Nematode Acetylcholinesterases are Encoded by Multiple Genes and Perform Non-Overlapping Functions

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Journal Title, Volume, Page: 
Chemico-Biological Interactions Volumes 157-158, 15 December 2005, Pages 263-268
Year of Publication: 
Ayman S. Hussein
Faculty of Science, An-Najah National University, PO Box 7, Nablus, Palestine
Current Affiliation: 
Faculty of Medicine & Health Sciences, Department of Biomedical Sciences, An-Najah National University, Nablus, Palestine
Murray E. Selkirk
Division of Cell and Molecular Biology, Imperial College London, London SW7 2AY, UK
Ovadia Lazari
Department of Veterinary Clinical Science, University of Liverpool, South Wirral, CH64 7TE, UK
Jacqueline B. Matthews
Division of Parasitology, Moredun Research Institute, Midlothian EH26 OPZ, UK
Preferred Abstract (Original): 

Nematodes are unusual in that diverse molecular forms of acetylcholinesterase are the product of distinct genes. This is best characterised in the free living organism Caenorhabditis elegans, in which 3 genes are known to give rise to distinct enzymes, with a fourth likely to be non-functional. ACE-1 is an amphiphilic tetramer associated with a hydrophobic non-catalytic subunit, analogous to vertebrate T enzymes, whereas ACE-2 and ACE-3 are glycosylphosphatidylinositol-linked amphiphilic dimers. The different ace genes show distinct anatomical patterns of expression in muscles, sensory neurons and motor neurons, with only a few examples of coordinated expression. Clear homologues of ace-1 and ace-2 have now been isolated from a variety of parasitic nematodes, and the predicted proteins have very similar C-terminal amino acid sequences, implying an analogous means of anchorage to membranes. In addition to these membrane-bound enzymes, many parasitic nematodes which colonise mucosal surfaces secrete acetylcholinesterases to the external (host) environment. These hydrophilic enzymes are separately encoded in the genome, so that some parasites may thus have a total complement of six ace genes. The secretory enzymes have been characterised from the intestinal nematode Nippostrongylus brasiliensis and the lungworm Dictyocaulus viviparus. These show a number of common features, including a truncated C-terminus and an insertion at the molecular surface, when compared to other nematode acetylcholinesterases. Although the function of these enzymes has not been determined, they most likely alter host physiological responses to promote survival of the parasite.

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