Bleeding through physical injury is stopped in animals through the formation of blood clots. Such clots, actually arising often in blood vessels without injury, can rupture due to the blood's shear forces and obstruct upstream smaller vessels leading to life threatening stroke, pulmonary embolism, and heart attack. Hence, a blood clot must be both mechanically stable to stop bleeding, yet elastic enough to avoid rupture. Fibrin, the main component of a blood clot, possesses the stated mechanical properties in healthy individuals, but in pathological circumstances needs to be managed through medication. Unfortunately, preventive treatment of blood clots is still a black art since the molecular basis of fibrin elasticity is unknown. Clinicians at the Mayo Clinic teamed up with computational biologists at the University of Illinois to investigate this elasticity, focusing on the protein fibrinogen, the building block of fibrin. The clinical researchers stretched individual fibrinogen molecules measuring the force needed to extend the molecules. They found a characteristic force - extension relationship and its dependence on blood pH and calcium concentration, but they could not interpret the finding chemically, a prerequisite for improving blood clot chemical management. The clinical researchers joined forces with computational biologists who could reproduce the measured force - extension relationship in steered molecular dynamics using NAMD. The simulations starting from known crystallographic structures of fibrinogen offered a full, i.e., atom resolution, chemical picture of fibrinogen elasticity. As reported recently by the clinical and computational researchers the insight gained opens new avenues for blood clot treatment. For example, it was found that pH and calcium concentrations alter the stiffness of blood clots, thereby opening pharmacological avenues for controlling the incidence of pathological blood clots. More on this investigation can be found here.

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