title: Structural/functional characterization of the alpha 2-plasmin inhibitor C-terminal peptide.
abstract: The alpha(2)-plasmin inhibitor (A2PI) is a main physiological regulator of the trypsin-like serine proteinase plasmin. It is composed of an N-terminal 15 amino acid fibrin cross-linking polypeptide, a 382-residue serpin domain, and a flexible C-terminal segment. The latter, peptide Asn(398)-Lys(452), and its Lys452Ala mutant were expressed as recombinant proteins in Escherichia coli (r-A2PIC and r-A2PICmut, respectively). CD and NMR analyses indicate that r-A2PIC is flexible, loosely folded, and with low content of regular secondary structure. Functional characterization via intrinsic fluorescence ligand titrations shows that r-A2PIC interacts with the isolated plasminogen kringle 1 (r-K1) (K(a) approximately 69.9 mM(-)(1)), K4 (K(a) approximately 45.7 mM(-)(1)), K5 (K(a) approximately 4.3 mM(-)(1)), and r-K2 (K(a) approximately 3.2 mM(-)(1)), all of which are known to exhibit lysine-binding capability. The affinities of these kringles for r-A2PIC are consistently larger than those reported for the ligand N(alpha)-acetyllysine, a mimic of a C-terminal Lys residue. The r-A2PICmut, with a C-terminal Ala residue, also interacts with r-K1 and K4, although with approximately 5-fold lesser affinities relative to r-A2PIC, demonstrating that while Lys(452) plays a major role in the binding, internal residues in r-A2PIC tether the kringles. (1)H NMR spectroscopy shows that key aromatic residues within the K4 lysine-binding site (LBS), namely, Trp(25), Trp(62), Phe(64), Trp(72), and Tyr(74), selectively respond to the addition of r-A2PIC and r-A2PICmut, indicating that these interactions proceed via the kringles' canonical LBS. We conclude that r-A2PIC docks to kringles primarily through lysine side chains and that Lys(452) most definitely enhances the binding. This suggests that multiple Lys residues within A2PI could contribute, perhaps in a zipper-like fashion, to its binding to the in-tandem, multikringle array that configures the plasmin heavy chain.
authors.affiliation: Department of Chemistry and Biochemistry, University of Berne, Freiestrasse 3, CH-3012 Berne, Switzerland.
authors.forename: Pascal S
authors.initials: PS
authors.lastname: Frank
authors.forename: Justin T
authors.initials: JT
authors.lastname: Douglas
authors.forename: Michael
authors.initials: M
authors.lastname: Locher
authors.forename: Miguel
authors.initials: M
authors.lastname: Llinás
authors.forename: Johann
authors.initials: J
authors.lastname: Schaller
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006801:Humans; D018082:Kringles / Q000235:genetics; D008239:Lysine / Q000737:chemistry / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010958:Plasminogen / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D000979:alpha-2-Antiplasmin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D010446:Peptide Fragments; D011994:Recombinant Proteins; D000979:alpha-2-Antiplasmin; D010958:Plasminogen; D008239:Lysine