Mapping of factor XIII solvent accessibility as a function of activation state using chemical modification methods

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Factor XIII (FXIII) is a transglutaminase crucial for blood coagulation.
• FXIII stabilizes fibrin clots by forming covalent cross-links.
• Activation of FXIII by thrombin and calcium ions is essential for its function.

Purpose of the Study:

• To investigate structural changes in FXIII during activation.
• To identify specific cysteine and lysine residues affected by activation.
• To understand how these modifications influence FXIII function.

Main Methods:

• Protein modification experiments using labeling of cysteine and lysine side chains.
• Comparison of labeling patterns between nonactivated and activated FXIII.
• Analysis of structural changes induced by physiological (thrombin) and nonproteolytic (calcium) activation.

Main Results:

• Significant differences in labeling patterns were observed between nonactivated and activated FXIII.
• Specific cysteine residues (Cys 314, Cys 409, Cys 695) and lysine residues (Lys 73, Lys 221) were identified as modified upon activation.
• Acetylation of Lys 73 and Lys 221, located in substrate recognition regions, occurs during activation.
• A lysine residue (Lys 677 or 678) in the beta-barrel 2 domain is acetylated in the zymogen but not in the activated enzyme.

Conclusions:

• FXIII activation leads to distinct structural alterations, including exposure or sequestration of specific residues.
• These modifications are critical for the enzyme's enhanced mechanical stability and resistance to degradation.
• The findings provide a comprehensive view of FXIII activation mechanisms and their functional consequences.