Priebs, Josephine, Ridolfi, Verena Alexia, Philipp, Thilo Magnus, Kohnlein, Karl, Klotz, Lars-Oliver, Steinbrenner, Holger
[
International Worm Meeting,
2021]
The C. elegans ortholog of human selenium-binding protein 1 (SELENBP1), Y37A1B.5, is a pro-aging factor that confers resistance to high doses of selenite (1). SELENBP1 was recently identified as a methanethiol oxidase (MTO), catalyzing the conversion of methanethiol to hydrogen sulfide (H2S), hydrogen peroxide (H2O2) and formaldehyde. Here, we tested whether Y37A1B.5 has MTO activity and whether the AMPK orthologs AAK-1/-2 are involved in the effects of the protein on C. elegans lifespan. We developed an MTO activity assay that is based on in situ-generation of methanethiol from methionine as catalyzed by a bacterial recombinant L-methionine gamma-lyase, followed by detection of two methanethiol oxidation products, H2S and H2O2. Using this assay, we demonstrate MTO activity of isolated recombinant Y37A1B.5, similar to recombinant human SELENBP1. Moreover, MTO activity was detected in lysates from wild-type nematodes but not in lysates from a newly generated Y37A1B.5-deficient mutant strain, suggesting that the Y37A1B.5 protein is the major C. elegans MTO. Thus, Y37A1B.5 was named SEMO-1 (SELENBP1 ortholog with MTO activity). It is a novel methanethiol oxidase and therefore a novel potential source of H2S and H2O2, two molecules known to affect lifespan in C. elegans. A Y37A1B.5/SEMO-1-deficient mutant strain showed an extended lifespan similar to the previously reported worms exposed to Y37A1B.5-specific RNAi (1). SEMO-1, therefore, is a factor apparently shortening C. elegans lifespan. Interestingly, lifespan extension following SEMO-1 depletion was abrogated in an AAK-deficient strain (NB245; deficient in both isoforms of the catalytic AAK subunit), and vice versa, SEMO-1 depletion through RNAi appeared to enhance AAK phosphorylation in wild-type worms. As AAK activity is known to be related to C. elegans lifespan, we propose that the extended lifespan of SEMO-1-depleted worms is caused by AAK activation. The mode of AAK activation following SEMO-1 depletion remains to be identified. (1) Kohnlein K, Urban N, Guerrero-Gomez D, Steinbrenner H, Urbánek P, Priebs J, Koch P, Kaether C, Miranda-Vizuete A, Klotz LO. Redox Biol. 28:101323 (2020).
[
East Coast Worm Meeting,
2002]
Nematode surface proteins are thought to play a key role in the ability of nematodes' successful survival in diverse environments. It is possible that parasitic nematodes avoid attack by host immune responses by changing the proteins they display during infection (Politz and Philipp 1992; Blaxter et al 1992). Members of a specific class of mucin-like nematode surface proteins share a domain containing six cysteine residues arranged in a conserved spacing (referred to as the SXC domain, Gems and Maizels 1996, Blaxter 1998, Loukas et al 2000). Similar cysteine-rich sequences are found in many organisms; an important characteristic is the tendency of the cysteines to form disulfide bonds that help define the tertiary structure of the domains. To help understand evolutionary relationships between SXC domains of different species, an extensive set of SXC sequences was obtained by database searching, and similarities between amino acid sequences of the domains were determined. BLAST searching identified over 300 SXC domains in three nematode species and two sea anemone species. One of the sea anemone domains was previously known to correspond to a potassium channel-blocking toxins consisting of a single SXC domain (Dauplais et al 1997, Loukas et al 2000). Sequence alignments, evolutionary trees, and gene structure analysis demonstrated that the SXC sequences can be categorized as members of distinct families. The results suggest that the individual families of SXC domains were present before the duplication and divergence events that accompanied speciation and created the separate genes that contain the SXC sequences. Many genes encode more than one SXC domain, and sequence similarities suggest that many of the genes encoding six cysteine sequences from C. elegans and C. briggsae are orthologous. This tends to support the hypothesis that these species diverged after the formation of six cysteine families. Without more complete genome sequence information (e.g., from the sea anemone species that constitute an outgroup) it cannot be determined how ancient these family relationships are.