Two Different Heparin-binding Domains in the Triple-helical Domain of ColQ, the Collagen Tail Subunit of Synaptic Acetylcholinesterase

Abstract

ColQ, the collagen tail subunit of asymmetric acetylcholinesterase, is responsible for anchoring the enzyme at the vertebrate synaptic basal lamina by interacting with heparan sulfate proteoglycans. To get insights about this function, the interaction of ColQ with heparin was analyzed. For this, heparin affinity chromatography of the complete oligomeric enzyme carrying different mutations in ColQ was performed. Results demonstrate that only the two predicted heparin-binding domains present in the collagen domain of ColQ are responsible for heparin interaction. Despite their similarity in basic charge distribution, each heparin-binding domain had different affinity for heparin. This difference is not solely determined by the number or nature of the basic residues conforming each site, but rather depends critically on local structural features of the triple helix, which can be influenced even by distant regions within ColQ. Thus, ColQ possesses two heparinbinding domains with different properties that may have non-redundant functions. We hypothesize that these binding sites coordinate acetylcholinesterase positioning within the organized architecture of the neuromuscular junction basal lamina.At vertebrate cholinergic synapses, acetylcholinesterase (AChE) 1 rapidly hydrolyzes the neurotransmitter acetylcholine, thereby terminating synaptic transmission. This key function does not only require a high catalytic turnover number but also a strategic positioning of the enzyme. This is achieved by the association of AChE catalytic subunits with structural subunits that bring them to the site of action. In the case of asymmetric AChE, the collagen ColQ is responsible for the localization of the enzyme at the vertebrate neuromuscular junction. Inactivation of the ColQ gene in mice or mutations in the human ColQ gene result in the absence of enzyme accumulation at the neuromuscular junction and are the cause of a congenital myasthenic syndrome (type 1c) (1, 2).As found in other collagens, ColQ contains a central triplehelical domain surrounded by non-collagenous N-and C-terminal domains (Fig. 1A). Each N-terminal domain organizes an AChE tetramer, so the triple-helical structure generates an A 12 or asymmetric AChE form with 12 catalytic subunits (3, 4). The collagen domain is characterized by Gly-Xaa-Yaa repeats and a high proportion of the stabilizing proline and hydroxyproline residues. The C-terminal domain is divided into a proline-rich region, important for triple-helix formation (5), and a cysteinerich region probably involved in the anchorage of AChE at the neuromuscular junction, since mutations in this region prevent the accumulation of AChE in congenital myasthenic syndrome type 1c patients (2).Heparan sulfate proteoglycans (HSPGs) have been implicated in the anchorage of asymmetric AChE to the synaptic basal lamina by interacting with ColQ through their heparan sulfate (HS) chains. This was proposed after showing that AChE could be specifically solubilized from the tissue with heparinase as well as with HS and ...

Silencing SMYD3 in hepatoma demethylates RIZI promoter induces apoptosis and inhibits cell proliferation and migration

“…SMYD3 also upregulates genes linked to cell adhesion and invasion, such as ITGA5 [21] , COLQ [22] , SELL [23] , NEURL [24] , and PECAM1 [25] , which may be responsible for cell migration regulator y role of SMYD3 in our experiment. To investigate whether SMYD3 might act on HCC oncological activity through TSG inactivation, we examined if RIZ1 activity could be regulated by SMYD3 in different hepatoma cells.…”

ColQ Controls Postsynaptic Differentiation at the Neuromuscular Junction

“…The GFP-ColQ-Y431S cDNA clone has been previously described by Cartaud et al (2004). The GFP-ColQ-⌬Ct and GFP-ColQ-⌬Col cDNA clones were generated from ⌬Ct and ⌬Col constructs described by Deprez et al (2003) in which the GFP tag sequence was introduced at the same position as for GFP-ColQ construct. The GFP-ColQ-⌬Col⌬Ct cDNA clone was generated by inserting four stop codons in the GFP-ColQ-⌬Col construct after the ColQ trimerization domain (amino acid 370).…”

Anti-MuSK autoantibodies block binding of collagen Q to MuSK

“…First, MuSK-IgG does not block binding of ColQtailed AChE to the NMJ to a detectable extent in the patients. ColQ is localized to the synaptic basal lamina via 2 mechanisms: one is by binding to heparin sulfate proteoglycans including perlecan, 7,8 and the other is by binding to MuSK. 9 We previously reported that both mechanisms are required for in vitro anchoring of human ColQ to the frog NMJ.…”

“…domain of ColQ 7 bind to heparin sulfate proteoglycans, such as perlecan 8 ; and the C-terminal domain of ColQ binds to MuSK. 9 Five percent to 15% of patients with myasthenia gravis (MG) carry antibodies against MuSK (MuSK-immunoglobulin G [IgG]).…”