Importance of the conserved aromatic residues in the scorpion alpha-like toxin BmK M1: the hydrophobic surface region revisited.
About one-third of the amino acid residues conserved in all scorpion long chain Na+ channel toxins are aromatic residues, some of which constitute the so-called "conserved hydrophobic surface." At present, in-depth structure-function studies of these aromatic residues using site-directed mutagenesis are still rare. In this study, an effective yeast expression system was used to study the role of seven conserved aromatic residues (Tyr5, Tyr14, Tyr21, Tyr35, Trp38, Tyr42, and Trp47) from the scorpion toxin BmK M1. Using site-directed mutagenesis, all of these aromatic residues were individually substituted with Gly in association with a more conservative substitution of Phe for Tyr5, Tyr14, Tyr35, or Trp47. The mutants, which were expressed in Saccharomyces cerevisiae S-78 cells, were then subjected to a bioassay in mice, electrophysiological characterization on cloned Na+ channels (Nav1.5), and CD analysis. Our results show an eye-catching correlation between the LD50 values in mice and the EC50 values on Nav1.5 channels in oocytes, indicating large mutant-dependent differences that emphasize important specific roles for the conserved aromatic residues in BmK M1. The aromatic side chains of the Tyr5, Tyr35, and Trp47 cluster protruding from the three-stranded beta-sheet seem to be essential for the structure and function of the toxin. Trp38 and Tyr42 (located in the beta2-sheet and in the loop between the beta2- and beta3-sheets, respectively) are most likely involved in the pharmacological function of the toxin.
Sun
Yan-Mei
YM
Center for Molecular Biology, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, People's Republic of China.
Bosmans
Frank
F
Zhu
Rong-Huan
RH
Goudet
Cyril
C
Xiong
Yu-Mei
YM
Tytgat
Jan
J
Wang
Da-Cheng
DC
D000595:Amino Acid Sequence; D024322:Amino Acids, Aromatic / Q000502:physiology*; D000818:Animals; D002942:Circular Dichroism; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000502:physiology*; D004594:Electrophysiology; D019476:Insect Proteins; D051379:Mice; D009498:Neurotoxins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D009865:Oocytes; D017354:Point Mutation; D012604:Scorpion Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D012605:Scorpions / Q000737:chemistry*; D015222:Sodium Channels / Q000187:drug effects; D013329:Structure-Activity Relationship; D014981:Xenopus
D024322:Amino Acids, Aromatic; C403888:BmK M1 neurotoxin; D019476:Insect Proteins; D009498:Neurotoxins; D012604:Scorpion Venoms; D015222:Sodium Channels