Structural and functional organization of synaptic acetylcholinesterase

The expression of the synaptic asymmetric form of the enzyme acetylcholinesterase (ACNE) depends of two different genes: the gene that encodes for the catalytic subunit and the gene that encodes for the collagenic tail, ColQ. Asymmetric ACNE is specifically localized to the basal lamina at the neuromuscular junction (NMJ). This highly organized distribution pattern suggests the existence of one or more specific binding sites in ColQ required for its anchorage to the synaptic basal lamina. Recent evidence support this notion: first, the presence of two heparin-binding domains in ColQ that interact with heparan sulfate proteoglycans (HSPGs) at the synaptic basal lamina; and second, a knockout mouse for perlecan, a HSPG concentrated in nerve-muscle contact, in which absence of asymmetric ACNE at the NMJ is observed. The physiological importance of collagen-tailed ACNE form in skeletal muscle has been illustrated by the identification of several mutations in the ColQ gene. These mutations determine end-plate acetylcholinesterase deficiency and induce one type of synaptic functional disorders observed in Congenital Myasthenic Syndromes (CMSs). (C) 2004 Elsevier B.V All rights reserved.