title: Synaptotagmin-mediated bending of the target membrane is a critical step in Ca(2+)-regulated fusion.
abstract: Decades ago it was proposed that exocytosis involves invagination of the target membrane, resulting in a highly localized site of contact between the bilayers destined to fuse. The vesicle protein synaptotagmin-I (syt) bends membranes in response to Ca(2+), but whether this drives localized invagination of the target membrane to accelerate fusion has not been determined. Previous studies relied on reconstituted vesicles that were already highly curved and used mutations in syt that were not selective for membrane-bending activity. Here, we directly address this question by utilizing vesicles with different degrees of curvature. A tubulation-defective syt mutant was able to promote fusion between highly curved SNARE-bearing liposomes but exhibited a marked loss of activity when the membranes were relatively flat. Moreover, bending of flat membranes by adding an N-BAR domain rescued the function of the tubulation-deficient syt mutant. Hence, syt-mediated membrane bending is a critical step in membrane fusion.
authors.affiliation: Howard Hughes Medical Institute, USA.
authors.forename: Enfu
authors.initials: E
authors.lastname: Hui
authors.forename: Colin P
authors.initials: CP
authors.lastname: Johnson
authors.forename: Jun
authors.initials: J
authors.lastname: Yao
authors.forename: F Mark
authors.initials: FM
authors.lastname: Dunning
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Chapman
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D005089:Exocytosis; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D009154:Mutation; D050600:SNARE Proteins / Q000378:metabolism; D050857:Synaptotagmins / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008081:Liposomes; D050600:SNARE Proteins; D050857:Synaptotagmins; D002118:Calcium
references.citation: Cell. 1995 Mar 24;80(6):929-38
references.pmid: 7697723
references.citation: Nat Struct Mol Biol. 2006 Apr;13(4):323-30
references.pmid: 16565726
references.citation: J Am Chem Soc. 2003 Dec 10;125(49):15233-42
references.pmid: 14653758
references.citation: Neuron. 1991 Mar;6(3):411-20
references.pmid: 1825782
references.citation: Biophys J. 2007 May 15;92(10):3595-602
references.pmid: 17325001
references.citation: Biochim Biophys Acta. 2006 Mar;1761(3):313-23
references.pmid: 16627002
references.citation: Science. 2004 Apr 9;304(5668):289-92
references.pmid: 15016962
references.citation: Nat Struct Mol Biol. 2007 Oct;14(10):904-11
references.pmid: 17891149
references.citation: EMBO J. 2006 Jun 21;25(12):2898-910
references.pmid: 16763559
references.citation: Neuron. 1999 Oct;24(2):363-76
references.pmid: 10571230
references.citation: Science. 2004 Apr 16;304(5669):435-8
references.pmid: 15044754
references.citation: Cell. 1998 Mar 20;92(6):759-72
references.pmid: 9529252
references.citation: Nat Struct Mol Biol. 2004 Jan;11(1):36-44
references.pmid: 14718921
references.citation: J Biol Chem. 2008 Nov 14;283(46):31763-75
references.pmid: 18784080
references.citation: Biochemistry. 1994 Aug 16;33(32):9477-88
references.pmid: 8068622
references.citation: Nature. 2002 Jul 18;418(6895):340-4
references.pmid: 12110842
references.citation: Curr Opin Cell Biol. 2003 Aug;15(4):372-81
references.pmid: 12892776
references.citation: J Biol Chem. 1998 May 29;273(22):13995-4001
references.pmid: 9593749
references.citation: Neuron. 2001 Dec 20;32(6):1057-69
references.pmid: 11754837
references.citation: Biophys J. 2002 Jun;82(6):3072-80
references.pmid: 12023230
references.citation: Annu Rev Biochem. 2003;72:175-207
references.pmid: 14527322
references.citation: Annu Rev Biochem. 2008;77:615-41
references.pmid: 18275379
references.citation: Biochemistry. 2006 Oct 31;45(43):12917-28
references.pmid: 17059209
references.citation: Mol Biol Cell. 2005 Oct;16(10):4755-64
references.pmid: 16093350
references.citation: BMC Genomics. 2004 Jul 06;5(1):43
references.pmid: 15238157
references.citation: Proc Natl Acad Sci U S A. 2002 Feb 5;99(3):1665-70
references.pmid: 11805296
references.citation: Nat Struct Mol Biol. 2006 Mar;13(3):209-17
references.pmid: 16491093
references.citation: J Cell Biol. 2002 Jul 22;158(2):273-82
references.pmid: 12119360
references.citation: J Neurosci. 2004 Sep 29;24(39):8542-50
references.pmid: 15456828
references.citation: Mol Biol Cell. 2008 Dec;19(12):5093-103
references.pmid: 18799625
references.citation: Traffic. 2002 Apr;3(4):256-67
references.pmid: 11929607
references.citation: Science. 2007 May 25;316(5828):1205-8
references.pmid: 17478680
references.citation: Proc Natl Acad Sci U S A. 2003 Feb 18;100(4):2082-7
references.pmid: 12578982
references.citation: Neuron. 1994 Apr;12(4):707-16
references.pmid: 7909233
references.citation: Biochemistry. 1998 Nov 17;37(46):16106-15
references.pmid: 9819203
references.citation: Nat Struct Mol Biol. 2008 Aug;15(8):827-35
references.pmid: 18622390
references.citation: J Cell Biol. 2001 Oct 15;155(2):193-200
references.pmid: 11604418