The carboxy-terminal domain of complexin I stimulates liposome fusion.
Regulated exocytosis requires tight coupling of the membrane fusion machinery to a triggering signal and a fast response time. Complexins are part of this regulation and, together with synaptotagmins, control calcium-dependent exocytosis. Stimulatory and inhibitory functions have been reported for complexins. To test if complexins directly affect membrane fusion, we analyzed the 4 known mammalian complexin isoforms in a reconstituted fusion assay. In contrast to complexin III (CpxIII) and CpxIV, CpxI and CpxII stimulated soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-pin assembly and membrane fusion. This stimulatory effect required a preincubation at low temperature and was specific for neuronal t-SNAREs. Stimulation of membrane fusion was lost when the carboxy-terminal domain of CpxI was deleted or serine 115, a putative phosphorylation site, was mutated. Transfer of the carboxy-terminal domain of CpxI to CpxIII resulted in a stimulatory CpxIII-I chimera. Thus, the carboxy-terminal domains of CpxI and CpxII promote the fusion of high-curvature liposomes.
Malsam
Jörg
J
Heidelberg University Biochemistry Center, 69120 Heidelberg, Germany.
Seiler
Florian
F
Schollmeier
Yvette
Y
Rusu
Patricia
P
Krause
Jean Michel
JM
Söllner
Thomas H
TH
D033942:Adaptor Proteins, Vesicular Transport; D000595:Amino Acid Sequence; D008081:Liposomes / Q000737:chemistry; D008561:Membrane Fusion; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D050600:SNARE Proteins / Q000494:pharmacology; D050988:Vesicle-Associated Membrane Protein 2 / Q000494:pharmacology
D033942:Adaptor Proteins, Vesicular Transport; D008081:Liposomes; D009419:Nerve Tissue Proteins; D050600:SNARE Proteins; D050988:Vesicle-Associated Membrane Protein 2; C095992:complexin I