The effect of engineered disulfide bonds on the stability of Drosophila melanogaster acetylcholinesterase.
BACKGROUND
Acetylcholinesterase is irreversibly inhibited by organophosphate and carbamate insecticides allowing its use in biosensors for detection of these insecticides. Drosophila acetylcholinesterase is the most sensitive enzyme known and has been improved by in vitro mutagenesis. However, its stability has to be improved for extensive utilization.


RESULTS
To create a disulfide bond that could increase the stability of the Drosophila melanogaster acetylcholinesterase, we selected seven positions taking into account first the distance between Cbeta of two residues, in which newly introduced cysteines will form the new disulfide bond and second the conservation of the residues in the cholinesterase family. Most disulfide bonds tested did not increase and even decreased the stability of the protein. However, one engineered disulfide bridge, I327C/D375C showed significant stability increase toward denaturation by temperature (170 fold at 50 degrees C), urea, organic solvent and provided resistance to protease degradation. The new disulfide bridge links the N-terminal domain (first 356 aa) to the C-terminal domain. The quantities produced by this mutant were the same as in wild-type flies.


CONCLUSIONS
Addition of a disulfide bridge may either stabilize or unstabilize proteins. One bond out of the 7 tested provided significant stabilisation.
Siadat
Omid Ranaei
OR
IPBS-CNRS 205 route de Narbonne, Toulouse, France. ranaei@irnewideas.ir
Lougarre
Andrée
A
Lamouroux
Lucille
L
Ladurantie
Caroline
C
Fournier
Didier
D