Para-Benzoquinone (pBQ) Modifies Human Mitochondrial Phenylalanyl-tRNA Synthetase and Contributes to Mitochondrial Dysfunction.

Para-benzoquinone (pBQ) is of growing concern as an emerging redox-active environmental pollutant due to its ubiquitous presence in smoke and combustion byproducts. Recent reports have highlighted its potential role as a redox-driven mitotoxicant, although the involvement of specific mitochondrial protein targets remains unexplored. Here, we investigated the effects of pBQ on human mitochondrial phenylalanyl-tRNA synthetase (hmtPheRS), an essential enzyme required for mitochondrial protein synthesis and linked to severe neurodevelopmental disorders. Our biophysical analyses revealed that pBQ enhanced the formation of covalently modified higher-ordered structures of hmtPheRS by 75% and induced conformational instability, thereby significantly reducing its aminoacylation activity. NMR spectroscopy and molecular docking analyses further supported interactions between pBQ and residues within the catalytic domain of hmtPheRS, indicating the formation of a protein adduct. In parallel, exposure of HEK293 cells to sublethal concentrations of pBQ (20-40 μM) resulted in altered cellular redox homeostasis. It also impaired mitochondrial membrane potential and respiration, disrupted mitochondrial dynamics, and activated mitophagy. Consistent with the broad reactivity of pBQ and its ability to induce oxidative stress, these findings suggest that hmtPheRS is a vulnerable mitochondrial target whose modification may contribute to mitochondrial dysfunction, together with other redox-dependent pathways. Together, this work highlights mitochondrial aminoacyl-tRNA synthetases as an underexplored class of proteins susceptible to redox-active environmental pollutants.