Evidence for essential lysines in heparin cofactor II

Area of Science:

• Biochemistry
• Protease Inhibitor Function
• Protein Modification

Background:

• Heparin cofactor II is a critical heparin-dependent plasma protease inhibitor.
• Lysyl residues play a role in the function of heparin cofactor II.
• Understanding these roles is key to comprehending protease inhibition mechanisms.

Purpose of the Study:

• To investigate the role of lysyl residues in heparin cofactor II function using covalent modification.
• To determine how modification affects heparin cofactor II's interaction with heparin and its inhibitory activities.

Main Methods:

• Covalent modification of heparin cofactor II using pyridoxal 5 omino-phosphate.
• Chemical reduction of Schiff base adducts with sodium borohydride.
• Assessing antithrombin and thrombin inhibition activities.
• Evaluating heparin binding capacity using heparin-agarose chromatography.

Main Results:

• Modification targeted 3-4 lysyl residues, with one protected by heparin.
• Antithrombin activity was enhanced in modified heparin cofactor II.
• Heparin cofactor activity for thrombin inhibition was significantly reduced or abolished.
• Modified heparin cofactor II lost its ability to bind to heparin-agarose.

Conclusions:

• Lysyl residues are essential for the heparin cofactor activity of heparin cofactor II in thrombin inhibition.
• Specific lysyl residues are involved in heparin binding and subsequent cofactor function.