Solution structure of the squash trypsin inhibitor MCoTI-II. A new family for cyclic knottins
Solution structure of the squash trypsin inhibitor MCoTI-II. A new family for cyclic knottins
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DOI：
10.1021/bi0106639
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发表时间：
2001-07-10
期刊：
影响因子：
2.9
通讯作者：
Chiche, L
中科院分区：
文献类型：
--
作者：
Heitz, A;Hernandez, JF;Chiche, L
“结蛋白”折叠是一种稳定的富含半胱氨酸的支架，其中一个二硫键穿过由另外两个二硫键和连接主链片段形成的大环。这种支架存在于几个没有进化关系的蛋白质家族中。在过去的几年中，一些同源肽从茜草科和紫罗兰科的家庭被证明定义一个新的结构家族的基础上大环knottin折叠。我们最近从木麻黄种子中分离出第一个已知的大环南瓜胰蛋白酶抑制剂。这些化合物是一个新的环状knottins家族的第一批成员，在本文中，我们提出了其中之一，MCoTI-II，和P-Asp重排的形式，MCoTI-IIb的NMR结构研究。这两种化合物显示出相似且明确的构象。这些环状挤压抑制剂与非环状挤压抑制剂如CPTI-II具有相似的构象，并且推测环化的主要影响是对外部蛋白酶的敏感性降低。相反，检测到其他已知环状结蛋白的三维结构的明显差异，即，kalata B1或circulin A。两个二硫胱氨酸稳定的P-折叠基序[Heitz等人，（1999）Biochemistry 38，10615-10625]在两个家族中是保守的，而在C-至-N接头中，一个二硫键和一个环位于不同的位置。MCoTI-II的分子表面几乎完全带电，而环蛋白A则表现出明显的两亲性。这些差异可能解释了为什么从M. Cochinchinensis没有表现出明显的抗菌活性，而circulins和kalata B1则表现出明显的抗菌活性。
The "knottin" fold is a stable cysteine-rich scaffold, in which one disulfide crosses the macrocycle made by two other disulfides and the connecting backbone segments. This scaffold is found in several protein families with no evolutionary relationships. In the past few years, several homologous peptides from the Rubiaceae and Violaceae families were shown to define a new structural family based on macrocyclic knottin fold. We recently isolated from Momordica Cochinchinensis seeds the first known macrocyclic squash trypsin inhibitors. These compounds are the first members of a new family of cyclic knottins, In this paper, we present NMR structural studies of one of them, MCoTI-II, and of a P-Asp rearranged form, MCoTI-IIb. Both compounds display similar and well-defined conformations. These cyclic squash inhibitors share a similar conformation with noncyclic squash inhibitors such as CPTI-II, and it is postulated that the main effect of the cyclization is a reduced sensitivity to exo-proteases. On the contrary, clear differences were detected with the three-dimensional structures of other known cyclic knottins, i.e., kalata B1 or circulin A. The two-disulfide cystine-stabilized P-sheet motif [Heitz et al, (1999) Biochemistry 38, 10615-10625] is conserved in the two families, whereas in the C-to-N linker, one disulfide bridge and one loop are differently located. The molecular surface of MCoTI-II is almost entirely charged in contrast to circulin A that displays a well-marked amphiphilic character. These differences might explain why the isolated macrocyclic squash inhibitors from M. cochinchinensis display no significant antibacterial activity, whereas circulins and kalata B1 do.