A novel soluble tissue factor variant with an altered factor VIIa binding interface

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Engineering

Background:

• Tissue factor (TF) and factor VIIa (FVIIa) interaction is crucial for blood coagulation.
• Specific residues Lys20 and Asp58 in TF are critical for high-affinity FVIIa binding.
• Developing TF-based antagonists requires understanding and modifying these binding interactions.

Purpose of the Study:

• To engineer novel tissue factor (TF) variants with enhanced affinity for factor VIIa (FVIIa).
• To investigate the impact of specific residue modifications at the TF-FVIIa binding interface.
• To elucidate the binding mechanism of engineered TF variants.

Main Methods:

• Construction and display of TF variant libraries on bacteriophage M13.
• Phage display selection and sorting based on FVIIa binding affinity.
• Biochemical characterization of soluble TF (sTF) variants, including binding assays and cofactor activity measurements.

Main Results:

• Initial library screening yielded predominantly wild-type TF sequences.
• A targeted strategy fixing Lys20 to alanine and randomizing nearby residues identified a consensus variant with Tryptophan at position 58 (K20A,D58W).
• The K20A,D58W TF variant exhibited FVIIa binding affinity comparable to wild-type sTF but was cofactor-defective for factor X activation.

Conclusions:

• Modifying the TF-FVIIa binding interface can yield variants with altered functional properties.
• The K20A,D58W variant's binding mechanism appears distinct from wild-type TF, involving more than simple hydrophobic interactions.
• Further research is needed to fully understand the structural and mechanistic basis of the enhanced binding and defective cofactor activity.