The role of the C terminus of the SNARE protein SNAP-25 in fusion pore opening and a model for fusion pore mechanics.
Formation of a fusion pore between a vesicle and its target membrane is thought to involve the so-called SNARE protein complex. However, there is no mechanistic model explaining how the fusion pore is opened by conformational changes in the SNARE complex. It has been suggested that C-terminal zipping triggers fusion pore opening. A SNAP-25 mutant named SNAP-25Delta9 (lacking the last nine C-terminal residues) should lead to a less-tight C-terminal zipping. Single exocytotic events in chromaffin cells expressing this mutant were characterized by carbon fiber amperometry and cell-attached patch capacitance measurements. Cells expressing SNAP-25Delta9 displayed smaller amperometric "foot-current" currents, reduced fusion pore conductances, and lower fusion pore expansion rates. We propose that SNARE/lipid complexes form proteolipid fusion pores. Fusion pores involving the SNAP-25Delta9 mutant will be less tightly zipped and may lead to a longer fusion pore structure, consistent with the observed decrease of fusion pore conductance.
Fang
Qinghua
Q
School of Applied and Engineering Physics, 212 Clark Hall, Cornell University, Ithaca, NY 14853, USA.
Berberian
Khajak
K
Gong
Liang-Wei
LW
Hafez
Ismail
I
Sørensen
Jakob B
JB
Lindau
Manfred
M
D000818:Animals; D020013:Calcium Signaling; D002417:Cattle; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism; D005089:Exocytosis; D007700:Kinetics; D008561:Membrane Fusion; D050825:Synaptosomal-Associated Protein 25 / Q000737:chemistry* / Q000378:metabolism*
D050825:Synaptosomal-Associated Protein 25