Mutations at over 60 positions within the 153-amino-acid enzyme known as Cu/Zn superoxide dismutase 1 (SOD1) have been linked to familial amyotrophic lateral sclerosis (fALS). The vast majority of these mutations are point substitutions. However, a small subset of mutations result in proteins that are C- terminally truncated. Studies in my laboratory, and the laboratories of my colleagues in this PPG, have provided evidence that the majority of disease associated point mutations in SOD1 leave the enzyme with significant normal activity;and most researchers in the field agree that disease is caused by a gained toxic property in the mutant enzymes. Over the past few years, we have been using mutagenesis to alter the properties of mutant SOD1, including mutations to eliminate the Cu-binding residues of the enzyme to test the role of Cu-mediated chemistry in a gained toxic property. These studies have demonstrated that versions of SOD1, encoding both disease-linked and experimental mutations to eliminate all four histidines that bind Cu, can cause motor neuron disease in transgenic mice. In the course of this work, we have documented that the brain stems and spinal cords of paralyzed transgenic mice accumulate high levels of aggregated and detergent insoluble forms of SOD1. We now propose to continue to use mutagenesis to accomplish two goals. In collaboration with Projects 1, 2, and Core A, we want to eliminate secondary sites in SOD1 that bind Cu and to study the role of Zn in stabilizing normal and abnormal structures (Aim 1). In collaboration with Project 2 and Core A, we want to define the role of SOD1 oligomerization in motor neuron disease (Aim 2). In addition, and in collaboration with Project 1 and Core A, we want to characterize the inclusion pathology that dominates the fALS mouse models. The real value in performing the proposed experiments proposed in Aims 1 and 2 within the context this Program Project grant is that we will now be able to study chemistry/structure/function relationships as we create and examine novel SOD1 variants. We will to document the metal status, chemistry, and structure of these novel mutants;and to then correlate these data to in vivo function in disease. Collectively, these investigations should allow us to map the elements within SOD1 that are required to elicit disease. Information that will greatly advance our understanding of how mutations in this protein may cause fALS.