# Expression and purification of human neutrophil proteinase 3 from insect cells and characterization of ligand binding

## TL;DR

This paper describes a method to produce and purify human neutrophil proteinase 3 (PR3) from insect cells for drug discovery in lung diseases.

## Contribution

The study introduces a reliable method for expressing and purifying active recombinant PR3 for drug discovery.

## Key findings

- Recombinant PR3 expressed in insect cells is highly pure and active.
- The activity of recombinant PR3 matches that of native human PR3 in enzymatic assays.
- A surface plasmon resonance-based assay was developed to study PR3 ligand binding.

## Abstract

Neutrophil proteinase 3 (PR3) is an important drug target for inflammatory lung diseases such as chronic obstructive pulmonary disease and cystic fibrosis. Drug discovery efforts targeting PR3 require active enzyme for in vitro characterization, such as inhibitor screening, enzymatic assays, and structural studies. Recombinant expression of active PR3 overcomes the need for enzyme supplies from human blood and in addition allows studies on the influence of mutations on enzyme activity and ligand binding. Here, we report the expression of recombinant PR3 (rPR3) using a baculovirus expression system. The purification and activation process described resulted in highly pure and active PR3. The activity of rPR3 in the presence of commercially available inhibitors was compared with human PR3 by using a fluorescence-based enzymatic assay. Purified rPR3 had comparable activity to the native human enzyme, thus being a suitable alternative for enzymatic studies in vitro. Further, we established a surface plasmon resonance-based assay to determine binding affinities and kinetics of PR3 ligands. These methods provide valuable tools for early drug discovery aiming towards treatment of lung inflammation.