Ca2+-induced recruitment of the secretory vesicle protein DOC2B to the target membrane

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Ca2+-induced recruitment of the secretory vesicle protein DOC2B to the target membrane

Ca2+-dependent fusion of transport vesicles at their target can be enhanced by intracellular Ca2+ and diacylglycerol. Diacylglycerol induces translocation of the vesicle priming factor Munc13 and association of the secretory vesicle protein DOC2B to the membrane. Here we demonstrate that a rise in intracellular Ca2+ is sufficient for a Munc13-independent recruitment of DOC2B to the target membrane. This novel mechanism occurred readily in the absence of Munc13 and was not influenced by DOC2B mutations that abolish Munc13 binding. Purified DOC2B (expressed as a bacterial fusion protein) bound phospholipids in a Ca2+-dependent way, suggesting that the translocation is the result of a C2 domain activation mechanism. Ca 2+-induced translocation was also observed in cultured neurons expressing DOC2B-enhanced green fluorescent protein. In this case, however, various degrees of membrane association occurred under resting conditions, suggesting that physiological Ca2+ concentrations modulate DOC2B localization. Depolarization of the neurons induced a complete translocation of DOC2B-enhanced green fluorescent protein to the target membrane within 5 s. We hypothesize that this novel Ca2+-induced activity of DOC2B functions synergistically with diacylglycerol-induced Munc13 binding to enhance exocytosis during episodes of high secretory activity

Doc2 isoforms play dual roles in insulin secretion and insulin-stimulated glucose uptake

Aims/hypothesis Glucose-stimulated insulin secretion (GSIS) and insulin-stimulated glucose uptake are processes that rely on regulated intracellular vesicle transport and vesicle fusion with the plasma membrane. DOC2A and DOC2B are calcium-sensitive proteins that were identified as key components of vesicle exocytosis in neurons. Our aim was to investigate the role of DOC2 isoforms in glucose homeostasis, insulin secretion and insulin action. Methods DOC2 expression was measured by RT-PCR and western blotting. Body weight, glucose tolerance, insulin action and GSIS were assessed in wild-type (WT), Doc2

Paroxysmal kinesigenic dyskinesia: Cortical or non-cortical origin

AbstractParoxysmal kinesigenic dyskinesia (PKD) is characterized by involuntary dystonia and/or chorea triggered by a sudden movement. Cases are usually familial with an autosomal dominant inheritance. Hypotheses regarding the pathogenesis of PKD focus on the controversy whether PKD has a cortical or non-cortical origin. A combined familial trait of PKD and benign familial infantile seizures has been reported as the infantile convulsions and paroxysmal choreoathetosis (ICCA) syndrome. Here, we report a family diagnosed with ICCA syndrome with an Arg217STOP mutation. The index patient showed interictal EEG focal changes compatible with paroxysmal dystonic movements of his contralateral leg. This might support cortical involvement in PKD