Visualization of purified fibronectin-transglutaminase complexes

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Human erythrocyte transglutaminase forms a complex with plasma fibronectin near its collagen-binding domain.
• Transglutaminases are enzymes involved in protein cross-linking.

Purpose of the Study:

• To investigate if guinea pig liver transglutaminase also forms a complex with human fibronectin.
• To characterize the binding stoichiometry, location, and functional consequences of this interaction.

Main Methods:

• Nondenaturing electrophoresis
• Anisotropic fluorescence shifts
• Glycerol gradient zone sedimentation
• Rotary shadowing electron microscopy
• Sedimentation equilibrium

Main Results:

• Guinea pig liver transglutaminase forms a complex with human fibronectin, similar to the erythrocyte enzyme.
• Both enzymes bind fibronectin with a 2:1 stoichiometry.
• Transglutaminase binds to fibronectin within 5-10 nm of the N terminus, near the collagen-binding domain.
• Complex formation inhibits fibrinogen polymerization by erythrocyte transglutaminase.
• Electron microscopy revealed transglutaminase binding to the fibronectin strand, sometimes forming ring-like structures.

Conclusions:

• Transglutaminase binding to fibronectin is conserved across species and enzyme sources.
• The interaction occurs near the collagen-binding domain and affects enzyme function.
• The binding site and stoichiometry provide insights into the molecular mechanism of transglutaminase-fibronectin interaction.