Hsp90 is involved in the entry of clostridial neurotoxins into the cytosol of nerve terminals

Abstract

Botulinum and tetanus neurotoxins are the most toxic substances known and form the growing family of clostridial neurotoxins. They are composed of a metalloprotease light chain (L), linked via a disulfide bond to a heavy chain (H). H mediates the binding to nerve terminals and the membrane translocation of L into the cytosol where their substrates, the three SNARE proteins, are localised. L translocation is accompanied by unfolding, and it has to be reduced and reacquire the native fold to exert its neurotoxicity. The Thioredoxin reductase-Thioredoxin system is responsible for the reduction, but it is unknown whether the refolding of L is spontaneous or aided by host chaperones. Here we report that geldanamycin, a specific inhibitor of heat shock protein 90, hampers the refolding of L after membrane translocation and completely prevents the cleavage of SNAREs. We also found that geldanamycin strongly synergises with PX-12, an inhibitor of thioredoxin, suggesting that the processes of L chain refolding and interchain disulfide reduction are strictly coupled. Indeed we found that the heat shock protein 90 and the Thioredoxin reductase-Thioredoxin system physically interact on synaptic vesicle where they orchestrate a chaperone-redox machinery which is exploited by clostridial neurotoxins to deliver their catalytic part into the cytosol.

Botulinum Neurotoxin: A Multifunctional Protein for the Development of New Therapeutics

“…In both models, the reduction of the disulphide bond is essential to free the LC at the end of the translocation step, and the enzyme thioredoxin and its regenerating enzyme thioredoxin reductase have been identified as the cellular system responsible for the reduction of the disulphide bridge [61]. Following translocation, another key protein recently identified is Hsp 90, which may act as a chaperone assisting the refolding of the LC once in the cytosol [62].…”

A binding motif for Hsp90 in the A chains of ADP‐ribosylating toxins that move from the endoplasmic reticulum to the cytosol

“…Hsp90 is also active in the endosome‐to‐cytosol translocation of AB‐type ADP‐ribosylating toxins (ADPRTs), but it is not required for the endosomal translocation of most AB toxins with different catalytic activities (Azarnia Tehran et al, ; Dmochewitz et al, ; Haug, Aktories, & Barth, ; Haug et al, ; Kaiser et al, ; Lang et al, ; Ratts et al, ; Schuster et al, ; Steinemann, Schlosser, Jank, & Aktories, ). Likewise, Hsp90 is not needed to complete the intoxication process for three ER‐translocating toxins that are not ADPRTs: Shiga toxin 1 (Stx1), Shiga toxin 2 (Stx2), and ricin (Spooner et al, ; Taylor, Britt, Fundora, & Teter, ).…”

Neurophysiological Measures of Efficacy and Safety for Botulinum Toxin Injection in Facial and Bulbar Muscles: Special Considerations

“…The heavy chain of BoNT mediates the binding to nerve terminals and the membrane translocation of the light chains into the cytosol, where the substrates of BoNT, namely the three SNARE proteins (VAMP, SNAP25, and syntaxin), are localised. Recently, it was described that the heat shock protein Hsp90 is involved in the entry of clostridial neurotoxins into the cytosol of nerve terminals [ 5 , 6 , 7 ]. The subsequent effect of BoNT is mediated by the inhibition of acetylcholine release from the motor nerve terminal into the neuromuscular junction [ 8 ].…”