Scorpion toxins from Buthus martensii Karsch all possess a predicted alpha-tight-turn.
We have purified a new toxin (BmK 17[4]) from Asian scorpion (Buthus martensii Karsch) venom that possesses a distinctive structural motif in its N-terminal (positions 8-12) that is similarly found in two other previously described alpha-like toxins. BmK 17[4] prolongs action potentials (APs) in frog nerve and was purified using gel filtration, ion exchange, fast protein liquid chromatography (FPLC), and high-performance liquid chromatography (HPLC). BmK 17[4] significantly prolonged frog APs but it did not alter APs from an insect ventral nerve cord at similar doses. When applied to voltage-clamped frog muscle single fibers, BmK 17[4] prolonged fast inactivation. Because the polypeptide prolongs APs when both K+ and Ca2+ channels were blocked, BMK 17[4] acts to selectively alter Na+ channel inactivation. The N-terminal sequence of BmK 17[4] was found to be VRDAYIAKPENCVYXC --. The molar mass of BmK 17[4] was determined by LC/MS/MS to be 7097 Daltons. The N- terminal motif (KPENC), which introduces a reverse turn in residues 8-12, does not appear in previously characterized BmK alpha-toxins and may be characteristic of alpha-like toxins. Sequence similarity database searches were used to test whether the N-terminal sequences of alpha-like polypeptide toxins from B. martensii Karsch possess a distinctive structural motif in its 5-residue reverse turn (alpha-turn) that is conserved. Sequence similarities with putative polypeptides encoded by cDNAs obtained from a cDNA library [Zhu, S. Y., Li, W. X., Zenq, X. C., et al. (2000) Nine novel precursors of Buthus martensii scorpiox alpha-toxin homologues. Toxicon 38, 1653-1661] from BmK venom glands showed that an active polypeptide toxin cleaved from the putative propolypeptide toxin BmK M9 is likely identical to BmK 17[4]. Sequence comparisons with toxins and putative toxins from B. martensii Karsch and other species revealed that a group of these toxins possess a common structural motif in their alpha-turn. A neighbor-joining phylogenetic analysis suggests that there are two phylogenetic sister groups of related BmK polypeptides; one possesses the KPENC motif and the other possesses a modifed version (KPHNC) of it.
Hahin
Richard
R
Biological Sciences, Northern Illinois University, DeKalb, IL 60115, USA. hahin@niu.edu
Chen
Ziyi
Z
Wang
Danhui
D
Reddy
Giridher
G
Mao
Long
L
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002412:Cations; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D019992:Databases as Topic; D007313:Insecta; D018402:Manduca / Q000378:metabolism; D008969:Molecular Sequence Data; D009420:Nervous System / Q000187:drug effects; D009474:Neurons / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D010802:Phylogeny; D011392:Proline / Q000737:chemistry; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000302:isolation & purification; D012605:Scorpions; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism; D013997:Time Factors
D002412:Cations; D010455:Peptides; D012604:Scorpion Venoms; D015222:Sodium Channels; D011392:Proline; D012964:Sodium