title: The butyrylcholinesterase K-variant shows similar cellular protein turnover and quaternary interaction to the wild-type enzyme.
abstract: A recent study has linked the butyrylcholinesterase (BChE) K-variant and the apolipoprotein epsilon4 isoform to late-onset Alzheimer's disease. These findings have been controversial and have led us to examine the differences between wild-type and K-variant BChE in enzyme activity, protein stability, and quaternary structure. J-variant BChE (E497V/A539T) was also studied because it is associated with the K-variant mutation. The K-variant mutation (A539T) is located in the C-terminal tetramerization domain. Wild-type, K-variant, and J-variant BChE were expressed in Chinese hamster ovary cells and purified. The purified enzymes had similar binding affinity (Km) values and catalytic rates for butyrylthiocholine and benzoylcholine. In pulse-chase studies the K-variant, J-variant, and wildtype BChE were degraded rapidly within the cell, with a half-time of approximately 1.5 h. Less than 5% of the intracellular BChE was exported. The C-terminal peptide containing the K-variant mutation interacted with itself as strongly as did the wild-type peptide in the yeast two-hybrid system. Both K-variant and wild-type BChE assembled into tetramers in the presence of poly-L-proline or the proline-rich attachment domain of the collagen tail. The native K-variant BChE in serum showed the same proportion of tetramers as the native serum wild-type BChE. We conclude that the K-variant BChE is similar to wild-type BChE in enzyme activity, protein turnover, and tetramer formation.
authors.affiliation: Department of Biochemistry and Molecular Biology and Eppley Institute, University of Nebraska Medical Center, Omaha 68198-6805, USA.
authors.forename: C V
authors.initials: CV
authors.lastname: Altamirano
authors.forename: C F
authors.initials: CF
authors.lastname: Bartels
authors.forename: O
authors.initials: O
authors.lastname: Lockridge
mesh_terms: D000328:Adult; D000818:Animals; D002091:Butyrylcholinesterase / Q000097:blood / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016466:CHO Cells / Q000378:metabolism; D002384:Catalysis; D006224:Cricetinae; D005260:Female; D005787:Gene Frequency; D014644:Genetic Variation / Q000502:physiology*; D006801:Humans; D008297:Male; D009154:Mutation / Q000502:physiology; D020836:Protein Structure, Quaternary
chemical_list: D002091:Butyrylcholinesterase