{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nHuman RARS1 encodes the cytoplasmic arginyl-tRNA synthetase (ArgRS), a key enzyme that catalyzes the esterification of L‑arginine to its cognate tRNA—a critical step in protein translation. Structural and biochemical studies have revealed that ArgRS possesses an extended N‑terminal domain that is essential for its integration into the multi‑aminoacyl tRNA synthetase complex (MSC), where it forms critical contacts with auxiliary factors such as AIMP1. Crystallographic analyses further demonstrate that binding of L‑arginine or its analogs induces subtle conformational changes that optimize substrate recognition and catalytic efficiency. Moreover, alternative translational initiation generates two distinct ArgRS isoforms: one that is MSC‑associated and another that remains free in the cytosol, potentially diversifying its cellular functions. Recent work also indicates that binding of regulatory molecules like hemin to a conserved site in the Add1 domain can induce oligomerization and inhibit enzyme activity, suggesting additional layers of functional modulation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "5"}]}, {"type": "t", "text": "\n\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nMutations and rearrangements of RARS1 have been associated with a spectrum of human diseases. Biallelic variants in RARS1 underlie hypomyelinating leukodystrophies and Pelizaeus–Merzbacher–like disease, where altered enzyme function or reduced protein abundance leads to inefficient protein synthesis and impaired myelin formation. Distinct pathogenic mechanisms have been described—from amino acid substitutions that disrupt catalytic activity to mutations that introduce upstream open reading frames causing translational suppression. In addition, fusion events such as RARS‑MAD1L1 have been identified in nasopharyngeal carcinoma, where the aberrant protein promotes cell proliferation, enhances cancer stem cell–like properties, and confers chemoradioresistance through activation of the FUBP1/c‑Myc pathway. Furthermore, RARS1 influences the processing and secretion of cytokine precursors, thereby potentially contributing to neurodegenerative and inflammatory pathologies."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "11"}]}, {"type": "t", "text": "\n\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its conventional role in protein synthesis, RARS1 also participates in intricate protein–protein networks that modulate additional cellular processes. Its appended domains are critical for interactions with other synthetases—such as the leucyl-tRNA synthetase—ensuring proper assembly and function of the MSC. Moreover, overexpression of RARS1 has been shown to alter the secretion and proteolytic processing of cytokine precursors (for example, pro‑endothelial monocyte‑activating polypeptide II), linking its activity to pathways that govern neuronal integrity and tumor behavior. In contrast to mitochondrial aminoacyl‑tRNA synthetases—which display unique sub‑mitochondrial localizations dictated by hydrophobic and electrostatic interactions—the cytoplasmic localization of RARS1 underscores its specialized role in eukaryotic translation and cellular regulation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}, {"type": "fg_f", "ref": "6"}, {"type": "fg_f", "ref": "13"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Fang Yang, Xian Xia, Hui-Yan Lei, et al. 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