Munc18-bound syntaxin readily forms SNARE complexes with synaptobrevin in native plasma membranes

TY - JOUR

T1 - Munc18-bound syntaxin readily forms SNARE complexes with synaptobrevin in native plasma membranes

AU - Zilly, Felipe E

AU - Sørensen, Jakob B

AU - Jahn, Reinhard

AU - Lang, Thorsten

N1 - Keywords: Animals; Binding Sites; Cell Membrane; Microscopy, Fluorescence; Models, Biological; Munc18 Proteins; PC12 Cells; Plasmids; Protein Binding; Qa-SNARE Proteins; R-SNARE Proteins; Rats; Recombinant Proteins; SNARE Proteins; Vesicle-Associated Membrane Protein 2

PY - 2006

Y1 - 2006

N2 - Munc18-1, a protein essential for regulated exocytosis in neurons and neuroendocrine cells, belongs to the family of Sec1/Munc18-like (SM) proteins. In vitro, Munc18-1 forms a tight complex with the SNARE syntaxin 1, in which syntaxin is stabilized in a closed conformation. Since closed syntaxin is unable to interact with its partner SNAREs SNAP-25 and synaptobrevin as required for membrane fusion, it has hitherto not been possible to reconcile binding of Munc18-1 to syntaxin 1 with its biological function. We now show that in intact and exocytosis-competent lawns of plasma membrane, Munc18-1 forms a complex with syntaxin that allows formation of SNARE complexes. Munc18-1 associated with membrane-bound syntaxin 1 can be effectively displaced by adding recombinant synaptobrevin but not syntaxin 1 or SNAP-25. Displacement requires the presence of endogenous SNAP-25 since no displacement is observed when chromaffin cell membranes from SNAP-25-deficient mice are used. We conclude that Munc18-1 allows for the formation of a complex between syntaxin and SNAP-25 that serves as an acceptor for vesicle-bound synaptobrevin and that thus represents an intermediate in the pathway towards exocytosis.

AB - Munc18-1, a protein essential for regulated exocytosis in neurons and neuroendocrine cells, belongs to the family of Sec1/Munc18-like (SM) proteins. In vitro, Munc18-1 forms a tight complex with the SNARE syntaxin 1, in which syntaxin is stabilized in a closed conformation. Since closed syntaxin is unable to interact with its partner SNAREs SNAP-25 and synaptobrevin as required for membrane fusion, it has hitherto not been possible to reconcile binding of Munc18-1 to syntaxin 1 with its biological function. We now show that in intact and exocytosis-competent lawns of plasma membrane, Munc18-1 forms a complex with syntaxin that allows formation of SNARE complexes. Munc18-1 associated with membrane-bound syntaxin 1 can be effectively displaced by adding recombinant synaptobrevin but not syntaxin 1 or SNAP-25. Displacement requires the presence of endogenous SNAP-25 since no displacement is observed when chromaffin cell membranes from SNAP-25-deficient mice are used. We conclude that Munc18-1 allows for the formation of a complex between syntaxin and SNAP-25 that serves as an acceptor for vesicle-bound synaptobrevin and that thus represents an intermediate in the pathway towards exocytosis.

U2 - 10.1371/journal.pbio.0040330

DO - 10.1371/journal.pbio.0040330

M3 - Journal article

C2 - 17002520

SN - 1544-9173

VL - 4

SP - e330

JO - PLoS Biology

JF - PLoS Biology

IS - 10

ER -