Conformation and protease binding activity of binary and ternary human alpha 2-macroglobulin-protease complexes

Area of Science:

• Biochemistry
• Protease Inhibitors
• Protein Conformation

Background:

• Human alpha 2-macroglobulin (alpha 2M) is a large plasma proteinase inhibitor.
• alpha 2M undergoes significant conformational changes upon reaction with proteases.
• Understanding the stoichiometry and mechanism of protease binding to alpha 2M is crucial for its biological function.

Purpose of the Study:

• To investigate the conformational changes in alpha 2M induced by protease binding.
• To determine the binding stoichiometry and activity of alpha 2M-protease complexes.
• To evaluate the validity of the 'trap hypothesis' in describing alpha 2M-protease interactions.

Main Methods:

• Purification of alpha 2M-trypsin and alpha 2M-plasmin complexes using gel filtration chromatography.
• Binding assays using radioiodinated trypsin to assess protease binding activity of complexes.
• Analysis of protease binding stoichiometry and conformational changes.

Main Results:

• A single trypsin molecule binding to alpha 2M is sufficient to induce a conformational change.
• Binary alpha 2M-trypsin complexes exhibit no significant additional trypsin binding activity, despite available sites.
• Purified alpha 2M-plasmin complexes also showed no significant trypsin binding activity.

Conclusions:

• The reaction of alpha 2M with proteases follows the 'trap hypothesis'.
• Protease binding stoichiometry does not influence the conformational change or loss of binding activity.
• This mechanism is independent of protease size and applies broadly to alpha 2M interactions.