Isolation of the heparan sulfate proteoglycans from the extracellular matrix of rat skeletal muscle

Abstract

We have previously shown that asymmetric collagen‐tailed acetylcholinesterase (AChE) is anchored to the extracellular matrix (ECM) by heparan sulfate proteoglycans (HSPGs). Here we present our studies on the characterization of such PGs from the ECM of rat skeletal muscles. After radiolabling with ³⁵SO₄ for 24 h, PGs were extracted from the muscle ECM with 4.0 M guanidine‐HCl containing protease inhibitors. PGs were subsequently isolated using sequential DEAE‐Sephacel chromatography, digestion with chondroitinase ABC, and Sepharose CL‐4B. Two different hydrodynamic size species of HSPGs were found. One type had a Mr of 4–6 × 10⁵ (Kav = 0.25) as estimated by gel chromatography in the presence of 1% SDS and accounted for 75% of the total HSPGs. The other HSPG had a Mr 1.5–2.5 × 10⁵ (Kav = 0.41). The glycosaminoglycan (GAG) side chains (Mr 20,000 and 12,000) were found composed only of heparan sulfate as determined by nitrous acid oxidation and heparitinase treatment. The large‐sized HSPG, which is concentrated in synaptic regions, contains only GAG chains of Mr 20,000, suggesting that each HSPG contains only one kind of heparan sulfate chain in its structure. Our results definitively establish by biochemical criteria that the basement membrane of mammalian skeletal muscle contains HSPGs, the likely matrix receptor for the immobilization of the asymmetric collagen‐tailed AChE at the neuromuscular junction.