A systematic immunoprecipitation approach reinforces the concept of common conformational alterations in amyotrophic lateral sclerosis-linked SOD1 mutants.

Mutations in the Cu, Zn superoxide dismutase (SOD1) gene are one of the causative agents of amyotrophic lateral sclerosis (ALS). Although more than 100 different mutations in SOD1 have been identified, it is unclear whether all the mutations are pathogenic or just single nucleotide polymorphisms (SNPs) unrelated to the disease. Our previous systematic analysis found that all pathogenic SOD1 mutants (SOD1(mut)) have a common property, namely, an association with Derlin-1, a component of the endoplasmic reticulum-associated degradation machinery. For the proposed mechanism, we found that most pathogenic SOD1(mut) have a constitutively exposed Derlin-1-binding region (DBR), which is concealed in wild-type SOD1 (SOD1(WT)). Moreover, we generated MS785, a monoclonal antibody against DBR. MS785 distinguished most ALS-causative SOD1(mut) from both SOD1(WT) and non-toxic SOD1(mut). However, MS785 could not recognize SOD1(mut) that has mutations in the MS785 epitope region. Here, we developed a new diagnostic antibody, which could compensate for this shortcoming of MS785. We hypothesized that in ALS-causative SOD1(mut), the DBR-neighboring region [SOD1(30-40)] may also be exposed. We then generated MS27, a monoclonal antibody against SOD1(30-40). We found that MS27 could distinguish SOD1(WT) from the pathogenic SOD1(mut), which has mutations in the MS785 epitope region. Moreover, all pathogenic SOD1(mut), without exception, were immunoprecipitated with a combination of MS785 and MS27. The MS785-MS27 combination could be developed as a novel mechanism-based biomarker for the diagnosis of ALS.