In the late endocytic pathway, it has been proposed that endocytosed macromolecules are delivered to a proteolytic environment by 'kiss-and-run' events or direct fusion between late endosomes and lysosomes. To test whether the fusion hypothesis accounts for delivery to lysosomes in living cells, we have used confocal microscopy to examine content mixing between lysosomes loaded with rhodamine-dextran and endosomes subsequently loaded with Oregon-Green-dextran. Both kissing and explosive fusion events were recorded. Data from cell-free content-mixing assays have suggested that fusion is initiated by tethering, which leads to formation of a trans-SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) protein complex and then release of lumenal Ca2+, followed by membrane bilayer fusion. We have shown that the R-SNARE (arginine-containing SNARE) protein VAMP (vesicle-associated membrane protein) 7 is necessary for heterotypic fusion between late endosomes and lysosomes, whereas a different R-SNARE, VAMP 8 is required for homotypic fusion of late endosomes. After fusion of lysosomes with late endosomes, lysosomes are re-formed from the resultant hybrid organelles, a process requiring condensation of content and the removal/recycling of some membrane proteins.
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January 2005
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Review Article|
January 01 2005
Membrane traffic to and from lysosomes.
J. Paul Luzio
;
J. Paul Luzio
1
*Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, U.K.
†Department of Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, U.S.A.
1To whom correspondence should be addressed (email jpl10@cam.ac.uk).
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Paul R. Pryor
;
Paul R. Pryor
*Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, U.K.
†Department of Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, U.S.A.
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Sally R. Gray
;
Sally R. Gray
*Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, U.K.
†Department of Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, U.S.A.
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Matthew J. Gratian
;
Matthew J. Gratian
*Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, U.K.
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Robert C. Piper
;
Robert C. Piper
†Department of Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, U.S.A.
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Nicholas A. Bright
Nicholas A. Bright
*Cambridge Institute for Medical Research, University of Cambridge, Wellcome Trust/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, U.K.
†Department of Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, U.S.A.
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Biochem Soc Symp (2005) 72: 77–86.
Citation
Jeff McIlhinney, Nigel Hooper, J. Paul Luzio, Paul R. Pryor, Sally R. Gray, Matthew J. Gratian, Robert C. Piper, Nicholas A. Bright; Membrane traffic to and from lysosomes.. Biochem Soc Symp 1 January 2005; 72 77–86. doi: https://doi.org/10.1042/bss0720077
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