Structure of the fibrin protofibril

Area of Science:

• Biochemistry
• Structural Biology
• Hematology

Background:

• Fibrin polymerization is essential for hemostasis and thrombosis.
• The precise structure of fibrin protofibrils and their assembly remains incompletely understood.

Purpose of the Study:

• To elucidate the molecular architecture of the two-stranded fibrin protofibril.
• To identify the intermolecular contacts governing fibrin polymerization.

Main Methods:

• Electron microscopy of negatively stained specimens.
• Structural modeling based on symmetry considerations.
• Analysis of trimer complexes.

Main Results:

• A model of the protofibril with two strands of trinodular fibrin molecules organized by specific rotational axes.
• Identification of staggered lateral contacts between central and outer nodules of adjacent strands.
• Identification of longitudinal contacts between outer nodules within a strand.
• Characterization of trimer complexes supporting the proposed molecular interactions.
• Postulation of a second lateral contact for protofibril association into thicker fibers.

Conclusions:

• The fibrin protofibril is a two-stranded structure held together by specific lateral and longitudinal molecular contacts.
• Three distinct intermolecular contacts are identified as critical for fibrin polymerization.
• This structural understanding provides insights into the mechanism of blood clot formation.