title: A Novel Interaction between Complement Inhibitor C4b-binding Protein and Plasminogen That Enhances Plasminogen Activation.
abstract: The complement, coagulation, and fibrinolytic systems are crucial for the maintenance of tissue homeostasis. To date numerous interactions and cross-talks have been identified between these cascades. In line with this, here we propose a novel, hitherto unknown interaction between the complement inhibitor C4b-binding protein (C4BP) and plasminogen of the fibrinolytic pathway. Binding of C4BP to Streptococcus pneumoniae is a known virulence mechanism of this pathogen and it was increased in the presence of plasminogen. Interestingly, the acute phase variant of C4BP lacking the β-chain and protein S binds plasminogen much stronger than the main isoform containing the β-chain and protein S. Indeed, the complement control protein (CCP) 8 domain of C4BP, which would otherwise be sterically hindered by the β-chain, primarily mediates this interaction. Moreover, the lysine-binding sites in plasminogen kringle domains facilitate the C4BP-plasminogen interaction. Furthermore, C4BP readily forms complexes with plasminogen in fluid phase and such complexes are present in human serum and plasma. Importantly, whereas the presence of plasminogen did not affect the factor I cofactor activity of C4BP, the activation of plasminogen by urokinase-type plasminogen activator to active plasmin was significantly augmented in the presence of C4BP. Taken together, our data demonstrate a novel interaction between two proteins of the complement and fibrinolytic system. Most complexes might be formed during the acute phase of inflammation and have an effect on the homeostasis at the site of injury or acute inflammation.
authors.affiliation: From the Medical Protein Chemistry, Translational Medicine, Lund University, 20502 Malmö, Sweden.
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Agarwal
authors.affiliation: From the Medical Protein Chemistry, Translational Medicine, Lund University, 20502 Malmö, Sweden.
authors.forename: Simone
authors.initials: S
authors.lastname: Talens
authors.affiliation: From the Medical Protein Chemistry, Translational Medicine, Lund University, 20502 Malmö, Sweden.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Grandits
authors.affiliation: From the Medical Protein Chemistry, Translational Medicine, Lund University, 20502 Malmö, Sweden anna.blom@med.lu.se.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Blom
mesh_terms: D050716:Complement C4b-Binding Protein / Q000235:genetics / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D005341:Fibrinolysin / Q000378:metabolism; D005342:Fibrinolysis / Q000235:genetics; D006801:Humans; D007249:Inflammation / Q000378:metabolism* / Q000473:pathology; D008239:Lysine / Q000378:metabolism; D010958:Plasminogen / Q000235:genetics / Q000378:metabolism*; D010960:Plasminogen Activators / Q000378:metabolism; D011485:Protein Binding; D060066:Protein Interaction Maps; D017293:Protein S / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000378:metabolism* / Q000472:pathogenicity; D020349:Surface Plasmon Resonance; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
chemical_list: D050716:Complement C4b-Binding Protein; D017293:Protein S; D005340:Fibrinogen; D010958:Plasminogen; D010960:Plasminogen Activators; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator; D008239:Lysine
keywords: C4b-binding protein; complement; plasmin; plasminogen; protein-protein interaction; surface plasmon resonance (SPR)