Rec Packet Week 3

Rec Packet Week 3 - Vocabulary Chelator Endosome Lysosome...

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Vocabulary Chelator Endosome Lysosome Lumen Anterograde Retrograde Antagonist Agonist Cisternae Nascent
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EMBO reports VOL 8 | NO 3 | 2007 ©2007 EUROPEAN MOLECULAR BIOLOGY ORGANIZATION review review 236 Calcium: a fundamental regulator of intracellular membrane fusion? Jesse C. Hay University of Montana, Missoula, Montana, USA For many years, it has been known that an increase in cytosolic calcium triggers the fusion of secretory granules and synaptic vesicles with the plasma membrane. However, the role of calcium in the intracellular membrane-fusion reactions that coordinate the secretory and endocytic pathways has been less clear. Initially, there was accumulating evidence to indicate that a focally localized and transient calcium signal is required to trig- ger even those fusion events formerly classified as ‘constitutive’— that is, those that normally occur in the absence of global cytoso- lic calcium increases. Therefore, calcium seemed to be a required fundamental co-factor underlying all biological membrane-fusion steps, perhaps with a conserved mechanism of action. However, although such unification would be gratifying, new data indicate that several intracellular fusion events do not require calcium after all. In this review, the evidence for calcium requirements and its modes of action in constitutive trafficking are discussed. As a challenging perspective, I suggest that the specific absence of calcium requirements for some transport steps in fact expands the function of calcium in trafficking, because divergent luminal calcium concentrations and requirements for fusion might increase the specificity with which intracellular membrane-fusion partners are determined. Keywords: calcium; membrane fusion; secretion; SNARE; vesicle transport EMBO reports (2007) 8, 236–240. doi:10.1038/sj.embor.7400921 Introduction Vesicle targeting and fusion in the endomembrane system are mediated by several conserved protein families. Those that are rel- evant to this review are the vesicle coat–protein complexes, such as COPI and COPII, which select cargo and catalyse the budding of transport vesicles with specific compositions and destinations. Rab GTPases coordinate tethering interactions between vesicles and target membranes, and activate the fusion machinery. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are integral membrane proteins that bridge the opposing membranes and mediate their fusion. Calcium is required in constitutive membrane trafficking The first indications that calcium is required for constitutive secre- tion came from studies of trafficking from the endoplasmic reticulum was shown to be required for early endosome fusion (Colombo et al , In these cases, fusion was inhibited by the fast calcium chelator 1,2-
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This note was uploaded on 04/07/2008 for the course BIOSCI 0150 taught by Professor Dr.roberts during the Spring '08 term at Pittsburgh.

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Rec Packet Week 3 - Vocabulary Chelator Endosome Lysosome...

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