Crystal structure of wild-type human procathepsin K

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Cathepsin K, a cysteine protease in the papain superfamily, is a key mediator of osteoclastic bone resorption.
• Understanding the structure of procathepsin K is crucial for elucidating its regulatory mechanisms and potential therapeutic targeting.

Purpose of the Study:

• To determine the crystal structure of wild-type human procathepsin K.
• To analyze the binding mode of the proregion to cathepsin K and compare it with related proteases.

Main Methods:

• Crystallization of deglycosylated human procathepsin K.
• X-ray diffraction data collection to 3.2 Å resolution.
• Structure solution by molecular replacement and refinement.

Main Results:

• The crystal structure revealed a globular N-terminal proregion and an extended, flexible C-terminal segment.
• The proregion binds to the cathepsin K active site, interacting with the substrate binding groove and proregion binding loop.
• The binding mode shares similarities with other cysteine proteases but exhibits local differences, particularly in the alpha3p helix position, contributing to enzyme specificity.

Conclusions:

• The proregion of cathepsin K binds in an orientation opposite to natural substrates, suggesting a regulatory role.
• Structural comparisons highlight conserved and distinct features in proregion-enzyme interactions across the papain superfamily.
• The findings provide a structural basis for cathepsin K specificity and potential inhibitor design targeting bone resorption.