title: Unusual structural characteristics and complete amino acid sequence of a protease inhibitor from Phaseolus acutifolius seeds.
abstract: Two isoforms of a protease inhibitor were isolated by ion-exchange chromatography of tepary bean (Phaseolus acutifolius G.) seed proteins. The main isoform was used to determine the amino acid sequence of the protein. It is an 80 amino acid residue protein with a molecular mass of 8765 Da, showing sequence homology with the Bowman-Birk family of protease inhibitors. Several regions with amino acid microheterogeneity were found, corroborating the possible presence of isoforms. Mass spectrometry analysis was carried out to confirm isoforms. The presence of dimer and trimer forms of the inhibitor was shown through electrophoresis and mass spectrometry. Another unusual characteristic for this inhibitor was its ability to bind metals. The presence of four sequential histidines at the N-terminal end of the protein could account for this binding. Mass spectrometry and atomic absorption spectroscopy support the presence of calcium in the native inhibitor.
authors.affiliation: Unidad de Biotecnología y Prototipos, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México, Ap. Postal 314, 54000 Tlalnepantla, Edo. de México, Mexico.
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Campos
authors.forename: John R
authors.initials: JR
authors.lastname: Whitaker
authors.forename: Tai-Tung
authors.initials: TT
authors.lastname: Yip
authors.forename: T William
authors.initials: TW
authors.lastname: Hutchens
authors.forename: Alejandro
authors.initials: A
authors.lastname: Blanco-Labra
mesh_terms: D000595:Amino Acid Sequence; D002852:Chromatography, Ion Exchange; D008969:Molecular Sequence Data; D027805:Phaseolus / Q000737:chemistry*; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification; D011480:Protease Inhibitors / Q000737:chemistry*; D020033:Protein Isoforms; D012639:Seeds / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry
chemical_list: D010940:Plant Proteins; D011480:Protease Inhibitors; D020033:Protein Isoforms; D014358:Trypsin Inhibitor, Bowman-Birk Soybean