Tetanus Neurotoxin: Potential Mechanism for Drug Delivery

Tetanus neurotoxin (TeNT), produced by Clostridium tetani, is one of the most potent neurotoxins in humans. TeNT causes tetanus, which is characterized by painful muscular contractions and spasms as well as seizure. TeNT is composed of a light chain and a heavy chain (TTH). The toxic properties of TeNT reside in the toxin light chain (L), but like complete TeNT, the TeNT heavy chain (TTH) and the C-terminal domain (TTC) alone can bind and enter into neurons.

Based on these properties, a recent publication (1) considered that TTC could be a promising vehicle to deliver drug cargos to neurons. To explore this possibility, they engineered fusion proteins containing various Tetanus neurotoxin fragments. They chose B-cell leukemia/lymphoma 2 protein (Bcl-2) as a partner protein, because Bcl-2 is one of the most potent anti-apoptotic proteins and has an appropriate size (26kDa) to act as a fusion partner.

They tested these fusion proteins in both cell-based and cell-free protein expression systems to determine whether the purified fusion products retained both anti-apoptotic and neuronal migration properties. One construct (Bcl2-hTTC) exhibited neuronal binding and prevented cell death of neuronal PC12 cells induced by serum and NGF deprivation, as evidenced by the inhibition of cytochrome C release from the mitochondria. For in vivo assays, Bcl2-hTTC was injected into the tongues of mice and was seen to selectively migrate to hypoglossal nuclei mouse brain stems.

  1. Watanbe, Y. et. al. (2018) Tetanus toxin fragments and Bcl-2 fusion proteins : cytoprotection and retrograde axonal migration. BMC Biotechnology 18, 39.

ProTEV Protease Compound Compatibility Analysis

Cleavage of 20µg of GST-MBP fusion protein with ProTEV protease after 60 minutes at 30°C.
Cleavage of 20µg of GST-MBP fusion protein with ProTEV protease after 60 minutes at 30°C.

Many proteins are expressed as fusion partners with affinity tags, such as the HaloTag® fusion, glutathione-S-transferase (GST) or maltose binding protein (MBP), to selectively bind the proteins using affinity purification resins. While such resins yield high-purity protein quickly, the large affinity tags are undesirable for some downstream applications. Most expression vectors are designed with a specific protein cleavage site between the two fusion partners to remove the affinity tag after purification. ProTEV Protease recognizes a rare amino acid sequence, EXXYXQ, where X is any amino acid, and cleaves after the glutamine residue.

ProTEV Plus functions over a broad pH and temperature range. In a recent study the enzymatic activity of ProTEV Plus in the presence of various compounds (Table 1) commonly found in protein purification protocols were evaluated.

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