SOD1 dimerization monitoring using a novel split NanoLuc, NanoBit

In the present study, we applied a highly sensitive NanoLuc-based technology to understand the status of superoxide dismutase 1 (SOD1) within mammalian cells. Two fragments of NanoLuc (NanoBit), large N-terminal and small C-terminal regions, were fused with wild-type (wt) and mutant human SOD1 (hSOD1) genes and transfected into cells. Luciferase activity through NanoBit assembly was only detected in NanoBit-tagged wtSOD1-expressing cells. Furthermore, the developed NanoLuc system was used to investigate the role of protein-protein interactions in the pathogenesis of amyotrophic lateral sclerosis (ALS). In addition to SOD1, we also applied this NanoBit system for detecting the dimerization of wild-type, M337V-mutated human TAR-binding protein 43 kDa (hTDP43) and its cleaved C-terminal fragment (TDP25M337V ) as well as their interactions with SOD1. Luciferase activities of NanoBit-tagged mutant SOD1, TDP43, or TDP25 were negligible. Finally, we found that a zinc chelator partially reduced the luciferase activity of NanoBit-wtSOD1. Collectively, these results show that the present assay is sensitive and convenient to appreciate ALS and to develop useful agents for the modulation of SOD1 conformation.