Insights from structure-function studies of variant fibrinogen

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  • March 20, 2019
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  • Bowley, Sheryl Rubio
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Studies have linked fibrinogen and fibrin clot structure, strength and stability to cardiovascular diseases. Fibrinogen is a central participant in hemostasis, the maintenance of the delicate balance between clot formation and dissolution. During coagulation, thrombin converts soluble fibrinogen into insoluble fibrin polymer. Thrombin first cleaves fibrinopeptides A, exposing knobs "A" that spontaneously bind to holes "a" in another fibrin molecules forming "A:a" interactions. These interactions lead to the assembly of two parallel strands of fibrin molecules called protofibrils that are connected end-to-end by D:D interactions. Polymerization progresses with the lateral aggregation of protofibrils, during which, thrombin cleaves fibrinopeptide B exposing knobs "B" that bind to a complementary site called hole "b" in another molecule. This lateral aggregation of protofibrils form thicker fibers that grow, branch and form a network. Although the development of the method for engineering variant fibrinogens has provided enormous information regarding critical residues in fibrin polymerization, the full impact of the mutations on polymerization is not complete without structural data. In this work, the molecular bases for the impairment seen in fibrinogen variants were studied by functional assays and structural analysis. Fibrinogens that target mutations in hole "a" were studied to characterize "A:a" interactions. Biochemical and structural data showed that electrostatic interactions in hole "a" facilitate the important first step in fibrin polymerization. While the critical role of "A:a" interactions are well-established, the importance of "B:b" knob-hole interactions had been a matter of great debate. In this study, structural and biochemical analyses of variant recombinant fibrinogen that has a mutation in hole "b" showed "B:b" interactions have little influence on fibrin polymerization. It is likely that the loss of fibrinopeptide B rather than the gain of "B:b" interactions modulate lateral aggregation during fibrin polymerization. The impact of D:D interactions in fibrin polymerization was also explored in this study. Using variant fibrinogen with mutation at the D:D interface patterned after those found in patients, the molecular basis for the functional impairment of this abnormal fibrinogen was examined by combined biochemical and structural studies. Results showed that charge complementarities at the D:D interface during end-to-end association of fibrin molecules is important; that D:D interactions may be interdependent with other interactions in fibrin. These studies provided better understanding of the mechanism of fibrin formation which will likely enhance our ability to diagnose and design therapeutics for bleeding and thrombotic disorders.
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  • In Copyright
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  • Lord, Susan T.
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  • Open access
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  • October 11, 2010

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