title: Conformational studies by 1H nuclear magnetic resonance of the trypsin-chymotrypsin inhibitor B-III from peanuts and its enzymatically modified derivative.
abstract: The conformation of the peanut inhibitor B-III was investigated by 1H NMR at 500 MHz. Resonances for about 30% of the residues were assigned and/or identified by conventional and two-dimensional 1H NMR measurements. The conformation of the modified inhibitor B-IIIRS, obtained by the cleavage of the peptide bonds of B-III at the first reactive site, Arg(10)-Arg(11), and second reactive site, Arg-(37)-Ser(38), was also investigated. Edman degradation was used to identify resonances of the residues adjoining the scissile sites. A comparison of the behavior of the resonances corresponding to Ala(12), Tyr(15), Phe(16), and Thr(37) in B-III and B-IIIRS indicated that the only conformational differences between the two proteins were those from the S-S loops containing the two reactive sites. From the similar behavior of Leu(7), Phe(24), His(26), Ala(29), five valine, and four threonine resonances in both proteins, it is suggested that the S-S loops that do not contain a scissile bond (the core region of the inhibitor) were rigid. Thus, no conformational change of the core region was observed upon cleavage of the reactive sites.
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010447:Peptide Hydrolases; D010940:Plant Proteins; D011487:Protein Conformation; D013816:Thermodynamics; D014357:Trypsin / Q000378:metabolism; D014361:Trypsin Inhibitors
chemical_list: D010940:Plant Proteins; D014361:Trypsin Inhibitors; C037954:trypsin-chymotrypsin inhibitor B-III, peanut; D010447:Peptide Hydrolases; D002918:Chymotrypsin; D014357:Trypsin