SNAREs are concentrated in cholesterol-dependent clusters that define docking and fusion sites for exocytosis.
During exocytosis, SNARE proteins of secretory vesicles interact with the corresponding SNARE proteins in the plasmalemma to initiate the fusion reaction. However, it is unknown whether SNAREs are uniformly distributed in the membrane or whether specialized fusion sites exist. Here we report that in the plasmalemma, syntaxins are concentrated in 200 nm large, cholesterol-dependent clusters at which secretory vesicles preferentially dock and fuse. The syntaxin clusters are distinct from cholesterol-dependent membrane rafts since they are Triton X-100-soluble and do not co-patch with raft markers. Synaptosomal-associated protein (SNAP)-25 is also clustered in spots, which partially overlap with syntaxin. Cholesterol depletion causes dispersion of these clusters, which is associated with a strong reduction in the rate of secretion, whereas the characteristics of individual exocytic events are unchanged. This suggests that high local concentrations of SNAREs are required for efficient fusion.
Lang
T
T
Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
Bruns
D
D
Wenzel
D
D
Riedel
D
D
Holroyd
P
P
Thiele
C
C
Jahn
R
R
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003505:Cyclodextrins / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D008561:Membrane Fusion / Q000502:physiology*; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism*; D008567:Membranes, Artificial; D009419:Nerve Tissue Proteins / Q000378:metabolism; D050765:Qa-SNARE Proteins; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D050600:SNARE Proteins; D022142:Secretory Vesicles / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins; D047392:beta-Cyclodextrins
D003505:Cyclodextrins; D008565:Membrane Proteins; D008567:Membranes, Artificial; D009419:Nerve Tissue Proteins; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins; D050600:SNARE Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol