4-羟基脯氨酸立体异构对α-芋螺毒素溶液构象的影响

在α-芋螺毒素及其它家族的芋螺毒素中, 脯氨酸的羟基化是非常普遍的后转录修饰方式. 在天然芋螺毒素中脯氨酸的羟基常采用反式构型, 且该残基对芋螺毒素的结构与生物活性产生了重要的影响, 而顺式构型的羟脯氨酸对α-芋螺毒素的折叠与生物活性的影响还鲜有研究. 本工作通过二维(2D)溶液核磁共振方法测定了经过化学修饰的三个含有反式或顺式羟脯氨酸的α-芋螺毒素的溶液结构, 它们是α4/7亚家族芋螺毒素肽γ15E]Sr1B、O7O'/γ15E]Sr1B和O6O'/γ14E]Vc1A. 研究表明, 羟基顺反异构化学修饰对芋螺毒素的结构影响显著. 羟脯氨酸羟基的反式到顺式修饰导致α-芋螺毒素肽明显的溶液构象变化, 这些变化包括二级结构的改变、关键残基的侧链取向变化以及氢键性质的改变. O7O'/γ15E]Sr1B与γ15E]Sr1B相比, 典型的α-芋螺毒素ω弯曲结构发生形变. 而O6O'/γ14E]Vc1A不同于Vc1A的是末端转角结构的缺失. 本工作加深了对α-芋螺毒素肽的化学修饰法的理解, 该方法是阐明α-芋螺毒素结构-生物活性关系的有用工具.

Effects of 4-Hydroxyproline Stereochemistry on α-Conotoxin Solution Conformation

The hydroxylation of proline is a post-translational modification common in α-conotoxin and other conotoxin families. The 4-hydroxyl group of hydroxyproline adopts a trans conformation in native conotoxin, and this residue plays a key role in toxin structure and bioactivity. Little is known about the effects of the cis conformation of 4-hydroxyproline on conotoxin folding and bioactivity. The solution structures of three chemically modified α-conotoxin species containing cis- and trans-4-hydroxyproline were investigated using two-dimensional nuclear magnetic resonance (2D NMR). The selected α4/ 7-conopeptides included γ15E]Sr1B, O7O'/γ15E]Sr1B, and O6O'/γ14E]Vc1A. The impact of modifying prolines cis/trans-4-hydroxyl group on the conopeptide structure was remarkable. Changing from trans- to cis-4-hydroxyproline led to notable solution conformational changes in α-conopeptide species. These included secondary structure elements, side chain orientations of key residues, and hydrogen-bonding properties. O7O'/γ15E]Sr1B exhibited a twisted ω structure unlike that of typical α-conotoxin species. O6O'/γ14E]Vc1A lost the turn structure around the N-/C-termini, which differed from that of Vc1.1. This study aids our understanding of the chemical modification of conotoxin, and is useful in elucidating the structure- bioactivity relationships of α-conotoxin species.