The vast majority of newly synthesized acetylcholinesterase (AChE) molecules do not assemble into catalytically active oligomeric forms and are rapidly degraded intracellularly by the endoplasmic reticulum associated protein degradation pathway. We have previously shown that AChE in skeletal muscle is regulated in part posttranslationally by the availability of the non-catalytic subunit collagen Q (ColQ), and others have shown that expression of a 17 amino acid N-terminal proline rich attachment domain of ColQ (PRAD) is sufficient to promote AChE tetramerization in cells producing AChE. In the present study we show that muscle cells, or cell lines expressing AChE catalytic subunits, incubated with synthetic PRA... More
The vast majority of newly synthesized acetylcholinesterase (AChE) molecules do not assemble into catalytically active oligomeric forms and are rapidly degraded intracellularly by the endoplasmic reticulum associated protein degradation pathway. We have previously shown that AChE in skeletal muscle is regulated in part posttranslationally by the availability of the non-catalytic subunit collagen Q (ColQ), and others have shown that expression of a 17 amino acid N-terminal proline rich attachment domain of ColQ (PRAD) is sufficient to promote AChE tetramerization in cells producing AChE. In the present study we show that muscle cells, or cell lines expressing AChE catalytic subunits, incubated with synthetic PRAD peptides containing the endoplasmic reticulum retrieval sequence KDEL take up and retrogradely transport them to the ER network where they induce assembly of AChE tetramers. The peptides act to enhance AChE folding thereby rescuing them from ER degradation. This enhanced folding efficiency occurs in the presence of inhibitors of protein synthesis and in turn increases total cell associated AChE activity and active tetramer secretion. Pulse chase studies of isotopically labeled AChE molecules show that the enzyme is rescued from intracellular degradation. These studies provide a mechanistic explanation for the large scale intracellular degradation of AChE previously observed and indicate that simple peptides alone can increase the production and secretion of this critical synaptic enzyme in muscle tissue.
