Solution Structure of the Squash Trypsin Inhibitor MCoTI-II. A New Family for Cyclic Knottins
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- 作者：Annie Heitz ; Jean-Franç ; ois Hernandez ; Jean Gagnon ; Thai Trinh Hong ; T. Trâ ; n Châ ; u Pham ; Tuyet Mai Nguyen ; Dung Le-Nguyen ; and Laurent Chiche
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：July 10, 2001
- 年：2001
- 卷：40
- 期：27
- 页码：7973 - 7983
- 全文大小：470K
- 年卷期：v.40,no.27(July 10, 2001)
- ISSN：1520-4995
文摘
The "knottin" fold is a stable cysteine-rich scaffold, in which one disulfide crosses themacrocycle made by two other disulfides and the connecting backbone segments. This scaffold is foundin several protein families with no evolutionary relationships. In the past few years, several homologouspeptides from the Rubiaceae and Violaceae families were shown to define a new structural family basedon macrocyclic knottin fold. We recently isolated from Momordica Cochinchinensis seeds the first knownmacrocyclic squash trypsin inhibitors. These compounds are the first members of a new family of cyclicknottins. In this paper, we present NMR structural studies of one of them, MCoTI-II, and of a 
le">-Asprearranged form, MCoTI-IIb. Both compounds display similar and well-defined conformations. Thesecyclic 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 thecontrary, clear differences were detected with the three-dimensional structures of other known cyclicknottins, i.e., kalata B1 or circulin A. The two-disulfide cystine-stabilized le">-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 almostentirely charged in contrast to circulin A that displays a well-marked amphiphilic character. Thesedifferences might explain why the isolated macrocyclic squash inhibitors from M. cochinchinensis displayno significant antibacterial activity, whereas circulins and kalata B1 do.
le">-Asprearranged form, MCoTI-IIb. Both compounds display similar and well-defined conformations. Thesecyclic 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 thecontrary, clear differences were detected with the three-dimensional structures of other known cyclicknottins, i.e., kalata B1 or circulin A. The two-disulfide cystine-stabilized le">-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 almostentirely charged in contrast to circulin A that displays a well-marked amphiphilic character. Thesedifferences might explain why the isolated macrocyclic squash inhibitors from M. cochinchinensis displayno significant antibacterial activity, whereas circulins and kalata B1 do.