Promiscuous interaction of SNAP-25 with all plasma membrane syntaxins in a neuroendocrine cell.
SNAP-25 (25 kDa synaptosome-associated protein) is found in cells that release neurotransmitters and hormones, and plays a central role in the fusion of secretory vesicles with the plasma membrane. SNAP-25 has been shown to interact specifically with syntaxin 1, a 35 kDa membrane protein, to mediate the fusion process. Here, we investigated whether other known syntaxin isoforms found at the plasma membrane can serve as binding partners for SNAP-25 in vivo. In our analysis, we employed rat phaeochromocytoma PC12 cells that are often used as a model of neuronal functions. We now show that these cells contain large amounts of SNAP-25, which interacts not only with syntaxin 1, but also with ubiquitous syntaxins 2, 3 and 4. The plasma membrane syntaxins appear to occupy complementary domains at the plasma membrane. In defined reactions, the ubiquitous plasma membrane syntaxin isoforms, when in binary complexes with SNAP-25, readily bound vesicular synaptobrevin to form SDS-resistant SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) complexes implicated in membrane fusion. However, vesicular synaptotagmin and cytosolic complexin, both implicated in the fusion process, exhibited differential ability to interact with the SNARE complexes formed by syntaxins 1-4, suggesting that the plasma membrane syntaxins may mediate vesicle fusion events with different properties.
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
Mark
M
Bajohrs
Frédéric
F
Darios
Sew-Yeu
SY
Peak-Chew
Bazbek
B
Davletov
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism*; D016716:PC12 Cells; D011485:Protein Binding; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000378:metabolism*; D051381:Rats; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism*; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism
D050765:Qa-SNARE Proteins; C498858:Snap23 protein, rat; D050825:Synaptosomal-Associated Protein 25; C494706:Vamp2 protein, rat; D050988:Vesicle-Associated Membrane Protein 2; D033921:Vesicular Transport Proteins