Proteome-Wide 4-Hydroxy-2-Nonenal Signature of Oxidative Stress in the Marine Invasive Tunicate Botryllus schlosseri

The ascidian Boytryllus schlosseri is a marine chordate that thrives under conditions of anthropogenic climate change. The B. schlosseri expressed proteome contains unusually high levels of proteins adducted with 4-hydroxy-2-nonenal (HNE). HNE represents a prominent posttranslational modification resulting from oxidative stress. Prior to this study, which identified 1052 HNE adducted proteins in B. schlosseri by LCMS, HNE protein modification has not been determined in any marine species. Adducted residues were ascertained for 1849 HNE modifications, 1195 of which had a maximum amino acid localization score. Most HNE modifications were at less reactive lysines (rather than more reactive cysteines). HNE prevalence on most sites was high, suggesting that B. schlosseri experiences and tolerates high intracellular reactive oxygen species levels, resulting in substantial lipid peroxidation. HNE adducted B. schlosseri proteins show enrichment in mitochondrial, proteostasis, and cytoskeletal functions. We propose that redox signaling contributes to regulating energy metabolism, the blastogenic cycle, oxidative burst defenses, and cytoskeleton dynamics in B. schlosseri. DIA-LCMS quantification of 72 HNE-adducted sites across 60 proteins revealed significant population-specific differences. We conclude that the vast amount of HNE protein adduction in this circumpolar tunicate is indicative of high oxidative stress tolerance contributing to its range expansion into diverse environments. Summary: Oxidative stress results from environmental challenges that increase in frequency and severity during the Anthropocene. Oxygen radical attack causes lipid peroxidation, leading to HNE production. Proteome-wide HNE adduction is highly prevalent in Botryllus schlosseri, a widely distributed, highly invasive, and economically important biofouling ascidian, and the first marine species to be analyzed for proteome HNE modification. HNE adduction of specific proteins may physiologically sequester reactive oxygen species, which could enhance fitness and resilience during environmental change.