Characterization of two distinct acetylcholinesterases possessing almost identical catalytic activity in a damselfly, Vestalis gracilis

Most insects possess two different acetylcholinesterases (AChEs) (AChE1 and AChE2). It has been recently reported that only one AChE (either AChE1 or AChE2) has been selected as a main synaptic enzyme depending on different insect lineages (Kim et al., 2012; Kim and Lee, 2013). Interastingly, however, both AChE1 and AChE2 were almost equally active in a damselfly species, providing a unique example of incomplete specialization of one AChE function after duplication, where consequently, both AChE1 and AChE2 likely play a similar role in synaptic transmission. In this study, therefore, we investigated the tissue distribution patterns and the molecular and inhibitory properties of two AChEs (VgAChE1 and VgAChE2) from Vestalis gracilis damselfly as a model species possessing two AChEs that are equally active. VgAChEs exhibited almost identical catalytic activity and were expressed in the central nervous system. The most predominant molecular forms of both VgAChEs were disulfide-bridged dimers which are associated with cell membrane by glycosylphosphatidylinositol-anchor. In inhibition assay, however, VgAChE1 and VgAChE2 exhibited different sensitivities to organophosphate and carbamate insecticides depending on the structure of inhibitors. These findings suggest that both VgAChEs have neuronal functions. In addition, soluble monomeric and cleaved molecular forms were detected in both CNS and PNS tissues by AChE2-specific antibody, implying that VgAChE2 likely shares both neuronal and non-neuronal physiological functions in V. gracilis. Our results supported a notion that both VgAChEs, paralogous each other, have still been involved in synaptic transmission, with VgAChE2 being at the early stage of acquiring non-neuronal functions.