Author/Editor		Jorgačevski, Jernej; Potokar, Maja; Grilc, Sonja; Kreft, Marko; Liu, Wei; Barclay, Jeff W; Bueckers, Johanna; Medda, Rebecca; Hell, Stefan W; Parpura, Vladimir; Burgoyne, Robert D; Zorec, Robert
Title		Munc 18-1 tuning of vesicle merger and fusion pore properties
Type		članek
Source		J Neurosci
Vol. and No.		Letnik 31, št. 24
Publication year		2011
Volume		str. 9055-66
Language		eng
Abstract		The release ofhormones and neurotransmitters, mediated by regulated exocytosis, can be modified by regulation of the fusion pore. The fusion pore is considered stable and narrow initially, eventually leading to the complete merger of the vesicle and the plasma membranes. By using the high- resolution patch -clamp capacitance technique, we studied single vesicles and asked whether the Secl/Muncl8 proteins, interacting with the membrane fusion-mediating SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, affect fusion pore properties. Muncl8-1 mutants we re transfected into lactotrophs to affect the interaction of Muncl8-1 with syntaxinl (Synt1) (R39C), Rab3A (E466K), and Mints (P242S). Compared with wild-type, Muncl8-1 E466K increased the frequency ofthe fusion event. The latter two mutants increased the fusion pore dwell-time. All the mutants stabilized narrow fusion pores and increased the amplitude of fusion events, likely via preferential fusion oflarger vesicIes, since overexpression of Munc18-1 R39C did not affect the ave rage size of vesicIes, as determined by stimulated emission depletion (STED) microscopy. Single-molecule atomic force microscopy experiments revealed that wild-type Munc18-1, but not Munc18-1 R39C, abrogates the interaction between synaptobrevin2 (Syb2) and Synt1 binary trans-complexes. However, neither form ofMuncl8-1 affected the interaction ofSyb2 with the preformed binary cis-Synt1ASNAP25B complexes. This indicates that Munc18-1 performs a proofing function by inhibiting tethering of Syb2-containing ves ici es solely to Synt1 at the plasmalemma and favoring vesicular tethering to the preformed binary cis-complex of Synt1A-SNAP25B. The association of Muncl8-1 with the ternary SNARE complex leads to tuning of fusion pores via multiple and converging mechanisms involving Muncl8-1 interactions with Synt1A, Rab3A, and Mints.
Descriptors		PITUITARY GLAND EXOCYTOSIS PATCH-CLAMP TECHNIQUES MICROSCOPY, ATOMIC FORCE IMMUNOHISTOCHEMISTRY RATS, WISTAR PLASMIDS MICROSCOPY, CONFOCAL TRANSFECTION CELLS, CULTURED