Previous studies supported by NIH grant HL46213 (""""""""Molecular Interactions of Factor XI""""""""), for which continued support is sought, have focused attention on FXI and its interactions with other plasma proteins, i.e., thrombin, FXIa, FXIIa, prothrombin, high molecular weight kininogen (HK), and FIX, with the platelet plasma membrane and with various inhibitory molecules, e.g., protease nexin II (PN2), in the initiation and regulation of blood coagulation. These studies, utilizing NMR and x-ray crystallography, provide three separate structures, one of the catalytic domain of FXIa in complex with the KPI domain of PN2, one of the Apple 4 (A4) domain dimer and one of the zymogen FXI dimer that provide the basis for the future proposed investigations. The long-term goals of the present proposal are to elucidate the molecular mechanisms involved in the interaction of FXI/FXIa with protein and cell surface ligands involved in its activation and with plasma protein and cell surface ligands involved in the expression and regulation of FXIa enzymatic activity. Specifically these studies propose to determine the mechanism and physiological importance of FXI homodimer formation by a mutational analysis of the A4 dimer interface to prepare a monomeric FXI molecule;to study the role of the A4 domain in FXI dimerization in equilibrium unfolding studies;and to determine whether the dimeric structure of FXI is required for FXI activation to FXIa by thrombin or by FXIIa in the presence or absence of activated platelets or glycocalicin. They will examine the hypothesis that the activation of FXI to FXIa is accompanied by a major conformational change that promotes the efficient activation of FIX by exposing a substrate-binding site in the heavy chain (A2 and/or A3 domains) of FXIa for efficient binding and activation of FIX. Finally they will determine whether the dimeric structure of FXIa is required for efficient FIX-activation and to differentiate between alternative mechanisms to account for the failure of monomeric FXIa to activate FIX on the activated platelet surface. Recent observations resulting in the recognition of the essential role of FXI in hemostasis and thrombosis concern the relationship of its domain structure to its biological function, its molecular and cellular interactions, the elucidation of pathways for activation of FXI, and the expression and regulation of its enzymatic activity. It is hoped that information gleaned from the proposed studies will result in novel approaches to targeting FXI/XIa in the development of new anticoagulants that prevent thrombosis (heart attacks, strokes and pulmonary emboli) without bleeding complications.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Hemostasis and Thrombosis Study Section (HT)
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Link, Rebecca P
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Temple University
Internal Medicine/Medicine
Schools of Medicine
United States
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Navaneetham, Duraiswamy; Wu, Wenman; Li, Hongbo et al. (2013) P1 and P2' site mutations convert protease nexin-2 from a factor XIa inhibitor to a plasmin inhibitor. J Biochem 153:221-31
Marcinkiewicz, Mariola M; Sinha, Dipali; Walsh, Peter N (2012) Productive recognition of factor IX by factor XIa exosites requires disulfide linkage between heavy and light chains of factor XIa. J Biol Chem 287:6187-95
Wu, Wenman; Li, Hongbo; Navaneetham, Duraiswamy et al. (2012) The kunitz protease inhibitor domain of protease nexin-2 inhibits factor XIa and murine carotid artery and middle cerebral artery thrombosis. Blood 120:671-7
Su, Ya-Chi; Miller, Tara N; Navaneetham, Duraiswamy et al. (2011) The role of factor XIa (FXIa) catalytic domain exosite residues in substrate catalysis and inhibition by the Kunitz protease inhibitor domain of protease nexin 2. J Biol Chem 286:31904-14
Navaneetham, Duraiswamy; Sinha, Dipali; Walsh, Peter N (2010) Mechanisms and specificity of factor XIa and trypsin inhibition by protease nexin 2 and basic pancreatic trypsin inhibitor. J Biochem 148:467-79
Salameh, Moh'd A; Soares, Alexei S; Navaneetham, Duraiswamy et al. (2010) Determinants of affinity and proteolytic stability in interactions of Kunitz family protease inhibitors with mesotrypsin. J Biol Chem 285:36884-96
Salameh, Moh'd A; Robinson, Jessica L; Navaneetham, Duraiswamy et al. (2010) The amyloid precursor protein/protease nexin 2 Kunitz inhibitor domain is a highly specific substrate of mesotrypsin. J Biol Chem 285:1939-49
Kravtsov, Dmitri V; Matafonov, Anton; Tucker, Erik I et al. (2009) Factor XI contributes to thrombin generation in the absence of factor XII. Blood 114:452-8
Wu, Wenman; Sinha, Dipali; Shikov, Sergei et al. (2008) Factor XI homodimer structure is essential for normal proteolytic activation by factor XIIa, thrombin, and factor XIa. J Biol Chem 283:18655-64
Miller, Tara N; Sinha, Dipali; Baird, T Regan et al. (2007) A catalytic domain exosite (Cys527-Cys542) in factor XIa mediates binding to a site on activated platelets. Biochemistry 46:14450-60

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