Squash trypsin inhibitors from Momordica cochinchinensis exhibit an atypical macrocyclic structure
Squash trypsin inhibitors from Momordica cochinchinensis exhibit an atypical macrocyclic structure
复制标题
DOI：
10.1021/bi9929756
复制
发表时间：
2000-05-16
期刊：
影响因子：
2.9
通讯作者：
Nguyen, DL
中科院分区：
文献类型：
--
作者：
Hernandez, JF;Gagnon, J;Nguyen, DL
使用凝胶过滤、离子交换色谱和反相 HPLC 从南瓜 Momordica cochinchinensis (MCo) 种子中分离和纯化了三种胰蛋白酶抑制剂 (TI)。它们的序列只能在蛋白水解后才能确定。就 MCoTI-I 和 -II 而言，研究表明它们的多肽主链是环状的，这是南瓜 TI 中从未描述过的结构。它们含有 34 个氨基酸残基和 3 个二硫桥，测得的分子量分别为 3453.0 和 3480.7。它们是已知最大的含有二硫桥的大环肽。它们的序列与其他壁球 TI 表现出很强的同源性，表明具有相似的三维结构和类似的作用机制。通过类比牛胰蛋白酶和CMTI-I复合物的晶体结构构建了MCoTI-II模型，表明连接两个末端的连接子是灵活的并且不会施加显着的几何约束。这种灵活性允许在该区域发生天冬氨酸-甘氨酸肽键重排，产生两种 MCoTI-II 亚型。尽管环化的重要性尚不清楚，但它可能会提高稳定性和抗蛋白水解性。一个次要物种 MCoTI-III 也被表征为含有 30 个氨基酸残基，分子量为 3379.6。该组件具有带有封闭 N 末端的线性主链。 MCoTI 代表了药物设计的有趣候选者，可以通过改变其抑制特异性或通过使用其结构作为具有新结合活性的天然支架。
Three trypsin inhibitors (TIs), from the seeds of the squash Momordica cochinchinensis (MCo), have been isolated and purified using gel filtration, ion exchange chromatography, and reverse-phase HPLC. Their sequences could be determined only after proteolytic cleavages. In the case of MCoTI-I and -II, it was shown that their polypeptide backbones are cyclic, a structure that has never been described in squash TIs. They contain 34 amino acid residues with 3 disulfide bridges and measured molecular masses of 3453.0 and 3480.7, respectively. They are the largest known macrocyclic peptides containing disulfide bridges. Their sequences show strong homology to other squash TIs, suggesting a similar three-dimensional structure and an analogous mechanism of action. A model of MCoTI-II was constructed by analogy to the crystal structure of the complex between bovine trypsin and CMTI-I, indicating that the linker connecting the two termini is flexible and does not impose significant geometrical constraints. This flexibility allows an Asp-Gly peptide bond rearrangement to occur in this region, giving rise to two isoforms of MCoTI-II. Although the importance of cyclization is not clear, it might confer increased stability and resistance to proteolysis. A minor species, MCoTI-III, was also characterized as containing 30 amino acid residues with a molecular mass of 3379.6. This component possesses a linear backbone with a blocked N-terminus. MCoTIs represent interesting candidates for drug design, either by changing their specificity of inhibition or by using their structure as natural scaffolds bearing new binding activities.