Exploring the Importance of Dimerization for DJ‐1 Function through Engineered Domain Fusions

Parkinson's Disease is a progressive neurodegenerative disease that affects approximately 6.3 million people worldwide and is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. DJ‐1 (PARK7) is one of several genes that are mutated in rare forms of familial parkinsonism. DJ‐1 is a dimeric cytoprotective protein that defends against oxidative stress and preserves mitochondrial function. Dimerization of DJ‐1 is thought to be essential for this function, as some disease‐associated mutations cause poor folding and disrupt the DJ‐1 dimer. However, recent reports suggest that DJ‐1 may be functional as a monomer. To test this, we have engineered a non‐dissociable DJ‐1 dimer that is a fusion of two human DJ‐1 domains. This construct cannot dissociate into monomers and thus will provide a stringent test of the importance of monomeric DJ‐1. Our engineered construct is modeled on plant DJ‐1 homologs, which feature naturally occurring duplicate DJ‐1 domains separated by a small (19 amino acid) linker region. Using X‐ray crystallography, we confirmed that this engineered non‐dissociable human DJ‐1 dimer has identical structure to the naturally occurring dimeric protein. We have investigated the influence of enforced dimerization of the pathogenic effects of the parkinsonian L166P and L10P mutations. CD spectroscopic analysis reveals that single and double L166P mutations in the non‐dissociable DJ‐1 dimer maintain a higher degree of structure than L166P mutations in the native protein. Additional characterization of the protective capacity and subcellular trafficking of this non‐dissociable DJ‐1 dimer in human cells is underway.