Differential contribution of the conserved tyrosine residues to activity and structural stability of Ophiophagus hannah alpha-neurotoxins.
Two alpha-neurotoxins, Oh-4 and Oh-7, from king cobra (Ophiophagus hannah) venom were subjected to Tyr modification with tetranitromethane. Selective nitration of Tyr4 in Oh-4 caused a slight decrease in lethal toxicity of 11% and a decrease in nicotinic acetylcholine receptor (nAchR)-binding activity of 28%, whereas nitration of Tyr4 in Oh-7 resulted in an approximately equal 60% decrease in lethality and nAchR-binding activity. When the Tyr23 in Oh-4 or Tyr22 in Oh-7 appears to be 'buried' in the toxin following further modification, the toxins lost their biological activity and conformational change concurrently. Nevertheless, the dinitrated Oh-4 retained a beta-sheet structure as revealed by CD spectra and exhibited a precipitin reaction with anti-Oh-4 sera. These results indicate that both Tyr4 and Tyr22 play a crucial role in the neurotoxicity of Oh-7, whereas intact Tyr23 is involved in the manifestation of the toxicity of Oh-4 to a greater extent. In contrast to Oh-4, the conformational stability of Oh-7 depends heavily upon the integrity of Tyr22.
Chang
L
L
Institute of Biomedical Sciences, National Sun Yat-Sen University, Kaohsiung, Taiwan. lschang@mail.nsysu.edu.tw
Chang
C
C
Lin
S
S
D002942:Circular Dichroism; D004546:Elapid Venoms / Q000737:chemistry*; D005779:Immunodiffusion; D009498:Neurotoxins / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011978:Receptors, Nicotinic / Q000378:metabolism; D013774:Tetranitromethane / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry*
D004546:Elapid Venoms; D009498:Neurotoxins; D011978:Receptors, Nicotinic; D014443:Tyrosine; D013774:Tetranitromethane