The isolation and characterisation of the nicotinic acetylcholine receptor from human skeletal muscle

Nicotinic acetylcholine receptor protein has been purified from human skeletal muscle by a procedure involving extraction in non-ionic detergent followed by affinity purification on immobilised alpha-toxin. Purified receptor preparations had specific activities of 0.5-3.5 mumol alpha-bungarotoxin binding sites/g protein and sedimented as a single 125I-alpha-bungarotoxin-binding species in sucrose-density-gradient centrifugation with s20,w = 9.5 S. The purified protein focussed as a single sharp band at pH 5.1 when complexed to 125I-alpha-bungarotoxin. Polyacrylamide gel electrophoresis of the purified receptor under denaturing conditions showed two major protein bands with Mr 42 000 and 66 000 respectively with the occasional appearance of minor components of Mr 56 000 and 85 000. Only the 42 000-Mr band was labelled with the affinity reagent, 4-(N-maleimido)[3H]-benzyltrimethylammonium. The purified receptor bound 125I-alpha-bungarotoxin and d-tubocurarine with Kd values of 0.5 nM and 0.25 microM respectively. It behaved similarly to unpurified detergent-extracted human receptor in the radioimmunoassay for anti-(human acetylcholine receptor) antibodies and when injected into rabbits caused increased levels of the latter antibodies but did not cause experimental autoimmune myasthenia gravis.