# AARSD1 notes

- Canonical AARSD1 is a translation-quality-control factor, not an alanine-tRNA ligase. Human AlaX is described as "exclusively distributed in the cytoplasm" and as "an active trans-editing factor with strict Ser-specificity" [PMID:38869066 Eukaryotic AlaX provides multiple checkpoints for quality and quantity of aminoacyl-tRNAs in translation, "human AlaX (hAlaX), which is exclusively distributed in the cytoplasm, is an active trans-editing factor with strict Ser-specificity"].
- Loss of AlaX causes mistranslation, which supports the BP terms around translational fidelity rather than aminoacylation [PMID:38869066 Eukaryotic AlaX provides multiple checkpoints for quality and quantity of aminoacyl-tRNAs in translation, "loss of ScAlaX or hAlaX readily induced Ala- and Thr-to-Ser misincorporation"].
- The broader vertebrate context is still translation proofreading in trans, but PMID:32484512 is about ThrRS cross-editing rather than direct AARSD1 biochemistry [PMID:32484512 Cross-editing by a tRNA synthetase allows vertebrates to abundantly express mischargeable tRNA without causing mistranslation, "while wrong amino acids are corrected within an aaRS, a wrong tRNA is handled in trans by an aaRS cognate to the mischarged tRNA species"].
- The HSP90 side is real literature, but it is muscle-specific and likely not about canonical AARSD1. The abstract says Aarsd1L is a "novel muscle-specific Hsp90 cochaperone" and that "Aarsd1L replaces the more ubiquitous cochaperone p23" during differentiation [PMID:26884463 A Remodeled Hsp90 Molecular Chaperone Ensemble with the Novel Cochaperone Aarsd1 Is Required for Muscle Differentiation, "only Hsp90β remains, which is the only isoform capable of interacting with the novel muscle-specific Hsp90 cochaperone Aarsd1L"; "During muscle differentiation, Aarsd1L replaces the more ubiquitous cochaperone p23"].
- UniProt strongly suggests that the cochaperone literature should not be generalized to the canonical proofreading isoform. The local UniProt export assigns the core function as proofreading and notes that isoforms 2 and 3 are based on readthrough transcripts that may produce PTGES3L-AARSD1 fusion proteins [file:human/AARSD1/AARSD1-uniprot.txt, "Functions in trans to edit the amino acid moiety from incorrectly charged tRNA(Ala)." / "Based on a readthrough transcript which may produce a PTGES3L-AARSD1 fusion protein."].
- NCBI treats PTGES3L-AARSD1 as a separate readthrough locus and explicitly says the readthrough transcript encodes a fusion protein; its conserved domains include a p23/HSP90-related module plus AlaX/editing domains [NCBI Gene 100885850 PTGES3L-AARSD1 readthrough, "The readthrough transcript encodes a fusion protein that shares sequence identity with each individual gene product." / "p23; p23 binds heat shock protein (Hsp)90"; "AlaX; Ser-tRNA(Ala) deacylase AlaX (editing enzyme)"].
- Working interpretation for review: PN translation placement is core and well supported. PN HSP90-cochaperone placement is explainable, but only as a contextual/readthrough-derived isoform story rather than as a general gene-level function of canonical AARSD1.
- The nucleus GO annotation is high-throughput sperm-nucleus proteomics only, so keep it contextual [PMID:21630459 Proteomic characterization of the human sperm nucleus, "403 different proteins have been identified from the isolated sperm nuclei"].

## Description cleanup note

The YAML `description` field was revised to keep it as a standalone biological summary. Project-specific curation framing moved here instead.

- Moved out of the YAML description: PN translation placement was interpreted as core biology, while the separate PN suggestion of HSP90 cochaperone function was not supported as a core gene-level assignment for canonical AARSD1.