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Crystal Structure Of Mutant K8A Of Scorpion alpha-Like Neurotoxin Bmk M1 From Buthus Martensii Karsch
Structural highlights
FunctionSCM1_MESMA Alpha toxins bind voltage-independently at site-3 of sodium channels (Nav) and inhibit the inactivation of the activated channels thereby blocking neuronal transmission. This toxin is active against both mammals and insects, and is classified as an alpha-like toxin. It is active on Nav1.2/SCN2A (EC(50)=139-252 nM), Nav1.3/SCN3A (EC(50)=565 nM), Nav1.4/SCN4A and Nav1.5/SCN5A (EC(50)=195-500 nM), Nav1.6/SCN8A (EC(50)=214 nM), and drosophila DmNav1 (EC(50)=30 nM) (PubMed:11322948, PubMed:12705833, PubMed:15677695, PubMed:19162162, PubMed:20678086). In mNav1.6/SCN8A, the toxin induces a large increase in both transient and persistent currents, which correlates with a prominent reduction in the fast component of inactivating current (PubMed:20678086). In rNav1.2/SCN2A and rNav1.3/SCN3A, toxin-increased currents is much smaller (PubMed:19162162, PubMed:20678086). Moreover, the toxin only accelerates the slow inactivation development and delay recovery of mNav1.6/SCN8A through binding to the channel in the open state (PubMed:20678086). Is 6-fold more toxic than BmK-M2. In vivo, intrahippocampal injection into rat induces epileptiform responses (PubMed:16229835). In addition, intraplantar injection into rat induces spontaneous nociception and hyperalgesia (PubMed:14554105).[1] [2] [3] [4] [5] [6] [7] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedScorpion 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. Structural basis for the voltage-gated Na+ channel selectivity of the scorpion alpha-like toxin BmK M1.,Ye X, Bosmans F, Li C, Zhang Y, Wang DC, Tytgat J J Mol Biol. 2005 Nov 4;353(4):788-803. Epub 2005 Sep 22. PMID:16209876[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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