title: Cryocrystallography of a Kunitz-type serine protease inhibitor: the 90 K structure of winged bean chymotrypsin inhibitor (WCI) at 2.13 A resolution.
abstract: The crystal structure of a Kunitz-type double-headed alpha--chymotrypsin inhibitor from winged bean seeds has been refined at 2.13 A resolution using data collected from cryo-cooled (90 K) crystals which belong to the hexagonal space group P6(1)22 with unit-cell parameters a = b = 60.84, c = 207.91 A. The volume of the unit cell is reduced by 5.3% on cooling. The refinement converged to an R value of 20.0% (R(free) = 25.8%) for 11100 unique reflections and the model shows good stereochemistry, with r.m.s. deviations from ideal values for bond lengths and bond angles of 0.011 A and 1.4 degrees, respectively. The structural architecture of the protein consists of 12 antiparallel beta-strands joined in the form of a characteristic beta-trefoil fold, with the two reactive-site regions, Asn38-Leu43 and Gln63-Phe68, situated on two external loops. Although the overall protein fold is the same as that of the room-temperature model, some conformational changes are observed in the loop regions and in the side chains of a few surface residues. A total of 176 ordered water molecules and five sulfate ions are included in the model.
authors.affiliation: Crystallography Division, Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar, Calcutta 700 064, India.
authors.forename: S
authors.initials: S
authors.lastname: Ravichandran
authors.forename: U
authors.initials: U
authors.lastname: Sen
authors.forename: C
authors.initials: C
authors.lastname: Chakrabarti
authors.forename: J K
authors.initials: JK
authors.lastname: Dattagupta
mesh_terms: D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism; D018360:Crystallography, X-Ray; D007887:Fabaceae; D008958:Models, Molecular; D010940:Plant Proteins / Q000737:chemistry; D010946:Plants, Medicinal; D017510:Protein Folding; D017433:Protein Structure, Secondary; D015842:Serine Proteinase Inhibitors / Q000737:chemistry; D013431:Sulfates / Q000737:chemistry; D013696:Temperature; D014361:Trypsin Inhibitors / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D010940:Plant Proteins; D015842:Serine Proteinase Inhibitors; D013431:Sulfates; D014361:Trypsin Inhibitors; C440588:WCI protein, Psophocarpus tetragonolobus; D014867:Water; D002918:Chymotrypsin; C117608:alpha-chymotrypsin