Glycosylation of Acetylcholinesterase Forms in Microsomal Membranes from Normal and Dystrophic Lama2^dy Mouse Muscle

Abstract

Abstract:The distribution and glycosylation of acetyicholinesterase (AChE) forms in vesicles derived from sarcoplasmic reticulum of normal muscle (NMV) were investigated and compared with those from dystrophic muscle vesicles (DMV). AChE activity was similar in NMV and DMV. Most of the AChE in NMV and half in DMV were released with Triton X-1 00. Asymmetric (A 12) and globular hydrophilic and amphiphilic (G~, G~, G~, and G~) AChE species occurred in NMV and DMV, the lighter forms being predominant. The percentage of G~and G~de-creased in DMV. A fraction of the AChE that could not be extracted with detergent was detached with collagenase. Most of the detergent-released A12 AChE from NMV and nearly half in DMV failed to bind to Ricinus communis agglutinin (RCA-I). Conversely, the collagenase-detached isoforms bound to RCA, revealing that asymmetric AChE associated with internal membranes or basal lamina differed in glycosylation. Moreover, nearly half of GÃChE in DMV and a few in NMV bound to RCA. Most of the RCA-unreactive Gforms in NMV come from sarcolemma. The results indicate that dystrophy induces minor changes in the distribution and glycosylation of AChE forms in internal membranes of muscle.

Identification of inactive ecto‐5′‐nucleotidase in normal mouse muscle and its increased activity in dystrophic Lama2dy mice

“…In this context, it is worth noting that, at least in vitro, eNT binds laminin (Stochaj et al, 1989), the glycoprotein that is lacking in Lama2 dy mouse muscle. Despite the heterogeneity of eNT glycans , the enzyme from NM or DM binds to a similar extent with LCA, RCA and WGA, showing that, in contrast to acetylcholinesterase (Cabezas-Herrera et al, 1997), the glycosylation of eNT is not severely altered in DM. Moreover, the relative amount of the hydrophilic eNT dimers is not altered by dystrophy, revealing that the proteolysis of DM (Badalamente and Stracher, 2000) has no effect on eNT.…”

Post-translational modifications of proteins: Acetylcholinesterase as a model system

“…Differences in the distribution and glycosylation of AChE forms from the intracellular membranes have been also shown when muscles of normal and Lama2(dy) dystrophic mice were compared [77]. However, the lack of differences in the interaction of lectins with homologous AChE forms in the brain of normal and Lama2 mice indicates that, in contrast to AChE forms in skeletal muscle, this pathological condition does not disturb the processing of the oligosaccarides of the brain enzyme forms [78].…”

The levels of both lipid rafts and raft-located acetylcholinesterase dimers increase in muscle of mice with muscular dystrophy by merosin deficiency

“…AChE-T is by far the major and the most physiologically relevant subunit in mammalian brain and muscle. In muscle, AChE-T polymerizes into globular (G 1 , G 2 and G 4 ) and asymmetric (A 4 , A 8 and A 12 ) forms, which, after appropriate processing, reach specific cell stores [11,12]. The asymmetric species are the principal if not the only AChE forms in the neuromuscular junction (NMJ) of fast-twitch muscle [13].…”

“…given the abnormal pattern of AChE forms in merosin-deficient muscle [11] and the capacity of AChE to bind laminin, caveolin and other protein partners [19][20][21] it might be that the merosin deficiency disrupted AChE transport toward the surface membrane of muscle.…”

“…Cholinesterase (ChE) activity in the gradient fractions was assayed by the Ellman method [11]; AChE with 1 mM acetylthiocholine plus 50 µM Iso-OMPA and BuChE with 1 mM butyrylthiocholine plus 10 µM BW284c51. Inhibition of BuChE activity by Triton X-100 was relieved by adding 0.5% Brij 96 to the assay mixture.…”