Hill J M, Alewood P F, Craik D J
Centre for Drug Design and Development The University of Queensland, Brisbane, Queensland, 4072, Australia.
Structure. 1997 Apr 15;5(4):571-83. doi: 10.1016/s0969-2126(97)00212-8.
The venoms of Conus snails contain small, disulfide-rich inhibitors of voltage-dependent sodium channels. Conotoxin GS is a 34-residue polypeptide isolated from Conus geographus that interacts with the extracellular entrance of skeletal muscle sodium channels to prevent sodium ion conduction. Although conotoxin GS binds competitively with mu conotoxin GIIIA to the sodium channel surface, the two toxin types have little sequence identity with one another, and conotoxin GS has a four-loop structural framework rather than the characteristic three-loop mu-conotoxin framework. The structural study of conotoxin GS will form the basis for establishing a structure-activity relationship and understanding its interaction with the pore region of sodium channels.
The three-dimensional structure of conotoxin GS was determined using two-dimensional NMR spectroscopy. The protein exhibits a compact fold incorporating a beta hairpin and several turns. An unusual feature of conotoxin GS is the exceptionally high proportion (100%) of cis-imide bond geometry for the three proline or hydroxyproline residues. The structure of conotoxin GS bears little resemblance to the three-loop mu conotoxins, consistent with the low sequence identity between the two toxin types and their different structural framework. However, the tertiary structure and cystine-knot motif formed by the three disulfide bonds is similar to that present in several other polypeptide ion channel inhibitors.
This is the first three-dimensional structure of a 'four-loop' sodium channel inhibitor, and it represents a valuable new structural probe for the pore region of voltage-dependent sodium channels. The distribution of amino acid sidechains in the structure creates several polar and charged patches, and comparison with the mu conotoxins provides a basis for determining the binding surface of the conotoxin GS polypeptide.
芋螺毒液含有对电压依赖性钠通道具有抑制作用的、富含二硫键的小分子物质。芋螺毒素GS是一种从地纹芋螺中分离出的由34个氨基酸残基组成的多肽，它与骨骼肌钠通道的细胞外入口相互作用，以阻止钠离子传导。尽管芋螺毒素GS与μ-芋螺毒素GIIIA竞争性结合钠通道表面，但这两种毒素类型彼此间几乎没有序列同源性，并且芋螺毒素GS具有四环结构框架，而非典型的三环μ-芋螺毒素框架。对芋螺毒素GS的结构研究将为建立构效关系及理解其与钠通道孔区的相互作用奠定基础。
利用二维核磁共振光谱法测定了芋螺毒素GS的三维结构。该蛋白质呈现出一种紧密折叠结构，包含一个β发夹结构和几个转角。芋螺毒素GS的一个不同寻常的特征是，其三个脯氨酸或羟脯氨酸残基的顺式亚胺键几何结构比例异常高（100%）。芋螺毒素GS的结构与三环μ-芋螺毒素几乎没有相似之处，这与两种毒素类型之间低序列同源性及其不同的结构框架相一致。然而，由三个二硫键形成的三级结构和胱氨酸结基序与其他几种多肽离子通道抑制剂中的相似。
这是首个“四环”钠通道抑制剂的三维结构，它代表了一种用于电压依赖性钠通道孔区的有价值的新结构探针。结构中氨基酸侧链的分布产生了几个极性和带电荷的区域，与μ-芋螺毒素的比较为确定芋螺毒素GS多肽的结合表面提供了基础。
