Properties of thrombin- and elastase-modified human antithrombin III

Area of Science:

• Biochemistry
• Protein Chemistry
• Structural Biology

Background:

• Human antithrombin III (AT) is a key inhibitor of coagulation proteases.
• Proteolytic modification can alter protein structure and function.
• Understanding structural changes in AT is crucial for anticoagulant therapy.

Purpose of the Study:

• To prepare and characterize proteolytically modified forms of human antithrombin III.
• To compare the structural and functional properties of modified AT with native AT.
• To investigate the stability and heparin-binding characteristics of modified AT.

Main Methods:

• Preparation of modified antithrombin III using thrombin, human neutrophil elastase, and porcine pancreatic elastase.
• Characterization using 1H NMR spectroscopy to analyze protein structure and histidine residue behavior.
• Assessment of protein stability through temperature-dependent unfolding studies and guanidine hydrochloride denaturation.
• Evaluation of heparin-binding domain behavior.

Main Results:

• Proteolytically modified AT forms exhibit identical NMR spectra and histidine titration parameters, differing significantly from native AT.
• Modified AT shows markedly increased thermal stability, remaining folded at temperatures far above native AT's unfolding point.
• The characteristic unfolding of the heparin-binding domain observed in native AT is absent in the modified forms.
• All three modified AT forms display identical behavior regarding temperature and stability.

Conclusions:

• Thrombin- and elastase-modified antithrombin possess identical structures, despite minor differences in cleavage sites.
• This modified structure is significantly different from that of native antithrombin III.
• The proteolytically modified forms of antithrombin demonstrate superior stability compared to the native protein.