Two cholinesterase activities and genes are present in amphioxus

Area of Science:

• Biochemistry
• Evolutionary Biology
• Molecular Biology

Background:

• Cholinesterases (ChEs), including acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), are crucial enzymes in vertebrate nervous systems.
• Understanding ChE evolution requires examining their presence in basal chordates.
• Previous studies suggested amphioxus has a single ChE activity intermediate to AChE and BuChE.

Purpose of the Study:

• To investigate the cholinesterase activities and genes in the cephalochordate amphioxus.
• To elucidate the evolutionary origins of AChE and BuChE in vertebrates.
• To characterize the pharmacological and kinetic properties of amphioxus ChEs.

Main Methods:

• Enzymological assays using covalent inhibitors to differentiate ChE activities.
• Pharmacological isolation of drug-sensitive and drug-resistant ChE.
• Kinetic analysis of substrate specificity.
• Polymerase chain reaction (PCR) with degenerate primers to identify ChE genes.
• Phylogenetic analysis of deduced protein sequences.

Main Results:

• Amphioxus exhibits two distinct ChE activities: drug-sensitive and drug-resistant.
• Drug-sensitive ChE resembles vertebrate AChE; drug-resistant ChE is similar to fish BuChE or invertebrate ChE.
• Two ChE genes (ChE1 and ChE2) were identified in amphioxus.
• ChE2 possesses an invertebrate-type acyl-binding pocket; ChE1 has a novel acyl-binding site.
• Phylogenetic analysis indicates ChE1 and ChE2 arose from a gene duplication event.

Conclusions:

• Amphioxus possesses two ChE genes and activities, providing a model for early chordate ChE evolution.
• The findings challenge previous assumptions about amphioxus ChE and support a gene duplication model for ChE diversification.
• This study offers critical insights into the evolutionary trajectory of AChE and BuChE within the chordate lineage.