Syntaxin1A lateral diffusion reveals transient and local SNARE interactions

At the synapse, vesicles stably dock at the active zone. However, in cellular membranes, proteins undergo a diffusive motion. It is not known how the motion of membrane proteins involved in vesicle exocytosis is compatible with both vesicle docking and the dynamic remodeling of the plasma membrane imposed by cycles of exocytosis and endocytosis. To address this question, we studied the motion of the presynaptic membrane protein syntaxin1A at both the population and single-molecule levels in primary cultures of rat spinal cord neurons. Syntaxin1A was rapidly exchanged between synaptic and extrasynaptic regions. Changes in syntaxin1A mobility were associated with interactions related to the formation of the exocytotic complex. Finally, we propose a reaction-diffusion model reconciling the observed diffusive properties of syntaxin at the population level and at the molecular level. This work allows us to describe the diffusive behavior and kinetics of interactions between syntaxin1A and its partners that lead to its transient stabilization at the synapse.