SEMI-1, A Novel Neuronal Selenium-Binding Protein 1 Homolog Without Methanethiol Oxidase Activity, Modulates Stress...

Human selenium-binding protein 1 (SELENBP1) catalyzes the oxidation of the gaseous methionine degradation product, methanethiol. We previously identified a Caenorhabditis elegans ortholog, SEMO-1, that has the same methanethiol oxidase (MTO) activity. Here, we report the identification and functional characterization of another C. elegans ortholog of human SELENBP1, SEMI-1. In contrast to SELENBP1 and SEMO-1, SEMI-1 (SELENBP1-homolog, MTO inactive) lacks MTO activity. Notably, semi-1 expression is confined to thermosensory AFD (amphid finger-like endings D) and oxygen-sensing BAG (bag-like dendritic ending) neurons, as demonstrated using a SEMI-1::GFP reporter. Depletion of SEMI-1 results in increased lifespan, improved physiological parameters (motility, progeny), and reduced accumulation of age pigments during aging. SEMI-1-deficient nematodes are more resistant to the redox cycler paraquat than wild-type worms. On the other hand, they show enhanced susceptibility to selenite exposure, indicating a role for SEMI-1 in conferring selective stress resistance. We also show that SEMI-1 deficiency is associated with impaired thermotaxis in C. elegans, which is consistent with the role of AFD neurons in thermosensation. In conclusion, SEMI-1 is a neuronal SELENBP1 ortholog in C. elegans that lacks MTO activity and impairs oxidative stress resistance and shortens lifespan. As a trade-off, it contributes to C. elegans selenite resistance and thermotaxis. The observed phenotypes of SEMI-1 deficiency suggest the existence of MTO-independent effects of other SELENBP1 homologs.