Linkage of the acetylcholine transporter-vesamicol receptor to proteoglycan synaptic vesicles

Abstract

The relationship of the acetylcholine transporter-vesamicol receptor (AcChT-VR) to proteoglycan in Torpedo electric organ synaptic vesicles was investigated. The cholate-solubilized VR was immunoprecipitated by a monoclonal antibody directed against the SV1 epitope located in the glycosaminoglycan portion of the proteoglycan. AcChT that was photoaffinity-labeled with a tritiated high-affinity analogue of AcCh [cyclohexylmethyl cis-N-(4-azidophenacyl)-N-methylisonipecotate] and then denatured in sodium dodecyl sulfate also immunoprecipitated. The labeled AcChT exhibited a M(r) range of 100,000-200,000. Proteoglycan did not engage in detectable nonspecific reversible aggregation that might mask the presence of another subunit during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In vesicles permeabilized with cholate, the enzymes keratanase and testicular hyaluronidase inactivated binding of vesamicol and destroyed the SV1 epitope without detectable proteolysis. Other glycosaminoglycan-degrading enzymes were without effect. The results demonstrate that the AcChT-VR and proteoglycan are very strongly linked and that glycosaminoglycan-like polysaccharide controls the conformation of the VR. The unexpected linkage to proteoglycan suggests that AcChT-VR in intact terminals might communicate with extracellular matrix and participate in stabilization and operation of the synapse.

Claustrin, an antiadhesive neural keratan sulfate proteoglycan, is structurally related to MAP1B

“…Our demonstration of homology between claustrin to the ENP 1 protein found in Torpedo electromotor neurons is interesting in light of recent evidence identifying a KSPG associated with the synaptic vesicles of Torpedo electric organ (Bahr et al, 1992). The partial Torpedo cDNA clone for ENP 1 is 70% homologous to the 5' region of the mouse MAP 1 B sequence, and appears to also represent a 5' truncated fragment of MAP 1 B (Ngsee and Scheller, 1989).…”

“…Several proteoglycans associated with synaptic vesicles and membranes in Torpedo have been characterized (Kiene and Stadler, 1987;Carlson and Wight, 1987). Recently, it has been reported that the acetylcholine transporter-vesamicol receptor complex ( AcChT-VR) of Torpedo synaptic vesicles is associated with a KSPG (Bahr et al, 1992). Although the exact identity of this KSPG has not been determined, it may be related to the cholinergic synaptic vesicle proteogiycan ( SVPG) previously described (Stadler and Dowe, 1982;Carlson and Kelly, 1983 ).…”

Selective Loss of Cerebral Keratan Sulfate in Alzheimer's Disease

“…It is therefore of interest that a neuron-specific KS-substituted protein has been demonstrated in the Torpedo electric organ and in rat brain (13). This protein ("synaptoglycan" (4)) is located intracellularly in synaptic vesicles and has been implicated with the transport of acetylcholine (14). Conceivably, binding of the positively charged neurotransmitter to highly sulfated regions of KS may be critical to normal transport, which thus would be perturbed in AD.…”

Heparin modulates the single channel kinetics of reconstituted AMPA receptors from rat brain

“…Most pertinent are specific proteoglycans that have been shown to be involved in the mechanisms of neurotransmission (Bahr et al, 1992a) as well as in the formation and maintenance of neuromuscular junctions (Nastuk and Fallon, 1993). This broad spectrum of action may complicate the interpretations concerning the effects of heparin on AMPA receptors in intact preparations.…”

“…With the overall finding that heparin binds to and alters the properties of AMPA receptors, it is of interest that glycosaminoglycan-containing proteoglycans are abundant in the brain (Herndon and Lander, 1990) and are known to have effects on a large number of physiological processes (see Ruoslahti, 1989). Most pertinent are specific proteoglycans that have been shown to be involved in the mechanisms of neurotransmission (Bahr et al, 1992a) as well as in the formation and maintenance of neuromuscular junctions (Nastuk and Fallon, 1993). This broad spectrum of action may complicate the interpretations concerning the effects of heparin on AMPA receptors in intact preparations.…”