TY - JOUR
T1 - The SNAP-25 linker as an adaptation toward fast exocytosis
AU - Nagy, Gábor
AU - Milosevic, Ira
AU - Mohrmann, Ralf
AU - Wiederhold, Katrin
AU - Walter, Alexander M
AU - Sørensen, Jakob B
N1 - Keywords: Amino Acid Sequence; Animals; Cattle; Chromaffin Cells; Electrophysiology; Exocytosis; Gene Expression Regulation; Humans; Mice; Molecular Sequence Data; Qb-SNARE Proteins; Qc-SNARE Proteins; Recombinant Fusion Proteins; Sequence Homology, Amino Acid; Synaptosomal-Associated Protein 25; Synaptosomes
PY - 2008
Y1 - 2008
N2 - The assembly of four soluble N-ethylmaleimide-sensitive factor attachment protein receptor domains into a complex is essential for membrane fusion. In most cases, the four SNARE-domains are encoded by separate membrane-targeted proteins. However, in the exocytotic pathway, two SNARE-domains are present in one protein, connected by a flexible linker. The significance of this arrangement is unknown. We characterized the role of the linker in SNAP-25, a neuronal SNARE, by using overexpression techniques in synaptosomal-associated protein of 25 kDa (SNAP-25) null mouse chromaffin cells and fast electrophysiological techniques. We confirm that the palmitoylated linker-cysteines are important for membrane association. A SNAP-25 mutant without cysteines supported exocytosis, but the fusion rate was slowed down and the fusion pore duration prolonged. Using chimeric proteins between SNAP-25 and its ubiquitous homologue SNAP-23, we show that the cysteine-containing part of the linkers is interchangeable. However, a stretch of 10 hydrophobic and charged amino acids in the C-terminal half of the SNAP-25 linker is required for fast exocytosis and in its absence the calcium dependence of exocytosis is shifted toward higher concentrations. The SNAP-25 linker therefore might have evolved as an adaptation toward calcium triggering and a high rate of execution of the fusion process, those features that distinguish exocytosis from other membrane fusion pathways.
AB - The assembly of four soluble N-ethylmaleimide-sensitive factor attachment protein receptor domains into a complex is essential for membrane fusion. In most cases, the four SNARE-domains are encoded by separate membrane-targeted proteins. However, in the exocytotic pathway, two SNARE-domains are present in one protein, connected by a flexible linker. The significance of this arrangement is unknown. We characterized the role of the linker in SNAP-25, a neuronal SNARE, by using overexpression techniques in synaptosomal-associated protein of 25 kDa (SNAP-25) null mouse chromaffin cells and fast electrophysiological techniques. We confirm that the palmitoylated linker-cysteines are important for membrane association. A SNAP-25 mutant without cysteines supported exocytosis, but the fusion rate was slowed down and the fusion pore duration prolonged. Using chimeric proteins between SNAP-25 and its ubiquitous homologue SNAP-23, we show that the cysteine-containing part of the linkers is interchangeable. However, a stretch of 10 hydrophobic and charged amino acids in the C-terminal half of the SNAP-25 linker is required for fast exocytosis and in its absence the calcium dependence of exocytosis is shifted toward higher concentrations. The SNAP-25 linker therefore might have evolved as an adaptation toward calcium triggering and a high rate of execution of the fusion process, those features that distinguish exocytosis from other membrane fusion pathways.
U2 - 10.1091/mbc.E07-12-1218
DO - 10.1091/mbc.E07-12-1218
M3 - Journal article
C2 - 18579690
SN - 1059-1524
VL - 19
SP - 3769
EP - 3781
JO - Molecular Biology of the Cell
JF - Molecular Biology of the Cell
IS - 9
ER -