High molecular weight kininogen as substrate for cathepsin B

Area of Science:

• Biochemistry
• Enzymology
• Proteolysis

Background:

• High molecular weight kininogen (HMWK) is a precursor to bradykinin.
• Cathepsin B is a cysteine protease implicated in various physiological and pathological processes.
• The kininogenase activity of cathepsin B is not fully understood, particularly its regulation by environmental factors.

Purpose of the Study:

• To investigate the impact of pH and divalent cations (Zn2+, Mg2+, Ca2+) on the processing of HMWK by cathepsin B.
• To determine the optimal conditions for cathepsin B's kininogenase activity.
• To assess the relevance of HMWK processing by cathepsin B in pathophysiological contexts.

Main Methods:

• In vitro enzymatic assays using purified high molecular weight kininogen and cathepsin B.
• Incubation of substrates under varying pH conditions (6.3 and 7.35).
• Analysis of proteolytic fragments using SDS-PAGE and molecular weight determination.

Main Results:

• At pH 6.3, cathepsin B extensively hydrolyzed HMWK into 80, 60, and 40 kDa fragments.
• Cathepsin B exhibited enhanced kininogenase activity at pH 6.3 in the absence of divalent cations.
• At pH 7.35, HMWK showed minimal cleavage by cathepsin B, yielding a 60 kDa fragment, and its kininogenase activity was impaired.

Conclusions:

• Cathepsin B efficiently processes HMWK at acidic pH, indicating significant kininogenase activity.
• The presence of divalent cations inhibits cathepsin B's HMWK processing activity.
• These findings support the hypothesis that HMWK serves as a substrate for cathepsin B under pathophysiological conditions characterized by altered pH and cation concentrations.