title: Phosphorylation of syntaxin 3B by CaMKII regulates the formation of t-SNARE complexes.
abstract: Ribbon synapses in the retina lack the t-SNARE (target-soluble N-ethylmaleimide-sensitive factor attachment protein receptor) syntaxin 1A that is found in conventional synapses of the nervous system, but instead contain the related isoform syntaxin 3B. Previous studies have demonstrated that syntaxin 3B is essential for synaptic vesicle exocytosis in ribbon synapses, but syntaxin 3B is less efficient than syntaxin 1A in binding the t-SNARE protein SNAP-25 and catalyzing vesicle fusion. We demonstrate here that syntaxin 3B is localized mainly on the presynaptic membrane of retinal ribbon synapses and that a subset of syntaxin 3B is localized in close proximity to the synaptic ribbon. We show further, that syntaxin 3B can be phosphorylated by the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). We determine that the phosphorylation site is located close to the N-terminus at T14. Syntaxin 3B with a phosphomimetic mutation (T14E) had a stronger binding affinity for SNAP-25 compared with wild type syntaxin 3B. We propose that phosphorylation of syntaxin 3B by CaMKII can modulate the assembly of the SNARE complex in ribbon synapses of the retina, and might regulate the exocytosis of synaptic vesicles in ribbon synapses.
authors.affiliation: Department of Neurobiology and Anatomy, The University of Texas Medical School, Houston, United States.
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Neurobiology and Anatomy, The University of Texas Medical School, Houston, United States.
authors.forename: Ruth
authors.initials: R
authors.lastname: Heidelberger
authors.affiliation: Department of Neurobiology and Anatomy, The University of Texas Medical School, Houston, United States. Electronic address: Roger.Janz@uth.tmc.edu.
authors.forename: Roger
authors.initials: R
authors.lastname: Janz
mesh_terms: D000818:Animals; D001665:Binding Sites; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D005089:Exocytosis; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D010766:Phosphorylation; D017729:Presynaptic Terminals / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism*
chemical_list: D050765:Qa-SNARE Proteins; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2
keywords: Munc18; Retina; Ribbon synapse; SNAP-25; SNARE complex