title: Alpha-1-proteinase inhibitor is a heparin binding serpin: molecular interactions with the Lys rich cluster of helix-F domain.
abstract: Alpha-1-proteinase (alpha-1-PI) inhibitor is the major circulating serine protease inhibitor in humans. The porcine elastase and trypsin inhibitory activity of human and ovine alpha-1-PI is activated several fold in the presence of anti-coagulant heparin. The activation is allosteric and appears to be characterized by two steps of binding; a weak followed by a strong binding. The Kass for ovine and human alpha-1-PI inhibition of porcine pancreatic elastase was increased approximately 45 fold and 38 fold respectively. Using a combinatorial approach of multiple sequence alignment, surface topology, chemical modification and tryptic peptide mapping to identify the sequence of the heparin bound peptide; we demonstrate that heparin binds to the lysyl rich region of the F-helix of alpha-1-PI, which differs from that of heparin-antithrombin (AT) interactions. Molecular docking prediction using the MEDock algorithm approximates the three positively charged lysines (K154, K155, K174) of human alpha-1-PI in this interaction. This heparin alpha-1-PI interaction has been exploited to develop an affinity purification method, which can be used universally to obtain homogenous preparations of mammalian alpha-1-PIs useful for augmentation therapy. Collectively, all these findings imply that alpha-1-PI has a major role in regulating extra cellular protease activity and the physiological activator is heparin.
authors.affiliation: Department of Protein Chemistry and Technology, Central Food Technological Research Institute, Mysore 570020, India.
authors.forename: Vivek Kumar
authors.initials: VK
authors.lastname: Gupta
authors.forename: Lalitha R
authors.initials: LR
authors.lastname: Gowda
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000378:metabolism*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000737:chemistry* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000515:alpha 1-Antitrypsin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D015843:Serpins; D000515:alpha 1-Antitrypsin; D006493:Heparin; D008239:Lysine