Cationic neurotoxins
Engineered clostridial toxins comprising an amino acid modification that increases the isoelectric point of the engineered clostridial toxin to a value that is at least 0.2 pI units higher than the isoelectric point of an otherwise identical clostridial toxin lacking the modification, wherein the modification is not located in the clostridial toxin binding domain (H C domain).
1. An engineered clostridial toxin comprising an amino acid modification that increases the isoelectric point of the toxin to a value that is at least 0.2 pI units higher than the isoelectric point of an otherwise identical toxin lacking the modification, wherein the modification is not located in the clostridial toxin binding domain and the clostridial light chain does not contain an E3 ligase recognition motif.
2. An engineered clostridial toxin comprising an amino acid modification located in the clostridial toxin translocation domain that increases the isoelectric point of the toxin to a value that is at least 0.2 pI units higher than the isoelectric point of an otherwise identical toxin lacking the modification.
3. The toxin of claim 1 , wherein the modification increases the isoelectric point of the toxin to a value that is at least 0.5 pI units higher than the isoelectric point of an otherwise identical clostridial toxin lacking the modification.
4. The toxin of claim 1 , wherein the modification increases the isoelectric point of the toxin to a value that is between 2 and 5 pI units higher than the isoelectric point of an otherwise identical clostridial toxin lacking the modification.
5. The toxin of claim 1 , having an isoelectric point of at least 6.5.
6. The toxin of claim 1 having an isoelectric point of between 6.5 and 7.5.
7. The toxin of claim 1 , wherein the modification is an amino acid substitution, an amino acid insertion, or an amino acid deletion.
8. The toxin of claim 7 , wherein the modification is a substitution of an acidic amino acid residue with a basic amino acid residue, a substitution of an acidic amino acid residue with an uncharged amino acid residue, or a substitution of an uncharged amino acid residue with a basic amino acid residue.
9. The toxin of claim 1 , comprising from 1 to 90 amino acid modifications.
10. The toxin of claim 1 , comprising at least three amino acid modifications.
11. The toxin of claim 1 , comprising from 4 to 40 amino acid modifications.
12. The toxin of claim 1 , wherein the modification is to a surface exposed amino acid residue.
13. The toxin of claim 1 , wherein the modification is to an amino acid residue selected from: aspartic acid, glutamic acid, histidine, asparagine, glutamine, serine, threonine, alanine, glycine, valine, leucine, and isoleucine.
14. The toxin of claim 13 , wherein the amino acid residue is substituted with lysine or arginine.
15. The toxin of claim 1 , wherein the toxin is BoNT/E and the amino acid modification does not involve a substitution with lysine at Q53, N72, N378, N379, R394, or T400.
16. A nucleic acid comprising a nucleic acid sequence encoding the toxin of claim 1 .
17. A method of producing a single-chain engineered clostridial toxin protein having a light chain and a heavy chain, the method comprising expressing the nucleic acid of claim 16 in a suitable host cell, lysing the host cell to provide a host cell homogenate containing the single-chain engineered clostridial toxin protein, and isolating the single-chain engineered clostridial toxin protein.
18. A method of activating an engineered clostridial toxin, the method comprising providing a single-chain engineered clostridial toxin protein obtainable by the method of claim 17 , contacting the protein with a protease that cleaves the protein at a recognition site located between the light chain and heavy chain, and converting the protein into a di-chain polypeptide wherein the light chain and heavy chain are joined together by a disulphide bond.