Palmitoylation sites and processing of synaptotagmin I, the putative calcium sensor for neurosecretion.

Synaptotagmin I, the calcium sensor for neurotransmission, is palmitoylated. We have identified the palmitoylation sites as five cysteine residues located between the transmembrane and cytoplasmic regions. In contrast to wild-type synaptotagmin, the non-acylated mutant is not converted to the endoglycosidase-H-resistant form after expression in CV-1 cells. This indicates a block in transport through the Golgi complex. However, when expressed in PC-12 and RBL cells non-acylated synaptotagmin is targeted to the plasma membrane and to secretory granules. No significant cleavage of [(3)H]palmitate from synaptotagmin was observed in pulse-chase experiments. This indicates that the majority of fatty acids are structural rather than dynamic components.