Asymmetric acetylcholinesterase is assembled in the Golgi apparatus

Abstract

The synthesis, assembly, and processing of the multiple molecular forms of acetylcholinesterase (AcChoEase; acetylcholine acetylhydrolase, EC 3.1.1.7) in quail muscle cultures was studied by using lectins to distinguish enzyme molecules residing in different subcellular compartments. Special emphasis was given to the assembly of asymmetric AcChoEase molecules because these appear to be the predominant, if not unique, forms of AcChoEase at the vertebrate neuromuscular junction. All cell surface and secreted AcChoEase forms bind to immobilized wheat germ agglutinin, ricin, and concanavalin A, indicating that they have complex oligosaccharides. After treatment of muscle cells with a membrane-permeable irreversible AcChoEase inhibitor, there is a rapid reappearance of the globular monomeric, dimeric, and tetrameric AcChoEase forms. However, the collagen-tailed asymmetric form does not appear until about 90 min after treatment. Analysis of the AcChoEase oligosaccharides with lectins indicates maturation to complex forms over a 90-min period. A large fraction of the intracellular globular AcChoEase molecules bind only to concanavalin A, indicating that they are assembled in the rough endoplasmic reticulum. In contrast, all intracellular asymmetric AcChoEase binds to wheat germ agglutinin, and a significant fraction binds to ricin, indicating that this unique AcChoEase form is assembled from subunits that have previously acquired complex sugars. I conclude that assembly of asymmetric AcChoEase, hence acquisition of information specifying basal lamina localization, occurs in the Golgi apparatus.