Molecular forms of acetylcholinesterase from Torpedo californica: their relation to synaptic membranes

Abstract

The 16S and 8S forms of acetylcholinesterase (AchE), which are composed of an elongated tail structure in addition to the more globular catalytic subunits, were extracted and purified from membranes from Torpedo californica electric organs. Their subunit compositions and quaternary structures were compared with 11S lytic enzyme which is derived from collagenase or trypsin treatment of the membranes and devoid of the tail unit. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the absence of reducing agent, appreciable populations of monomeric through tetrameric species are observed for the 11S form. Under the same conditions, the 16S form yields only monomer and dimer in addition to a higher molecular weight species. If complete reduction is effected, only the 80,000 molecular weight monomer is dominant for both the 11S and 16S forms. Cross-linking of the 11S form by dimethyl suberimidate followed by reduction yields monomer through tetramer in descending frequency, while the 16S form again shows a high molecular weight species. A comparison of the composition of the 11S and 16S forms reveals that the latter has an increased glycine content, and 1.1 and 0.3 mol % hydroxyproline and hydroxylysine, respectively. Collagenases that have been purified to homogencity and are devoid of amidase and caseinolytic activity, but active against native collagen, will convert 16S acetylcholinesterase to the 11S form. Thus, composition and substrate behavior of the 16S enzyme are indicative of the tail unit containing a collagen-like sequence. A membrane fraction enriched in acetylcholinesterase and components of basement membrane can be separated from the major portion of the membrane protein. The 16S but not the 11S form reassociates selectively with this membrane fraction. These findings reveal distinct similarities between the tail unit of acetylcholinesterase and basement membrane components and suggest a primary association of AchE with the basement membrane.

Localization of the Calcitonin Gene-related Peptide Receptor Complex at the Vertebrate Neuromuscular Junction and Its Role in Regulating Acetylcholinesterase Expression

“…39 and 40). However, only the latter are concentrated at the neuromuscular synapse (41), where they are attached to the synaptic basal lamina (42)(43)(44)(45). Treatment of rat or mouse myotubes with CGRP results in a decrease in AChE expression (46 -48), whereas treatment of chicken myotubes with CGRP in one laboratory showed no change in the expression of catalytically active AChE while actually showing an increase in total AChE protein and mRNA (49,50).…”

Acetylcholinesterase of mammalian neuromuscular junctions: presence of tailed asymmetric acetylcholinesterase in synaptic basal lamina and sarcolemma.

“…There is indirect evidence, essentially from studies on electric fish AcChoEase, that the asymmetric forms of AcChoEase, which are composed of tetrameric protomers and a collagen-like multistranded tail (4)(5)(6)(7)(8), can interact with basal lamina components such as glycosaminoglycans of unknown nature (9), fibrous material (10), or fibronectin (11). In mammalian skeletal muscle, 16S AcChoEase has been found to be collagenase sensitive (12) and thus is probably homologous to the electric fish tailed enzyme.…”

Cholinesterases from flounder muscle

“…According to Bon et al [4] the molecular forms are divided into two principal classes. Asymmetric forms are composed of one, two or three catalytic tetramers linked by disulfide bridges to a collagen-like tail [5]. They are associated with mammalian neuromuscular junctions [6] and with synapses in the electric organ of Torpedo or electric eel [7,81.…”