PDBsum entry 1ib9

Plant protein

PDB id: 1ib9

Contents

Protein chain

34 a.a.

PDB id:

1ib9

Name:

Plant protein

Title:

Solution structure of mcoti-ii, a macrocyclic trypsin inhibitor

Structure:

Trypsin inhibitor ii. Chain: a. Synonym: mcoti-ii

Source:

Momordica cochinchinensis. Spiny bitter cucumber. Organism_taxid: 3674. Other_details: the protein is isolated from the seeds using sodium acetate.

NMR struc:

20 models

Authors:

M.E.Felizmenio-Quimio,N.L.Daly,D.J.Craik

Key ref:

M.E.Felizmenio-Quimio et al. (2001). Circular proteins in plants: solution structure of a novel macrocyclic trypsin inhibitor from Momordica cochinchinensis. J Biol Chem, 276, 22875-22882. PubMed id: 11292835 DOI: 10.1074/jbc.M101666200

Date:

28-Mar-01 Release date: 18-Jul-01

Protein chain

P82409  (ITR2_MOMCO) -  Trypsin inhibitor 2 from Momordica cochinchinensis

Seq: 34 a.a.

Struc: 34 a.a.

DOI no: 10.1074/jbc.M101666200

J Biol Chem 276:22875-22882 (2001)

PubMed id: 11292835

Circular proteins in plants: solution structure of a novel macrocyclic trypsin inhibitor from Momordica cochinchinensis.

M.E.Felizmenio-Quimio, N.L.Daly, D.J.Craik.

ABSTRACT

Much interest has been generated by recent reports on the discovery of circular (i.e. head-to-tail cyclized) proteins in plants. Here we report the three-dimensional structure of one of the newest such circular proteins, MCoTI-II, a novel trypsin inhibitor from Momordica cochinchinensis, a member of the Cucurbitaceae plant family. The structure consists of a small beta-sheet, several turns, and a cystine knot arrangement of the three disulfide bonds. Interestingly, the molecular topology is similar to that of the plant cyclotides (Craik, D. J., Daly, N. L., Bond, T., and Waine, C. (1999) J. Mol. Biol. 294, 1327-1336), which derive from the Rubiaceae and Violaceae plant families, have antimicrobial activities, and exemplify the cyclic cystine knot structural motif as part of their circular backbone. The sequence, biological activity, and plant family of MCoTI-II are all different from known cyclotides. However, given the structural similarity, cyclic backbone, and plant origin of MCoTI-II, we propose that MCoTI-II can be classified as a new member of the cyclotide class of proteins. The expansion of the cyclotides to include trypsin inhibitory activity and a new plant family highlights the importance and functional variability of circular proteins and the fact that they are more common than has previously been believed. Insights into the possible roles of backbone cyclization have been gained by a comparison of the structure of MCoTI-II with the homologous acyclic trypsin inhibitors CMTI-I and EETI-II from the Cucurbitaceae plant family.

Selected figure(s)

Figure 3.
Fig. 3. Comparison of the and aspartyl isomers of MCoTI-II. a, structure of and aspartic acid residues and sequential NOEs expected to be observed in the -Asp form. b, comparison of the -proton chemical shifts of the two isomers of MCoTI-II. The fact that the differences occur only near residue Asp-5 suggests that isomerization of this residue ( / aspartic acid) is responsible for the differences between the two isolated peptides.

Figure 8.
Fig. 8. The three-dimensional structure of MCoTI-II shown in CPK format. The negatively charged residues are in red, positively charged in dark blue, hydrophobic residues in green, polar residues in light blue, and cysteine residues in yellow. Surface exposed hydrophobic residues appear mainly on one face and the other face contains most of the positively and negatively charged residues. The views are rotated 180° about the vertical axis with respect to each other. The diagram was generated using MOLMOL (39).

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2001, 276, 22875-22882) copyright 2001.

Figures were selected by an automated process.