High-level secretion and purification of recombinant acetylcholinesterase from human cerebral tissue in P. pastoris and identification by chromogenic reaction

Enhanced pesticide sensitivity of novel housefly acetylcholinesterases: a new tool for the detection of residual pesticide contamination

The full-length cDNA encoding an acetylcholinesterase (AChE) was cloned and sequenced from the housefly, Musca domestica, by reverse transcriptase-polymerase chain reaction (RT-PCR). Sequence analysis revealed that this 2,076 bp sequence encodes a mature protein of 612 amino acids (67 kDa) and a 79 residue signal peptide. The amino acid sequence shared 52.8-81.4% identity with the AChE proteins of other insects. The cDNA sequence, which lacked the signal peptide was inserted into the vector pPIC9K and then introduced into strain GS115 of the yeast Pichia pastoris. The recombinant AChE protein was then expressed in P. pastoris strain GS115 by methanol induction. Site-directed mutagenesis of the A262G, Y327F, Y327D and I374D residues, either singly or in combination, was performed by reverse PCR. These mutants improved the catalytic activity and sensitivity to the organophosphate and carbamate insecticides. Although the sensitivity of other mutants was slightly increased, the results still showed that the sensitivity of triple mutant, GDD (A262G/Y327D/I374D), enhanced remarkably as much as 16 times for methomyl, 14 times for both carbofuran and chlorpyrifos, and ten times for parathion-methyl, compared to that of the wild-type. The results strongly suggested that these residues are the key structural elements controlling AChE enzyme catalytic activity and sensitivity to inhibition by insecticides. The AChE enzyme obtained by this method could be used to detect the organophosphate and carbamate insecticide residues in fruits and vegetables, a characteristic of great potential research and industrial application.

Cloning and expression of carp acetylcholinesterase gene in Pichia pastoris and characterization of the recombinant enzyme

The gene encoding acetylcholinesterase (AChE) was cloned from common carp muscle tissue. The full-length cDNA was 2368 bp that contains a coding region of 1902 bp, corresponding to a protein of 634 amino acids. The deduced amino acid sequence showed a significant homology with those of ichthyic AChEs and several common features among them, including T peptide encoded by exon T in the C-terminus. Three yeast expression vectors were constructed and introduced into the yeast Pichia pastoris. The transformant harboring carp AChE gene lacking exon T most effectively produced AChE activity extracellularly. The replacement of the native signal sequence with the yeast alpha-factor prepro signal sequence rather decreased the production. A decrease in cultivation temperature from 30 to 15 degrees C increased the activity production 32.8-fold. The purified recombinant AChE lacking T peptide, eluted as a single peak with a molecular mass of about 230 kDa on the gel filtration chromatography, exhibited the specific activity of 4970 U/mg. On the SDS-PAGE, three proteins with molecular masses of 73, 54, and 22 kDa were observed. These proteins were N-glycosylated, and their N-terminal sequence showed that the latter two were produced from the former probably by proteolytic cleavage at the C-terminal region. Thus, the recombinant AChE is homotrimer of three identical subunits with 73 kDa. The optimal temperature and pH of the recombinant were comparable to those of the native enzyme purified previously, but the values of kinetic parameters and the sensitivities to substrate inhibition and inhibitors were considerably different between them.