 |
PDBsum entry 1ib9
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Plant protein
|
PDB id
|
|
|
|
1ib9
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
Contents |
 |
|
|
|
|
|
|
|
|
* Residue conservation analysis
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Circular proteins in plants: solution structure of a novel macrocyclic trypsin inhibitor from momordica cochinchinensis.
|
|
|
Authors
|
|
M.E.Felizmenio-Quimio,
N.L.Daly,
D.J.Craik.
|
|
|
Ref.
|
|
J Biol Chem, 2001,
276,
22875-22882.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
