Three acetylcholinesterases (ACEs) were identified from the pinewood nematode, Bursaphelenchus xylophilus, and named BxACE-1, BxACE-2, and BxACE-3. Sequence comparison with known ACEs in conjunction with three-dimensional structure analysis suggested that all BxACEs share typical characteristics of ACE but show some differences in the peripheral anionic site. BgACE-3 was most predominantly transcribed, followed by ACE-1 and ACE-2. Immunohistochemistry using anti-BxACEs antibodies revealed that BxACE-1 is most widely distributed whereas BxACE-2 exhibits more localized distribution in neuronal tissues. BxACE-3 was detected from entire body together with some limited tissues, and determined to be soluble. Kinetic analysis of in vitro expressed BxACEs revealed that BxACE-1 has the highest substrate specificity whereas BxACE-2 has the highest catalytic efficiency with BxACE-3 having the lowest catalytic efficiency. Interestingly, presence of BxACE-3 in the pool of BxACEs significantly reduced the inhibition of BxACE-1 and BxACE-2 by inhibitors. Knockout of BxACE-3 by RNAi significantly increased the toxicity of nematicides, supporting the protective role of BxACE-3 against these toxicants. Taken together, BxACE-1 appears to be the major ACE with the function of postsynaptic transmission whereas BxACE-3 has been evolved to acquire the function of chemical defense. BxACE-2 appears to play a role in post-synaptic transmission in specialized neurons.

• Jae Soon Kang(Division of Forest Insect Pests and Diseases, Korea Forest Research and Institute)
• Yil-Sung Moon(Division of Forest Insect Pests and Diseases, Korea Forest Research and Institute)
• Si Hyeock Lee(Department of Agricultural Biotechnology, Seoul National University)