Interactions between lectins and acetylcholinesterase from the sarcotubular system of skeletal muscle

Abstract

The oligosaccharide chains attached to the multiple forms of acetylcholinesterase (AChE) in a fraction enriched in membranes of the sarcoplasmic reticulum and T-tubules of rabbit skeletal muscle were studied using lectins. By sequential extraction of the membranes with Triton X-100, two preparations of soluble enzyme were obtained, S(1) and S(2). Monomeric, tetrameric and asymmetric forms of AChE are present, and all of these bind to concanavalin A, yielding heavy aggregates with no loss of enzyme activity. The interaction of AChE with lectins suggests that the carbohydrate residues are N-linked to the protein backbone. The extent of the association of isolated AChE forms with wheatgerm and Ricinus communis agglutinins was variable, but grew as the molecular complexity increased. The interaction of monomeric AChE, in S(1) and S(2), with concanavalin A and Lens culinaris agglutinin suggests heterogeneity in the oligosaccharide moieties of this single form. Antibodies of the HNK-1 anti-carbohydrate type show no reaction with any of the AChE forms. Sialylation also appeared to be absent. The results overall indicate that some monomeric forms of AChE are fucosylated in the Golgi system to become precursors of tetrameric and asymmetric components of this enzyme in muscle.