Cryo-electron microscopy of cholinesterases, present and future

Abstract

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) exist in a variety of oligomeric forms, each with defined cellular and subcellular distributions. Although crystal structures of AChE and BChE have been available for many years, structures of the physiologically relevant ChE tetramer were only recently solved by cryo-electron microscopy (cryo-EM) single-particle analysis. Here, we briefly review how these structures contribute to our understanding of cholinesterase oligomerization, highlighting the advantages of using cryo-EM to resolve structures of protein assemblies that cannot be expressed recombinantly. We argue that the next frontier in cholinesterase structural biology is to image membrane-anchored ChE oligomers directly in their native environment-the cell.

Keywords: cholinesterase; cryo-electron microscopy; cryo-electron tomography.

Figure 1

The native butyrylcholinesterase tetramer is a dimer of dimers assembled around a superhelical core. Molecular surface representations of the human butyrylcholinestrase tetramer made up of two canonical dimers (blue and pink) whose C‐terminal tryptophan amphiphilic tetramerization (WAT) helices assemble around a proline‐rich peptide (green). Residues of the catalytic triad (Ser198, Gly325, His438) are painted in yellow. The molecular surface was generated from PDB ID 6I2T, which was fit into the cryo‐EM map EMD‐4400

Figure 2

Cryo‐EM suggests fundamental differences between butyrylcholinesterase and acetylcholinesterase dimers. Catalytic domains of the human butyrylcholinesterase dimer (from PDB ID 6I2T, based on EMD‐4400) are shown in blue, whereas those from human acetylcholinesterase (from PDB ID 3LII) are shown in green