Acetylcholinesterase (AChE) plays a pivotal role in the synaptic transmission in the cholinergic nervous system of most animals, including insects. Most insects possess two AChEs (i.e., AChE1 vs. AChE2), which are encoded by two paralogous loci originated from the duplication that occurred before the radiation of insects. The phylogenetic analysis suggested that the last common ancestor of ace1 and ace2 shared its origin with those of Platyhelminthes. In addition, ace1 lineage showed a lower evolutionary rate (d and dN/dS ratio) compared to ace2 lineage, suggesting that the ace1 lineage has maintained relatively more essential functions following duplication. Furthermore, structural modeling of AChEs revealed that consistent structural alteration in their active-site gorge topology was caused by amino acid substitution, likely leads to functional differentiation between two AChEs. The functional transition of ace in some hymenopteran insects appears to have occurred by only a few mutations resulting in dramatic alteration of AChE activity. Taken together, our findings provide basic information on when the ace duplication occurred and what structural features have been associated with the differentiation of two AChEs during evolution.

• Deok Jea Cha(Highland Agriculture Research Center, National Institute of Crop Science, RDA, Department of Agricultural Biotechnology, Seoul National University)
• Si Hyeock Lee(Department of Agricultural Biotechnology, Seoul National University)