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| [[Image:1ha9.gif|left|200px]] | | {{Seed}} |
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| {{STRUCTURE_1ha9| PDB=1ha9 | SCENE= }} | | {{STRUCTURE_1ha9| PDB=1ha9 | SCENE= }} |
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| '''SOLUTION STRUCTURE OF THE SQUASH TRYPSIN INHIBITOR MCOTI-II, NMR, 30 STRUCTURES.'''
| | ===SOLUTION STRUCTURE OF THE SQUASH TRYPSIN INHIBITOR MCOTI-II, NMR, 30 STRUCTURES.=== |
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| ==Overview==
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| 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 beta-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 beta-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. | | The line below this paragraph, {{ABSTRACT_PUBMED_11434766}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 11434766 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_11434766}} |
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| ==About this Structure== | | ==About this Structure== |
| 1HA9 is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Momordica_cochinchinensis Momordica cochinchinensis]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1HA9 OCA]. | | 1HA9 is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Momordica_cochinchinensis Momordica cochinchinensis]. Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1HA9 OCA]. |
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| ==Reference== | | ==Reference== |
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| [[Category: Plant protein]] | | [[Category: Plant protein]] |
| [[Category: Triple- stranded anti-parallel beta-sheet]] | | [[Category: Triple- stranded anti-parallel beta-sheet]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 18:37:54 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 1 07:53:29 2008'' |