The Clostridium botulinum neurotoxins (BoNTs) are the most potent protein toxins known to humans.
There are seven serotypes of the BoNTs (AeG), among which serotypes A, B, E and F are known to cause
natural human intoxication. To date, eleven subtypes of LC/E, termed E1~E11, have been identified. The
LCs of BoNT/E were insoluble, prohibiting studies towards understanding the mechanisms of toxin action
and substrate recognition. In this work, the molecular basis of insolubility of the recombinant LCs of two
representative subtypes of BoNT/E, E1(Beluga) and E3 (Alaska), was determined. Hydrophobicity profile
and structural modeling predicted a C-terminal candidate region responsible for the insolubility of LC/Es.
Deletion of C-terminal 19 residues of LC/E(1-400) resulted in enhanced solubility, from 2 to ~50% for LC/
EAlaska and from 16 to ~95% for LC/EBeluga. In addition, resides 230e236 were found to contribute to a
different solubility level of LC/EAlaska when compared to LC/EBeluga. Substituting residues 230TCI232 in LC/
EAlaska to the corresponding residues of 230KYT232 in LC/EBeluga enhanced the solubility of LC/EAlaska to a
level approaching that of LC/EBeluga. Among these LC/Es and their derivatives, LC/EBeluga 1-400 was the
most soluble and stable protein. Each LC/E derivative possessed similar catalytic activity, suggesting that
the C-terminal region of LC/Es contributed to protein solubility, but not catalytic activity. In conclusion,
this study generated a soluble and stable recombinant LC/E and provided insight into the structural
components that govern the solubility and stability of the LCs of other BoNT serotypes and Tetanus toxin.
The Clostridium botulinum neurotoxins (BoNTs) are the most potent protein toxins known to humans.There are seven serotypes of the BoNTs (AeG), among which serotypes A, B, E and F are known to causenatural human intoxication. To date, eleven subtypes of LC/E, termed E1~E11, have been identified. TheLCs of BoNT/E were insoluble, prohibiting studies towards understanding the mechanisms of toxin actionand substrate recognition. In this work, the molecular basis of insolubility of the recombinant LCs of tworepresentative subtypes of BoNT/E, E1(Beluga) and E3 (Alaska), was determined. Hydrophobicity profileand structural modeling predicted a C-terminal candidate region responsible for the insolubility of LC/Es.Deletion of C-terminal 19 residues of LC/E(1-400) resulted in enhanced solubility, from 2 to ~50% for LC/EAlaska and from 16 to ~95% for LC/EBeluga. In addition, resides 230e236 were found to contribute to adifferent solubility level of LC/EAlaska when compared to LC/EBeluga. Substituting residues 230TCI232 in LC/EAlaska to the corresponding residues of 230KYT232 in LC/EBeluga enhanced the solubility of LC/EAlaska to alevel approaching that of LC/EBeluga. Among these LC/Es and their derivatives, LC/EBeluga 1-400 was themost soluble and stable protein. Each LC/E derivative possessed similar catalytic activity, suggesting thatthe C-terminal region of LC/Es contributed to protein solubility, but not catalytic activity. In conclusion,this study generated a soluble and stable recombinant LC/E and provided insight into the structural
components that govern the solubility and stability of the LCs of other BoNT serotypes and Tetanus toxin.
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