title: Monoclonal antibody light chain with prothrombinase activity.
abstract: Prothrombin is the precursor of thrombin, a central enzyme in coagulation. Autoantibodies to prothrombin are associated with thromboembolism, but the mechanisms by which the antibodies modulate the coagulation processes are not understood. We screened a panel of 34 monoclonal antibody light chains isolated from patients with multiple myeloma for prothrombinase activity by an electrophoresis method. Two light chains with the activity were identified, and one of the light chains was characterized further. The prothrombinase activity eluted from a gel-filtration column run in denaturing solvent (6 M guanidine hydrochloride) at the characteristic positions of the light chain dimer and monomer. A constant level of catalytic activity was observed across the width of the light chain monomer peak, assessed as the cleavage of IEGR-methylcoumarinamide, a peptide substrate corresponding to residues 268-271 of prothrombin. Hydrolysis of this peptide by the light chain was saturable and consistent with Michaelis-Menten-Henri kinetics (K(m) 103 microM; k(cat) of 2.62 x 10(-)(2)/min). Four cleavage sites in prothrombin were identified by N-terminal sequencing of the fragments: Arg(155)-Ser(156), Arg(271)-Thr(272), Arg(284)-Thr(285), and Arg(393)-Ser(394). The light chain did not cleave radiolabeled albumin, thyroglobulin, and annexin V under conditions that readily permitted detectable prothrombin cleavage. Two prothrombin fragments (M(r) 55 000 and 38 000), were isolated by anion-exchange chromatography and were observed to cleave a thrombin substrate, tosyl-GPR-nitroanilide. Conversion of fibrinogen to fibrin was accelerated by the prothrombin fragments generated by the light chain. These finding suggest a novel mechanism whereby antibodies can induce a procoagulant state, i.e., prothrombin activation via cleavage of the molecule.
authors.affiliation: Departments of Internal Medicine and Pathology and Laboratory Medicine, Center for Chemical Immunology, University of Texas-Houston Medical School, 77030, USA. Perumal.Thiagarajan@uth.tmc.edu
authors.forename: P
authors.initials: P
authors.lastname: Thiagarajan
authors.forename: R
authors.initials: R
authors.lastname: Dannenbring
authors.forename: K
authors.initials: K
authors.lastname: Matsuura
authors.forename: A
authors.initials: A
authors.lastname: Tramontano
authors.forename: G
authors.initials: G
authors.lastname: Gololobov
authors.forename: S
authors.initials: S
authors.lastname: Paul
mesh_terms: D000911:Antibodies, Monoclonal / Q000302:isolation & purification / Q000378:metabolism* / Q000652:urine; D001777:Blood Coagulation; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000302:isolation & purification / Q000378:metabolism* / Q000652:urine; D007700:Kinetics; D009101:Multiple Myeloma / Q000276:immunology* / Q000652:urine; D010446:Peptide Fragments / Q000032:analysis; D011516:Prothrombin / Q000378:metabolism*; D013925:Thromboplastin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D007147:Immunoglobulin Light Chains; D010446:Peptide Fragments; D011516:Prothrombin; D013925:Thromboplastin