Combinatorial SNARE complexes with VAMP7 or VAMP8 define different late endocytic fusion events.
Both heterotypic and homotypic fusion events are required to deliver endocytosed macromolecules to lysosomes and remodel late endocytic organelles. A trans-SNARE complex consisting of Q-SNAREs syntaxin 7, Vti1b and syntaxin 8 and the R-SNARE VAMP8 has been shown by others to be responsible for homotypic fusion of late endosomes. Using antibody inhibition experiments in rat liver cell-free systems, we confirmed this result, but found that the same Q-SNAREs can combine with an alternative R-SNARE, namely VAMP7, for heterotypic fusion between late endosomes and lysosomes. Co-immunoprecipitation demonstrated separate syntaxin 7 complexes with either VAMP7 or VAMP8 in solubilized rat liver membranes. Additionally, overexpression of the N-terminal domain of VAMP7, in cultured fibroblastic cells, inhibited the mixing of a preloaded lysosomal content marker with a marker delivered to late endosomes. These data show that combinatorial interactions of SNAREs determine whether late endosomes undergo homotypic or heterotypic fusion events.
Pryor
Paul R
PR
Cambridge Institute for Medical Research and Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, UK.
Mullock
Barbara M
BM
Bright
Nicholas A
NA
Lindsay
Margaret R
MR
Gray
Sally R
SR
Richardson
Simon C W
SC
Stewart
Abigail
A
James
David E
DE
Piper
Robert C
RC
Luzio
J Paul
JP
D000818:Animals; D002474:Cell-Free System / Q000276:immunology / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000276:immunology / Q000378:metabolism; D047468:Immunoprecipitation; D008247:Lysosomes / Q000276:immunology / Q000378:metabolism; D008561:Membrane Fusion; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D016716:PC12 Cells; D021381:Protein Transport / Q000502:physiology; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D051381:Rats; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins / Q000276:immunology / Q000378:metabolism*
D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; C496926:Vamp7 protein, rat; C491830:Vamp8 protein, rat; D033921:Vesicular Transport Proteins