title: Activation of skeletal ryanodine receptors by two novel scorpion toxins from Buthotus judaicus.
abstract: Buthotus judaicus toxin 1 (BjTx-1) and toxin 2 (BjTx-2), two novel peptide activators of ryanodine receptors (RyR), were purified from the venom of the scorpion B. judaicus. Their amino acid sequences differ only in 1 residue out of 28 (residue 16 corresponds to Lys in BjTx-1 and Ile in BjTx-2). Despite a slight difference in EC(50), both toxins increased binding of [(3)H]ryanodine to skeletal sarcoplasmic reticulum at micromolar concentrations but had no effect on cardiac or liver microsomes. Their activating effect was Ca(2+)-dependent and was synergized by caffeine. B. judaicus toxins also increased binding of [(3)H]ryanodine to the purified RyR1, suggesting that a direct protein-protein interaction mediates the effect of the peptides. BjTx-1 and BjTx-2 induced Ca(2+) release from Ca(2+)-loaded sarcoplasmic reticulum vesicles in a dose-dependent manner and induced the appearance of long lived subconductance states in skeletal RyRs reconstituted into lipid bilayers. Three-dimensional structural modeling reveals that a cluster of positively charged residues (Lys(11) to Lys(16)) is a prominent structural motif of both toxins. A similar structural motif is believed to be important for activation of RyRs by imperatoxin A (IpTx(a)), another RyR-activating peptide (Gurrola, G. B., Arevalo, C., Sreekumar, R., Lokuta, A. J., Walker, J. W., and Valdivia, H. H. (1999) J. Biol. Chem. 274, 7879-7886). Thus, it is likely that B. judaicus toxins and imperatoxin A bind to RyRs by means of electrostatic interactions that lead to massive conformational changes in the channel protein. The different affinity and structural diversity of this family of scorpion peptides makes them excellent peptide probes to identify RyR domains that trigger the channel to open.
authors.affiliation: Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA. xzhu@bics.bwh.harvard.edu
authors.forename: Xinsheng
authors.initials: X
authors.lastname: Zhu
authors.forename: Fernando Z
authors.initials: FZ
authors.lastname: Zamudio
authors.forename: Beth A
authors.initials: BA
authors.lastname: Olbinski
authors.forename: Lourival D
authors.initials: LD
authors.lastname: Possani
authors.forename: Héctor H
authors.initials: HH
authors.lastname: Valdivia
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D008051:Lipid Bilayers / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D009498:Neurotoxins / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D012433:Ryanodine / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D012605:Scorpions; D012984:Software; D013053:Spectrophotometry; D055672:Static Electricity; D013552:Swine; D013997:Time Factors
chemical_list: C487824:Buthotus judaicus toxin 1; C487825:Buthotus judaicus toxin 2; D008051:Lipid Bilayers; D009498:Neurotoxins; D010455:Peptides; D019837:Ryanodine Receptor Calcium Release Channel; D012604:Scorpion Venoms; C105361:imperatoxin A; D012433:Ryanodine; D002110:Caffeine; D008239:Lysine; D002118:Calcium