Rescue and Stabilization of Acetylcholinesterase in Skeletal Muscle by N-terminal Peptides Derived from the Noncatalytic Subunits

The NMJ as a model synapse: New perspectives on formation, synaptic transmission and maintenance: Acetylcholinesterase at the neuromuscular junction

Acetylcholinesterase (AChE) is an essential enzymatic component of the neuromuscular junction where it is responsible for terminating neurotransmission by the cholinergic motor neurons. The enzyme at the neuromuscular junction (NMJ) is contributed primarily by the skeletal muscle where it is produced at higher levels in the post-synaptic region of the fibers. The major form of AChE at the NMJ is a large asymmetric form consisting of three tetramers covalently attached to a three-stranded collagen-like tail which is responsible for anchoring it to the synaptic basal lamina. Its location and expression is regulated to a large extent by the motor neurons and occurs at the transcriptional, translational and post-translational levels. While its expression can be quite rapid in tissue cultured cells, its half-life in vivo appears to be quite long, about three weeks, although more rapidly turning over pools have been described. Finally the essential nature of this enzyme is underscored by the fact that no naturally occurring null mutations of the catalytic subunit have been described in higher organisms and the few dozen humans carrying mutations in the collagen tail responsible for anchoring the enzyme at the NMJ are severely affected.

Diagnoses of Pathological States Based on Acetylcholinesterase and Butyrylcholinesterase

Two cholinesterases exist: Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). While AChE plays a crucial role in neurotransmissions, BChE has no specific function apart from the detoxification of some drugs and secondary metabolites from plants. Thus, both AChE and BChE can serve as biochemical markers of various pathologies. Poisoning by nerve agents like sarin, soman, tabun, VX, novichok and overdosing by drugs used in some neurodegenerative disorders like Alzheimer´s disease and myasthenia gravis, as well as poisoning by organophosphorus pesticides are relevant to this issue. But it appears that changes in these enzymes take place in other processes including oxidative stress, inflammation, some types of cancer and genetically conditioned diseases. In this review, the cholinesterases are introduced, the mechanism of inhibitors action is explained and the relations between the cholinesterases and pathologies are explained.

Polyproline-rich peptides associated with Torpedo californica acetylcholinesterase tetramers

Acetylcholinesterase (AChE) terminates cholinergic neurotransmission by hydrolyzing acetylcholine. The collagen-tailed AChE tetramer is a product of 2 genes, ACHE and ColQ. The AChE tetramer consists of 4 identical AChE subunits and one polyproline-rich peptide, whose function is to hold the 4 AChE subunits together. Our goal was to determine the amino acid sequence of the polyproline-rich peptide(s) in Torpedo californica AChE (TcAChE) tetramers to aid in the analysis of images that will be acquired by cryo-EM. Collagen-tailed AChE was solubilized from Torpedo californica electric organ, converted to 300 kDa tetramers by digestion with trypsin, and purified by affinity chromatography. Polyproline-rich peptides were released by denaturing the TcAChE tetramers in a boiling water bath, and reducing disulfide bonds with dithiothreitol. Carbamidomethylated peptides were separated from TcAChE protein on a spin filter before they were analyzed by liquid chromatography tandem mass spectrometry on a high resolution Orbitrap Fusion Lumos mass spectrometer. Of the 64 identified collagen-tail (ColQ) peptides, 60 were from the polyproline-rich region near the N-terminus of ColQ. The most abundant proline-rich peptides were SVNKCCLLTPPPPPMFPPPFFTETNILQE, at 40% of total mass-spectral signal intensity, and SVNKCCLLTPPPPPMFPPPFFTETNILQEVDLNNLPLEIKPTEPSCK, at 27% of total intensity. The high abundance of these 2 peptides makes them candidates for the principal form of the polyproline-rich peptide in the trypsin-treated TcAChE tetramers.

Biogenesis, assembly and trafficking of acetylcholinesterase

Acetylcholinesterase (AChE) is expressed as several homomeric and heterooligomeric forms in a wide variety of tissues such as neurons in the central and peripheral nervous systems and their targets including skeletal muscle, endocrine and exocrine glands. In addition, glycolipid-anchored forms are expressed in erythropoietic and lymphopoietic cells. While transcriptional and post-transcriptional regulation is important for determining which AChE oligomeric forms are expressed in a given tissue, translational and post-translational regulatory mechanisms at the level of protein folding, assembly and sorting play equally important roles in assuring that the AChE molecules reach their intended sites on the cell surface in the appropriate numbers. This brief review will focus on the latter events in the cell with the goal of providing novel therapeutic interventional strategies for the treatment of organophosphate and carbamate pesticide and nerve agent exposure. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

The C5 Variant of the Butyrylcholinesterase Tetramer Includes a Noncovalently Bound 60 kDa Lamellipodin Fragment

Humans with the C5 genetic variant of butyrylcholinesterase (BChE) have 30–200% higher plasma BChE activity, low body weight, and shorter duration of action of the muscle relaxant succinylcholine. The C5 variant has an extra, slow-moving band of BChE activity on native polyacrylamide gel electrophoresis. This band is about 60 kDa larger than wild-type BChE. Umbilical cord BChE in 100% of newborn babies has a C5-like band. Our goal was to identify the unknown, 60 kDa protein in C5. Both wild-type and C5 BChE are under the genetic control of two independent loci, the BCHE gene on Chr 3q26.1 and the RAPH1 (lamellipodin) gene on Chr 2q33. Wild-type BChE tetramers are assembled around a 3 kDa polyproline peptide from lamellipodin. Western blot of boiled C5 and cord BChE showed a positive response with an antibody to the C-terminus of lamellipodin. The C-terminal exon of lamellipodin is about 60 kDa including an N-terminal polyproline. We propose that the unknown protein in C5 and cord BChE is encoded by the last exon of the RAPH1 gene. In 90% of the population, the 60 kDa fragment is shortened to 3 kDa during maturation to adulthood, leaving only 10% of adults with C5 BChE.