Molecular characterization of an acetylcholinesterase from the hemichordate Saccoglossus kowalevskii
Résumé
Our goal is to understand the evolution of the structure and function of cholinesterases (ChEs) in the deuterostome lineage and in particular to understand the role of paralogous enzymes such as the acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) of the vertebrates. We have, in the past, characterized ChEs in two acraniate deuterostomes: amphioxus (a cephalochordate) and Ciona intestinalis (a urochordate). Here we present results on an AChE from a basal deuterostome, a model hemichordate, the acorn worm Saccoglossus kowalevskii. Of the eight genes coding for putative ChE-like proteins possessing Trp84, a characteristic of the choline-binding catalytic subsite of ChEs, we cloned a full length cDNA with a coding sequence typical of an acraniate AChE possessing a C-terminal exon coding for a typical T-peptide. We then used in vitro expression of the cDNA in COS-7 cells to characterize the AChE kinetically, pharmacologically, and biochemically. The cDNA codes for an AChE (AChE1), which is found in monomeric (G(1)), dimeric (G(2)), and tetrameric (G(4)) forms; and interacts with poly-L-proline, PRiMA, and ColQ characteristic of an AChE possessing a T-peptide:The expression of the AChE is temperature dependent, with greater expression at 30 degrees C. We discuss the implications of these data for the evolution of the ChEs in the deuterostomes.