title: Identification of the disulfide bonds in the recombinant somatomedin B domain of human vitronectin.
abstract: The NH(2)-terminal somatomedin B (SMB) domain (residues 1-44) of human vitronectin contains eight Cys residues organized into four disulfide bonds and is required for the binding of type 1 plasminogen activator inhibitor (PAI-1). In the present study, we map the four disulfide bonds in recombinant SMB (rSMB) and evaluate their functional importance. Active rSMB was purified from transformed Escherichia coli by immunoaffinity chromatography using a monoclonal antibody that recognizes a conformational epitope in SMB (monoclonal antibody 153). Plasmon surface resonance (BIAcore) and competitive enzyme-linked immunosorbent assays demonstrate that the purified rSMB domain and intact urea-activated vitronectin have similar PAI-1 binding activities. The individual disulfide linkages present in active rSMB were investigated by CNBr cleavage, partial reduction and S-alkylation, mass spectrometry, and protein sequencing. Two pairs of disulfide bonds at the NH(2)-terminal portion of active rSMB were identified as Cys(5)-Cys(9) and Cys(19)-Cys(21). Selective reduction/S-alkylation of these two disulfide linkages caused the complete loss of PAI-1 binding activity. The other two pairs of disulfide bonds in the COOH-terminal portion of rSMB were identified as Cys(25)-Cys(31) and Cys(32)-Cys(39) by protease-generated peptide mapping of partially reduced and S-alkylated rSMB. These results suggest a linear uncrossed pattern for the disulfide bond topology of rSMB that is distinct from the crossed pattern present in most small disulfide bond-rich proteins.
authors.affiliation: Department of Cell Biology, Division of Vascular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Yu-ichi
authors.initials: Y
authors.lastname: Kamikubo
authors.forename: Yuushi
authors.initials: Y
authors.lastname: Okumura
authors.forename: David J
authors.initials: DJ
authors.lastname: Loskutoff
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D003545:Cysteine / Q000737:chemistry; D004220:Disulfides; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes; D005822:Genetic Vectors; D006801:Humans; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D013002:Somatomedins / Q000737:chemistry*; D013997:Time Factors; D014361:Trypsin Inhibitors / Q000494:pharmacology; D019096:Vitronectin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004220:Disulfides; D000939:Epitopes; D011994:Recombinant Proteins; D013002:Somatomedins; D014361:Trypsin Inhibitors; D019096:Vitronectin; C016756:somatomedin B; D003545:Cysteine