Tetanus (TeNT) is a zinc protease that blocks neurotransmission by cleaving the synaptic protein vesicle-associated membrane protein/synaptobrevin. Although its intracellular catalytic activity is well established, the mechanism by which this neurotoxin interacts with the neuronal surface is not known. In this study, we characterize p15s, the first plasma membrane TeNT binding proteins and we show that they are glycosylphosphatidylinositol-anchored glycoproteins in nerve growth factor (NGF)-differentiated PC12 cells, spinal cord cells, and purified motor neurons. We identify p15 as neuronal Thy-1 in NGF-differentiated PC12 cells. Fluorescence lifetime imaging microscopy measurements confirm the close association of the binding domain of TeNT and Thy-1 at the plasma membrane. We find that TeNT is recruited to detergent-insoluble lipid microdomains on the surface of neuronal cells. Finally, we show that cholesterol depletion affects a raft subpool and blocks the internalization and intracellular activity of the toxin. Our results indicate that TeNT interacts with target cells by binding to lipid rafts and that cholesterol is required for TeNT internalization and/or trafficking in neurons.
INTRODUCTIONTetanus (TeNT) and botulinum neurotoxins (BoNTs) block neurotransmitter release and are responsible for tetanus and botulism, respectively. These toxins share a common structure comprised of a heavy (H, 100 kDa) and a light (L, 50 kDa) chain linked by a disulfide bond. The H chain mediates binding and internalization in neurons, whereas the L chain is a metallo-protease that selectively cleaves synaptic proteins (Niemann et al., 1994;Schiavo et al., 2000). TeNT and BoNTs bind to the neuromuscular junction, but their intracellular actions take place at different levels of the nervous system. TeNT undergoes retrograde transport to the cell body of spinal cord motor neurons (MNs), is transcytosed, and cleaves the synaptic vesicle protein vesicle-associated membrane protein (VAMP)/synaptobrevin in inhibitory synapses. Instead, BoNTs act at a peripheral level by blocking acetylcholine release at the motor nerve terminal. This differential sorting has been interpreted as a consequence of binding to different surface receptors (Habermann and Dreyer, 1986;Herreros et al., 1999).TeNT and BoNTs bind to polysialogangliosides of the G1b series (Halpern and Neale, 1995). However, the fact that their binding is sensitive to proteases (Lazarovici and Yavin, 1986;Pierce et al., 1986;Yavin and Nathan, 1986) suggests the existence of specific protein receptors. Thus, a model in which TeNT and BoNTs interact with a complex constituted by both lipid and protein receptors has been proposed (Montecucco, 1986). Despite several efforts, these protein receptors have not been conclusively identified. Several BoNT serotypes interact with synaptotagmins (Nishiki et al., 1994;Li and Singh, 1998), but the role of these proteins as physiological BoNT receptors remains controversial (Evans et al., 1986;Bakry et al., 1997). We have previously followe...