Three acetylcholinesterases of the pinewood nematode, Bursaphelenchus xylophilus: Insights into distinct physiological functions

Acetylcholinesterase (AChE) plays a key role in postsynaptic transmission in most animals. Nematodes encode multiple AChEs, implying its functional diversity. To explore physiological functions of multiple AChEs, three distinct AChEs (BxACE-1, BxACE-2, and BxACE-3) were identified and characterized from the pinewood nematode. Sequencing comparison with Torpedo AChE and Caenorhabditis elegans ACEs identified choline-binding site, catalytic triad functional site, three internal disulfide bonds and aromatic residues for the catalytic gorge. Transcriptional profiling by quantitative real-time PCR revealed that BxACE-3 is more actively transcribed than BxACE-1 (2-3 times) and BxACE-2 (9-18 times) in both propagative and dispersal stages. The three BxACEs were functionally expressed using baculovirus system. Kinetic analysis of in vitro-expressed BxACEs revealed that the substrate specificity was highest in BxACE-1 whereas the catalytic efficiency was highest in BxACE-2. In inhibition assay, BxACE-3 showed the lowest inhibition rate. Taken together, it appears that both BxACE-1 and BxACE-2 play common but non-overlapping roles in synaptic transmission, whereas BxACE-3 may have non-neuronal functions. The current findings should provide valuable insights into the evolutionary process and various physiological roles of AChE.

We characterized the molecular and biochemical properties of three acetylcholinesterases from Bursaphelenchus xylophilus, from which their physiological functions were proposed.125Research highlights▶ Bxace-3 appears to be most abundant, followed by Bxace-1 and Bxace-2. ▶ BxACE-2 is catalytically most efficient, followed by BxACE-1 and BxACE-3. ▶ Both BxACE-1 and BxACE-2 appear to have the classical postsynaptic function. ▶ BxACE-3 is catalytically least active and shows a high tolerance to inhibitors. ▶ BxACE-3 is proposed to have a non-postsynaptic function.