Structure-activity relationships of scorpion alpha-neurotoxins: contribution of arginine residues.
The role of arginine residues in the structure-activity relationships of alpha-scorpion neurotoxins was studied. Toxins I and II from Androctonus australis Hector (north African scorpion), containing respectively 2 and 3 arginines, were modified by phenylglyoxal or p-hydroxyphenylglyoxal. Modified derivatives were purified by reverse-phase HPLC and/or ion exchange HPLC. Subsequent bioassays showed that toxin I (AaH I) derivatives with single modifications on Arg 2 and Arg 60 had low activity (25 and 14% of residual activity, assessed in receptor binding experiments). Doubly modified (Arg 2, Arg 60) AaH I had 7% residual activity while further derivatization of the alpha-amino group led to an almost inactive derivative. These results agree with the involvement of arginines 2 and 60, as well as the alpha-amino group, of AaH I in the toxin/receptor interaction, probably via electrostatic interactions. Consistent with the role of N-terminal residues, the selective removal of the N-terminal dipeptide Val-Arg of toxin III from the same scorpion resulted in low activity (7% residual activity). The arginine residue in position 56 of toxin II was important for bioactivity since the derivative modified by phenylglyoxal on Arg 56 exhibited low residual activity (20%). Arg 62 and Arg 18, on the other hand, can be modified without any great effect on the pharmacological activity of AaH II. These results furnish a more precise picture of those residues involved in the "toxic region", which appears to be composed of residues belonging to the conserved hydrophobic surface and to the C-terminal and N-terminal sequences.
Kharrat
R
R
CNRS URA 37-INSERM U 172 Laboratoire de Biochimie, Faculté de Médecine-Secteur Nord, Marseille, France.
Darbon
H
H
Granier
C
C
Rochat
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000378:metabolism; D007457:Iodine Radioisotopes; D007928:Lethal Dose 50; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity; D010658:Phenylglyoxal / Q000031:analogs & derivatives / Q000378:metabolism; D011487:Protein Conformation; D030162:Reptilian Proteins; D012604:Scorpion Venoms / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism; D014633:Valine
D007457:Iodine Radioisotopes; D009498:Neurotoxins; D030162:Reptilian Proteins; D012604:Scorpion Venoms; C065314:scorpion toxin I, Androctonus; C028465:4-hydroxyphenylglyoxal; C053969:scorpion toxin II, Androctonus; D001120:Arginine; D014357:Trypsin; D014633:Valine; D010658:Phenylglyoxal