Structural Investigations into the Serum Endonuclease Dnase1L3, as it Relates to Systemic Lupus Erythematous

Abstract

Systemic Lupus Erythematosus (SLE) afflicts at least 5 million people worldwide. SLE is an autoimmunological disease characterized by multisystem inflammation. SLE has poly and monogenic etiologies. SLE is characterized by anti-dsDNA antibodies and anti-neutrophil cytoplasmic antibodies. Dnase1L3 is primarily expressed by myeloid cells in the blood, and dendritic and macrophage cells in the liver and spleen as an excreted endonuclease. Dnase1L3 is a serum endonuclease in the Dnase1 family, that cleaves phosphodiester bonds in dsDNA. As contrasted with Dnase1, Dnase1L3 is more active in apoptotic microparticle degradation and, has more activity in chromatin DNA laddering. Undigested apoptotic microparticles and chromatin cause anti-dsDNA antibodies that give rise to lupus symptoms. Loss of function mutations (such as R206C and a murine mutation T89I) in Dnase1L3 are associated with pediatric onset lupus in humans. Dnase1L3 is not inhibited by actin and shows higher degradation activity than Dnase1 against DNA-protein complexes, this makes Dnase1L3 an important immunological enzyme, as well as a valuable biotechnical tool. The C-terminus helix present in Dnase1L3 homology models, likely explains some of the function of Dnase1l3. The C- terminal helix represents a substantial difference in secondary structure from Dnase1. Here we explore the relation of the C-terminal helix to vesicle interactions, through lipid vesicle co-sedimentation assays. While the structure for Dnase1 is known, the structure for Dnase1L3 is still unknown. Dnase1 has been proven ineffective as an enzyme therapy for SLE but, combined with Dnase1L3 effectiveness may increase. To investigate the potential for Dnase1L3 to be utilized in enzyme therapy research, we first need to understand the structural basis that underlies Dnase1L3's immunological disorder preventing activity. This is accomplished through expression, purification and, crystallization of Dnase1L3. Towards the end of structural analysis through X-ray crystallography.