosphorylation of B-50 by CK2 was inhibited by actin and calmodulin. These results suggest that local interactions between CK2, basic proteins and/or actin at the neuronal membrane and calmodulin binding may determine the phosphorylated state of B-50 at CK2 sites.