Small Angle Neutron Scattering of Fibrinogen Polymerization Kinetics

Abstract

Fibrinogen is a plasma glycoprotein that is a major factor in the blood clotting process. In the presence of thrombin, fibrinogen polymerizes into a network of fibers called fibrin. Previous microscopy measurements show that the rate of polymerization affects the microscopic structure of the fibrin network. Although there is a good understanding of the blood clotting process, triggers and pathways, there are remaining questions regarding its kinetics and how the internal structure of fibrin develops. This study was designed to investigate how protein concentration and osmotic stress affect the rate of fibrinogen polymerization and the internal structure of the fibers. Dynamic light scattering measurements were done to quantify the relationship between the concentration ratio of fibrinogen to thrombin and the rate of polymerization. Time-resolved small-angle neutron scattering (SANS) experiments were performed to study the kinetics of fibrinogen polymerization, and contrast variation was used to study this process under osmotic stress. A suitable concentration ratio of fibrinogen (4 mg/ml) to thrombin (0.01 units/ml) was found to produce a polymerization reaction that lasts approximately 90 minutes; a reaction slow enough to yield a significant signal-to-noise ratio for SANS experiments. Various concentration series were measured using SANS. Guinier fits were used as a first approximation to obtain the radius of gyration (Rg) of the distinct domains of fibrinogen and fibrin. Pair distribution functions were used to monitor the shifts in structural parameters. SANS measurements show that osmotic stress affects fibrin structure and fibrinogen polymerization rate.