Structural basis for the voltage-gated Na+ channel selectivity of the scorpion alpha-like toxin BmK M1.
Scorpion alpha-like toxins are proteins that act on mammalian and insect voltage-gated Na+ channels. Therefore, these toxins constitute an excellent target for examining the foundations that underlie their target specificity. With this motive we dissected the role of six critical amino acids located in the five-residue reverse turn (RT) and C-tail (CT) of the scorpion alpha-like toxin BmK M1. These residues were individually substituted resulting in 11 mutants and were subjected to a bioassay on mice, an electrophysiological characterization on three cloned voltage-gated Na+ channels (Nav1.2, Nav1.5 and para), a CD analysis and X-ray crystallography. The results reveal two molecular sites, a couplet of residues (8-9) in the RT and a hydrophobic surface consisting of residues 57 and 59-61 in the CT, where the substitution with specific residues can redirect the alpha-like characteristics of BmK M1 to either total insect or much higher mammal specificity. Crystal structures reveal that the pharmacological ramification of these mutants is accompanied by the reshaping of the 3D structure surrounding position 8. Furthermore, our results also reveal that residues 57 and 59-61, located at the CT, enclose the critical residue 58 in order to form a hydrophobic "gasket". Mutants of BmK M1 that interrupt this hydrophobic surface significantly gain insect selectivity.
Ye
Xiang
X
Center for Structural and Molecular Biology, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, People's Republic of China.
Bosmans
Frank
F
Li
Chong
C
Zhang
Ying
Y
Wang
Da-Cheng
DC
Tytgat
Jan
J
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002942:Circular Dichroism; D017124:Conserved Sequence / Q000502:physiology; D018360:Crystallography, X-Ray; D004594:Electrophysiology; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D007313:Insecta / Q000187:drug effects; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D062551:NAV1.2 Voltage-Gated Sodium Channel; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009498:Neurotoxins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology; D011487:Protein Conformation; D012604:Scorpion Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D012605:Scorpions / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
C403888:BmK M1 neurotoxin; D019476:Insect Proteins; D009124:Muscle Proteins; D062551:NAV1.2 Voltage-Gated Sodium Channel; D062554:NAV1.5 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D009498:Neurotoxins; C568251:SCN2A protein, human; C568320:SCN5A protein, human; C000654500:Scn2a protein, mouse; C568321:Scn5a protein, mouse; D012604:Scorpion Venoms; D015222:Sodium Channels