Mutations in the drosophila Rop gene suggest a function in general secretion and synaptic transmission

Association of Drosophila cysteine string proteins with membranes

“…Thus, all Dcsp's was found to be membrane-bound. Unlike our findings with the protein Rop (a sec-1 homologue in yeast), none of the Dcsp's was recovered at the top of the gradient as soluble protein [3,11]. When subcellular fractionation was performed in Torpedo electric organ a considerable fraction of the Dcsp was recovered as soluble material [5,6].…”

Supramaximal cholecystokinin displaces Munc18c from the pancreatic acinar basal surface, redirecting apical exocytosis to the basal membrane

“…It is now known that Munc18a does not simply act as a negative regulator that restricts the synaptic vesicle from exocytotic fusion; rather, its dissociation from syntaxin-1A changes syntaxin-1A from a "closed" to an "open" configuration capable of binding its cognate SNARE proteins (52). This would explain the previous studies suggesting that Munc18a possesses apparently conflicting positive and negative roles in exocytosis (14,53,54). Moreover, Munc18a not only plays this complex role in SNARE complex assembly but, as was recently shown, plays a role in the control of fusion pore dynamics as well (55).…”

Doc2 is not associated with known regulated exocytotic or endosomal compartments in adrenal chromaffin cells

“…We have previously shown that, in order to shift the distribution of chromaffin-granule membranes, the organelles in a large-granule fraction can be lysed ; the granule membranes are then distributed in markedly less dense fractions when run on a 0.3-1.2 M sucrose gradient [17]. Following this procedure, granule membranes, indicated by the presence of DβH and synaptophysin ( Figures 3A and 3B), were found in less dense fractions than expected for intact granules, and were clearly separated from membranes containing Doc2, which remained in the denser fractions (9)(10)(11)(12)(13)(14) on this gradient (Figures 3A and 3B). There was little evidence for any intact granules remaining on the gradient, as little or no synaptophysin (an integral membrane component of SLMVs and chromaffin granules) was detected in fractions 12-14.…”

“…Doc2 contains two C2 domains, which are likely to allow its Ca# + -dependent binding to phospholipids [7], and it has been implicated in regulated exocytosis as a result of its ability to bind munc-18 (nsec-1) [8] and munc-13 [9]. These two proteins are known to have a key function in neurotransmitter release, based on molecular genetic evidence [10,11]. In addition, overexpression of Doc2 increased the release of co-transfected growth hormone (as a marker of secretory granule contents) from neuroendocrine PC12 cells, and cotransfection with N-or C-terminal fragments of Doc2 was inhibitory [12].…”