Roles of the aromatic residues in cobrotoxin in antigenicity and binding activity to nicotinic acetylcholine receptor.
The single Trp-29 in cobrotoxin was modified with 2-hydroxy-5-nitrobenzyl bromide, and Tyr-25 and -35, with tetranitromethane. Although the binding activity of cobrotoxin to the nicotinic acetylcholine receptor (nAChR) was decreased after modification of Trp-29, the antigenicity remained essentially unchanged as measured by a competitive RIA. Tyr-35-nitrated cobrotoxin still retained relatively high antigenicity and potent binding activity to nAChR. However, modification of both Tyr-25 and Tyr-35 led to an altered secondary structure, with greatly reduced binding to antibody and receptor. Hence, Tyr-25 in cobrotoxin is essential for the maintenance of the active conformation for the bindings. Although the non-precipitating antibody against cobrotoxin exhibiting a higher neutralizing capacity than did the precipitating antibody, the binding affinity of the former to cobrotoxin and its modified derivatives was lower than that of the latter.
Kuo
K W
KW
Department of Biochemistry, Kaohsiung Medical College, Taiwan, R.O.C.
Chang
C C
CC
D000818:Animals; D001665:Binding Sites; D003039:Cobra Neurotoxin Proteins / Q000276:immunology* / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D009500:Neutralization Tests; D011233:Precipitin Tests; D011485:Protein Binding; D011487:Protein Conformation; D011863:Radioimmunoassay; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014443:Tyrosine / Q000502:physiology
D003039:Cobra Neurotoxin Proteins; D000939:Epitopes; D011978:Receptors, Nicotinic; D014443:Tyrosine