Tong Xiaotian, Zhu Jing, Ma Yuguang, Chen Xiang, Wu Gong, He Fahu, Cao Chunyang, Wu Houming
State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China.
Biochemistry. 2007 Oct 9;46(40):11322-30. doi: 10.1021/bi7006788. Epub 2007 Sep 18.
The solution structure of an alpha-insect toxin from Buthus martensii Karsch, BmKalphaIT01, has been determined by two-dimensional NMR spectroscopy and molecular modeling techniques. Combining the sequence homology comparison and toxicity bioassays, BmKalphaIT01 has been suggested to be a natural mutant of alpha-insect toxins and so can serve as a tool to study the relationship of structure-function among this group of toxins. The overall structure of BmKalphaIT01 shares a common core structure consisting of an alpha-helix packed against a three-stranded antiparallel beta-sheet, which exhibits distinctive local conformations within the loops connecting these secondary structure elements. The solution structure of BmKalphaIT01 features a non-proline cis peptide bond between Asn9 and Tyr10, which is proposed to mediate the spatial closing of the five-residue turn (Gln8-Cys12) and the C-terminal segment (Arg58-His64) to form the NC domain and confer the toxin insect-specific bioactivity. Conformational heterogeneity is observed in the solution of BmKalphaIT01 and could be attributed to the cis-trans isomerization of the peptide bond between residues 9 and 10. The minor conformation of BmKalphaIT01 with a trans peptide bond between Asn9 and Tyr10 may be responsible for its moderate bioactivity against mammals. The cis-trans isomerization of the peptide bond between residues 9 and 10 may be the structural basis of dual pharmacological activities of alpha-insect and alpha-like scorpion toxins, which is supported by the fact that conformational heterogeneity occurs in the solution structures of LqhalphaIT, LqqIII, and LqhIII and by comparison of the solution structure of BmKalphaIT01 with those of some relevant alpha-type toxins.
通过二维核磁共振光谱和分子建模技术，已确定了来自东亚钳蝎（Buthus martensii Karsch）的一种α-昆虫毒素BmKalphaIT01的溶液结构。结合序列同源性比较和毒性生物测定，BmKalphaIT01被认为是α-昆虫毒素的天然突变体，因此可作为研究这类毒素结构与功能关系的工具。BmKalphaIT01的整体结构具有一个共同的核心结构，由一个α-螺旋与一个三股反平行β-折叠堆积而成，在连接这些二级结构元件的环内呈现出独特的局部构象。BmKalphaIT01的溶液结构特征是Asn9和Tyr10之间存在一个非脯氨酸顺式肽键，该键被认为介导了五残基转角（Gln8-Cys12）和C端片段（Arg58-His64）的空间闭合，形成NC结构域并赋予毒素昆虫特异性生物活性。在BmKalphaIT01的溶液中观察到构象异质性，这可能归因于残基9和10之间肽键的顺反异构化。Asn9和Tyr10之间具有反式肽键的BmKalphaIT01的次要构象可能是其对哺乳动物具有中等生物活性的原因。残基9和10之间肽键的顺反异构化可能是α-昆虫毒素和α-样蝎毒素双重药理活性的结构基础，LqhalphaIT、LqqIII和LqhIII的溶液结构中存在构象异质性以及将BmKalphaIT01的溶液结构与一些相关α型毒素的结构进行比较均支持了这一观点。
