2WBC: REFINED CRYSTAL STRUCTURE (2.3 ANGSTROM) OF A WINGED BEAN CHYMOTRYPSIN INHIBITOR AND LOCATION OF ITS SECOND REACTIVE SITE

Citation:
Abstract
The crystal structure of a double-headed alpha-chymotrypsin inhibitor, WCI, from winged bean seeds has now been refined at 2.3 A resolution to an R-factor of 18.7% for 9,897 reflections. The crystals belong to the hexagonal space group P6(1)22 with cell parameters a = b = 61.8 A and c = 212.8 A. The final model has a good stereochemistry and a root mean square deviation of 0.011 A and 1.14 degrees from ideality for bond length and bond angles, respectively. A total of 109 ordered solvent molecules were localized in the structure. This improved structure at 2.3 A led to an understanding of the mechanism of inhibition of the protein against alpha-chymotrypsin. An analysis of this higher resolution structure also helped us to predict the location of the second reactive site of the protein, about which no previous biochemical information was available. The inhibitor structure is spherical and has twelve anti-parallel beta-strands with connecting loops arranged in a characteristic beta-trefoil fold common to other homologous serine protease inhibitors in the Kunitz (STI) family as well as to some non homologous functionally unrelated proteins. A wide variation in the surface loop regions is seen in the latter ones.
PDB ID: 2WBCDownload
MMDB ID: 58254
PDB Deposition Date: 1997/11/26
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2.3  Å
Source Organism:
Similar Structures:
Biological Unit for 2WBC: monomeric; determined by author
Molecular Components in 2WBC
Label Count Molecule
Protein (1 molecule)
1
Chymotrypsin Inhibitor
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB
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