Peruvianin-I is a cysteine peptidase (EC 3.4.22) purified from Thevetia peruviana. Previous studies have shown that it is the only germin-like protein (GLP) with proteolytic activity described so far. In this work, the X-ray crystal structure of peruvianin-I was determined to a resolution of 2.15 Å (PDB accession number: 6ORM) and its specific location was evaluated by different assays. Its overall structure shows an arrangement composed of a homohexamer (a trimer of dimers) where each monomer exhibits a typical β-barrel fold and two glycosylation sites (Asn55 and Asn144). Analysis of its active site confirmed the absence of essential amino acids for typical oxalate oxidase activity of GLPs. Details of the active site and molecular docking results, using a specific cysteine peptidase inhibitor (iodoacetamide), were used to discuss a plausible mechanism for proteolytic activity of peruvianin-I. Histological analyses showed that T. peruviana has articulated anastomosing laticifers, i.e., rows of cells which merge to form continuous tubes throughout its green organs. Moreover, peruvianin-I was detected exclusively in the latex. Because latex peptidases have been described as defensive molecules against insects, we hypothesize that peruvianin-I contributes to protect T. peruviana plants against herbivory.

中文翻译：

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来自 Thevetia peruviana 的具有蛋白水解活性的类胚芽蛋白的晶体结构和特定位置

Peruvianin-I 是一种从 Thevetia peruviana 中纯化的半胱氨酸肽酶 (EC 3.4.22)。先前的研究表明，它是迄今为止描述的唯一具有蛋白水解活性的生芽样蛋白 (GLP)。在这项工作中，peruvianin-I 的 X 射线晶体结构被确定为分辨率为 2.15 Å（PDB 登录号：6ORM），并通过不同的测定评估其特定位置。其整体结构显示出由同六聚体（二聚体的三聚体）组成的排列，其中每个单体表现出典型的 β-桶状折叠和两个糖基化位点（Asn55 和 Asn144）。对其活性位点的分析证实了 GLP 的典型草酸氧化酶活性所必需的氨基酸的缺失。活性位点和分子对接结果的详细信息，使用特定的半胱氨酸肽酶抑制剂（碘乙酰胺），用于讨论 peruvianin-I 蛋白水解活性的合理机制。组织学分析表明，T. peruviana 具有铰接的吻合乳管，即成排的细胞合并形成贯穿其绿色器官的连续管。此外，仅在乳胶中检测到 peruvianin-I。因为乳胶肽酶被描述为针对昆虫的防御分子，我们假设 peruvianin-I 有助于保护 T. peruviana 植物免受食草动物的侵害。