title: Complexins: small but capable.
abstract: Despite intensive research, it is still unclear how an immediate and profound acceleration of exocytosis is triggered by appropriate Ca(2+)-stimuli in presynaptic terminals. This is due to the fact that the molecular mechanisms of "docking" and "priming" reactions, which set up secretory vesicles to fuse at millisecond time scale, are extremely hard to study. Yet, driven by a fruitful combination of in vitro and in vivo analyses, our mechanistic understanding of Ca(2+)-triggered vesicle fusion has certainly advanced in the past few years. In this review, we aim to highlight recent progress and emerging views on the molecular mechanisms, by which constitutively forming SNAREpins are organized in functional, tightly regulated units for synchronized release. In particular, we will focus on the role of the small regulatory factor complexin whose function in Ca(2+)-dependent exocytosis has been controversially discussed for more than a decade. Special emphasis will also be laid on the functional relationship of complexin and synaptotagmin, as both proteins possibly act as allies and/or antagonists to govern SNARE-mediated exocytosis.
authors.affiliation: Zentrum für Human- und Molekularbiologie, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany. ralf.mohrmann@uks.eu.|Medical Faculty, Department of Physiology, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany. ralf.mohrmann@uks.eu.
authors.forename: Ralf
authors.initials: R
authors.lastname: Mohrmann
authors.affiliation: Medical Faculty, Department of Physiology, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany.
authors.forename: Madhurima
authors.initials: M
authors.lastname: Dhara
authors.affiliation: Medical Faculty, Department of Physiology, University of Saarland, CIPMM, 66421, Homburg/Saar, Germany. dieter.bruns@uks.eu.
authors.forename: Dieter
authors.initials: D
authors.lastname: Bruns
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D005089:Exocytosis; D006801:Humans; D008561:Membrane Fusion; D008954:Models, Biological; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011485:Protein Binding; D050600:SNARE Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism*; D050857:Synaptotagmins / Q000378:metabolism
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; C095992:complexin I; D050857:Synaptotagmins; D002118:Calcium
keywords: Ca2+ triggered exocytosis; Complexin; Membrane fusion; SNARE regulators; Synaptotagmin