title: Dimeric crystal structure of a Bowman-Birk protease inhibitor from pea seeds.
abstract: The trypsin/chymotrypsin inhibitors from winter pea seeds (PsTI) are members of the Bowman-Birk protease inhibitor (BBPI) family. The crystal structure of the isoform PsTI-IVb was determined by molecular replacement at 2.7 A resolution using the X-ray co-ordinates of the soybean inhibitor as a search model. The inhibitor crystallized with a nearly perfect 2-fold symmetric dimer in the asymmetric unit. Although the overall structure is very similar to that seen in other BBPIs, there are notable new structural features. Unlike the previously reported X-ray structures of BBPIs, the structure of PsTI-IVb includes the C-terminal segment of the molecule. The C-terminal tail of each subunit is partly beta-stranded and interacts with the 2-fold symmetry-related subunit, forming a beta-sheet with strands A and B of this subunit. The dimer is mainly stabilized by a large internal hydrogen-bonded network surrounded by two hydrophobic links. Fluorescence anisotropy decay measurements show that residues Tyr59 and Tyr43 are mobile in the picosecond time scale with a large amplitude. The fluorescence study and a molecular model of the simultaneous binding of PsTI-IVb to porcine trypsin and bovine chymotrypsin are compatible only with a monomeric state of the functional molecule in solution.
authors.affiliation: Unité de Recherches de Biochimie et Structure des Protéines, INRA, Jouy-en-Josas Cedex, 78352, France.
authors.forename: I
authors.initials: I
authors.lastname: Li de la Sierra
authors.forename: L
authors.initials: L
authors.lastname: Quillien
authors.forename: P
authors.initials: P
authors.lastname: Flecker
authors.forename: J
authors.initials: J
authors.lastname: Gueguen
authors.forename: S
authors.initials: S
authors.lastname: Brunie
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002918:Chymotrypsin / Q000737:chemistry; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D019281:Dimerization; D005454:Fluorescence Polarization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000201:enzymology*; D010940:Plant Proteins / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D013552:Swine; D014357:Trypsin / Q000737:chemistry; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry*
chemical_list: D010940:Plant Proteins; D014358:Trypsin Inhibitor, Bowman-Birk Soybean; C050417:trypsin-chymotrypsin inhibitor A-II (peanut); D002918:Chymotrypsin; D014357:Trypsin