Structural characteristics of the serum endonuclease Dnase1L3

Abstract

Abstract Systemic Lupus Erythematosus (SLE) is a debilitating autoimmune disease with poly- and mono-genic etiologies. One cause of monogenic SLE is the disruption of Dnase1L3. Dnase1L3 is a serum endonuclease that degrades chromatin in apoptotic microparticles. Dnase1L3 could represent a novel therapy for some cases of SLE. However, the structure of Dnase1L3 is predicted by the 42% identical protein Dnase1. To better understand the structure-function of Dnase1L3, we set out to solve the crystal structure. To solve the crystal structure, we first generated a recombinant His6-Maltose Binding Protein-Dnase1L3 fusion protein. We developed a protocol for purifying Dnase1L3. We isolated Dnase1L3 from the cell lysate using Nickel-NTA beads in maltose buffer, removed purification tags on Dnase1L3 with Tobacco Etch Virus protease, and purified Dnase1L3 on a negatively charged ion exchange column. We then purified Dnase1L3 by size exclusion chromatography to 96.7% final purity. We verified purity at each step by Coomassie staining and, confirmed identity of the final product by Western blot. Recombinant Dnase1L3 robustly degraded plasmid DNA, with a specific activity of 1.83 x 104 U/mg. We found Dnase1L3 had a propensity for small mosaic crystals in a Tris and MgCl2 crystallization buffer. However, larger crystals were grown at 7 °C, compared to 22 °C. Overall, we have developed a new purification method for generating active Dnase1L3 useful for crystallography and other high-purity applications. These applications will further our understanding of Dnase1L3 structure and its function in SLE.