Electrostatic anchoring of SNAP25 to the plasma membrane

Abstract

Neurotransmission is based on incredibly rapid membrane trafficking cycles, mediating the release of neurotransmitters. The fusion machinery of the well-studied SNARE protein complex ensures the speed and precision of synaptic transmission. One critical part of this machinery is the initially cytosolic SNARE protein SNAP25, which needs to be in constant supply at the active zones of the plasma membrane. <br /> The focus of this study lies on the investigation of the self-organizational principle underlying the plasma membrane targeting of SNAP25, an aspect that has not yet been extensively studied. Over the course of this study, the existence of an electrostatic anchoring mechanism is revealed, which mediates the initial contact of SNAP25 to the plasma membrane. <br /> A small polybasic cluster present in the cysteine-rich region of SNAP25 is responsible for the electrostatic anchoring. To characterize this region, different SNAP25 mutant constructs are mainly analyzed via confocal laser scanning microscopy, to reveal differences in SNAP25’s localization. <br /> Although previous studies suggested similar anchoring mechanisms based on electrostatic interactions, the results presented show that the comparatively small cluster is sufficient to facilitate initial membrane contact in the case of the neuronal SNAP25 and its ubiquitously expressed homologue SNAP23. The study further identifies the potential lipid interaction partner PIP² as the most likely candidate for SNAP25’s electrostatic anchoring mechanism. This for SNAP25 newly discovered electrostatic anchoring mechanism, reliant on only a small polybasic cluster, represents an extension of previous theories of plasma membrane targeting via electrostatic interactions and could have potential generality, as other proteins might use a similar electrostatic anchor.