Squash Trypsin Inhibitors from Momordica cochinchinensis Exhibit an Atypical Macrocyclic Structure
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- 作者：Jean-Franç ; ois Hernandez ; Jean Gagnon ; Laurent Chiche ; Tuyet Mai Nguyen ; Jean-Pierre Andrieu ; Annie Heitz ; Thai Trinh Hong ; T. Trâ ; n Châ ; u Pham ; and Dung Le Nguyen
- 刊名：Biochemistry
- 出版年：2000
- 出版时间：May 16, 2000
- 年：2000
- 卷：39
- 期：19
- 页码：5722 - 5730
- 全文大小：292K
- 年卷期：v.39,no.19(May 16, 2000)
- ISSN：1520-4995
文摘
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-phaseHPLC. 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 insquash TIs. They contain 34 amino acid residues with 3 disulfide bridges and measured molecular massesof 3453.0 and 3480.7, respectively. They are the largest known macrocyclic peptides containing disulfidebridges. Their sequences show strong homology to other squash TIs, suggesting a similar three-dimensionalstructure and an analogous mechanism of action. A model of MCoTI-II was constructed by analogy tothe crystal structure of the complex between bovine trypsin and CMTI-I, indicating that the linker connectingthe two termini is flexible and does not impose significant geometrical constraints. This flexibility allowsan 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 resistanceto proteolysis. A minor species, MCoTI-III, was also characterized as containing 30 amino acid residueswith 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 inhibitionor by using their structure as natural scaffolds bearing new binding activities.