Functional mapping of the A2 domain from human factor VIII

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Coagulation factor VIII (FVIII) is a vital glycoprotein for blood clotting.
• The FVIII A2 domain is a critical structural component influencing its cofactor function.

Purpose of the Study:

• To identify specific residues within the FVIII A2 domain crucial for maintaining its cofactor activity.
• To map the structural and functional importance of amino acids in the FVIII A2 domain.

Main Methods:

• Generated 206 alanine substitution mutants within the FVIII A2 domain.
• Expressed mutants in COS-1 cells and measured antigen levels and procoagulant activities.
• Classified mutants based on activity loss and analyzed mutation sensitivity patterns.

Main Results:

• Identified 63 mutants with severely affected activity (<15%) and 98 with non-detrimental alterations (>50%).
• Found clusters of mutation-sensitive residues (e.g., Arg418-Phe436) buried within the A2 domain, suggesting structural roles.
• Identified mutation-resistant residues forming external loops, less critical for factor X activation.

Conclusions:

• Detailed map of FVIII A2 domain (residues 371-649) created, highlighting functionally critical residues.
• Buried residues are essential for A2 domain structure and FVIII function, while external loops are less critical.
• Identified residues crucial for FVIII function and those amenable to mutation without compromising coagulant activity.