FIGURE 23.7 Uptake of Botulinum Toxin Current view of botulinum toxin entry at nerve terminals. (1) Toxin binds to the nerve cell membrane at an as-yetunidentified receptor. (2) Internalization inside endocytotic vesicles, whose interior is acidified by an ATP-driven proton pump. (3) At low pH, the toxin changes conformation and inserts into the vesicle membrane. The light chain (red) is released into the cytosol. (4) In the cytosol the light chain degrades one of the three SNARE proteins

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