Syntaxin 7 is localized to late endosome compartments, associates with Vamp 8, and Is required for late endosome-lysosome fusion.
Protein traffic from the cell surface or the trans-Golgi network reaches the lysosome via a series of endosomal compartments. One of the last steps in the endocytic pathway is the fusion of late endosomes with lysosomes. This process has been reconstituted in vitro and has been shown to require NSF, alpha and gamma SNAP, and a Rab GTPase based on inhibition by Rab GDI. In Saccharomyces cerevisiae, fusion events to the lysosome-like vacuole are mediated by the syntaxin protein Vam3p, which is localized to the vacuolar membrane. In an effort to identify the molecular machinery that controls fusion events to the lysosome, we searched for mammalian homologues of Vam3p. One such candidate is syntaxin 7. Here we show that syntaxin 7 is concentrated in late endosomes and lysosomes. Coimmunoprecipitation experiments show that syntaxin 7 is associated with the endosomal v-SNARE Vamp 8, which partially colocalizes with syntaxin 7. Importantly, we show that syntaxin 7 is specifically required for the fusion of late endosomes with lysosomes in vitro, resulting in a hybrid organelle. Together, these data identify a SNARE complex that functions in the late endocytic system of animal cells.
Mullock
B M
BM
Wellcome Trust Centre for Molecular Mechanisms in Disease, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 2XY, United Kingdom.
Smith
C W
CW
Ihrke
G
G
Bright
N A
NA
Lindsay
M
M
Parkinson
E J
EJ
Brooks
D A
DA
Parton
R G
RG
James
D E
DE
Luzio
J P
JP
Piper
R C
RC
D000818:Animals; D002460:Cell Line; D004285:Dogs; D004705:Endocytosis; D011992:Endosomes / Q000502:physiology* / Q000648:ultrastructure; D004847:Epithelial Cells / Q000502:physiology / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000502:physiology / Q000648:ultrastructure; D007668:Kidney / Q000502:physiology / Q000648:ultrastructure; D008099:Liver / Q000502:physiology / Q000648:ultrastructure; D008247:Lysosomes / Q000502:physiology* / Q000648:ultrastructure; D008561:Membrane Fusion / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000502:physiology / Q000648:ultrastructure; D021601:trans-Golgi Network / Q000502:physiology / Q000648:ultrastructure
D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; C491830:Vamp8 protein, rat