title: Same fold with different mobility: backbone dynamics of small protease inhibitors from the desert locust, Schistocerca gregaria.
abstract: SGCI (Schistocerca gregaria chymotrypsin inhibitor) and SGTI (Sch. gregaria trypsin inhibitor) are small, 35-residue serine protease inhibitors with intriguing taxon specificity: SGTI is specific for arthropod proteases while SGCI is an excellent inhibitor on both mammalian and arthropodal enzymes. Here we report the cloning, expression, and (15)N backbone dynamics investigations of these peptides. Successful expression could be achieved by a "dimeric" construct similar to the natural precursor of the inhibitors. An engineered methionine residue between the two modules served as a unique cyanogen bromide cleavage site to cleave the precursor and physically separate SGCI and SGTI. The overall correlation time of the precursor (5.29 ns) as well as the resulted SGCI (3.14 ns) and SGTI (2.96 ns) are as expected for proteins of this size. General order parameters (S(2)) for the inhibitors are lower than those characteristic of well-folded proteins. Values in the binding loop region are even lower. Interestingly, the distribution of residues for which a chemical exchange (R(ex)) term should be considered is strikingly different in SGCI and SGTI. Together with H-D exchange studies, this indicates that the internal dynamics of the two closely related molecules differ. We suggest that the dynamic properties of these inhibitors is one of the factors that determine their specificity.
authors.affiliation: Department of Biochemistry, Eötvös Loránd University, 1117 Pázmány Street 1/C, Budapest, Hungary.
authors.forename: Borbála
authors.initials: B
authors.lastname: Szenthe
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Gáspári
authors.forename: Attila
authors.initials: A
authors.lastname: Nagy
authors.forename: András
authors.initials: A
authors.lastname: Perczel
authors.forename: László
authors.initials: L
authors.lastname: Gráf
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D006110:Grasshoppers / Q000737:chemistry* / Q000235:genetics; D019476:Insect Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D007700:Kinetics; D008969:Molecular Sequence Data; D036103:Nanotechnology / Q000379:methods; D009587:Nitrogen Isotopes / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D017510:Protein Folding; D011498:Protein Precursors / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D015842:Serine Proteinase Inhibitors / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D013816:Thermodynamics; D010455:Peptides
chemical_list: D019476:Insect Proteins; D009587:Nitrogen Isotopes; D011498:Protein Precursors; D015842:Serine Proteinase Inhibitors; C113210:LOC126284306 protein, Schistocerca gregaria; D010455:Peptides