Ganglioside GM1 modulation of calcium/calmodulin-dependent protein kinase II activity and autophosphorylation

Abstract

Purified Ca 2+/calmodulin-dependent protein kinase II (CaM kinase II) is functionally modulated by physiological concentrations of gangliosides. Ganglioside GM1 has a dual effect on the Ca 2+/calmodulin-dependent and independent activity and autophosphorylation of CaM kinase II. In the absence of Ca 2+ and calmodulin (CaM), GM1 stimulates the autophosphorylation of the kinase and its activity evaluated using synapsin I as a substrate. This effect was maximal at 5–10 μM GM1, independent of the presence of Ca 2+ and relatively resistant to the inhibition by phenothiazines. The stimulation of the autophosphorylation involved predominantly the β-β′ subunit of the kinase. In contrast, in the presence of Ca 2+/CaM stimulation, ganglioside GM1 caused a dose-dependent inhibition of the catalytic activity and autophosphorylation to values observed in the presence of gangliosides without Ca 2+/CaM. This inhibition ( K i = 40–45 μM) was non-competitive with respect to CaM and effective on both subunits of CaM kinase II. The lack of additive inhibition in the presence of trifluoperazine suggests that GM1 interferes with the CaM binding site of CaM kinase II. Gangliosides, by inducing a blockade of the action of CaM and a simultaneous CaM-independent stimulation of CaM kinase II may represent a novel class of biological regulators of CaM-dependent enzymes.