The structure of a Michaelis serpin-protease complex.

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Serine protease inhibitors (serpins) regulate protease activity by forming covalent acyl-enzyme complexes.
• This inhibition involves massive conformational changes within the serpin structure.
• Understanding the initial interaction is key to elucidating the complete inhibition mechanism.

Purpose of the Study:

• To determine the structure of a serpin-trypsin Michaelis complex.
• To characterize the interaction surface between serpins and proteases.
• To provide a template for modeling other serpin-protease interactions.

Main Methods:

• Utilized an S195A trypsin mutant to prevent covalent complex formation, enabling visualization of the Michaelis complex.
• Structural analysis of the serpin-trypsin encounter complex.
• Investigated the impact of mutations at the serpin-protease interface on inhibitory activity.

Main Results:

• Revealed an extensive interaction surface in the serpin-trypsin encounter complex, larger than in small inhibitor-protease complexes.
• Identified specific serpin residues at the interface crucial for inhibitory activity.
• Observed a closer-than-usual interaction between a C-terminal serine residue and trypsin's active site His57.

Conclusions:

• The reported structure serves as a template for modeling other serpin-protease interactions.
• The extensive interface and specific residue interactions are critical for serpin-mediated protease inhibition.
• This provides a deeper understanding of the initial steps in serpin-protease complex formation and inhibition.