Interaction of Ganglioside with Specific Peptide Sequences as a Mechanism for the Modulation of Calmodulin-Dependent Enzymes

Abstract

We examined the interaction between gangliosides and synthetic peptides of calmodulin (CaM)-dependent enzymes to confirm the hypothesis that interaction between gangliosides and the CaM-like site (CLS) of the enzyme is a mechanism for the modulation of the enzyme activity by gangliosides. Gangliosides, GD1b, GT1b, and GD1a, inhibited the activity of CaM-independently activated cAMP-phosphodiesterase and their inhibition was cancelled by a peptide consisting of 17 amino acid residues of a plasma membrane Ca(2+)-pump CLS, suggesting the involvement of the interaction between the peptide and the gangliosides. The peptide of an assumed CLS of phosphodiesterase also cancelled the inhibition. On the other hand, the gangliosides interacted with synthetic CaM-binding site (CBS) peptides of phosphodiesterase, calcineurin, Ca(2+)-pump, and Ca2+/calmodulin-dependent protein kinase II. Moreover, gangliosides GM3 and LM1, that activate but do not inhibit phosphodiesterase, interacted with the CBS peptides, whereas they did not bind to CLS peptides. On the basis of these new findings, we propose a revised model for the ganglioside-mediated modulation of CaM-dependent enzymes, i.e. without CaM, gangliosides bind to CBS and thus stimulate the enzyme activity, acting like CaM. At higher concentrations, they bind to CLS of the enzymes as well and inhibit the activity, acting like the CBS of the enzyme.