RPL8

RPL8 (uL2) is a structural protein of the 60S large ribosomal subunit essential for ribosome production, and human loss-of-function missense variants impair ribosome biogenesis and cause Diamond-Blackfan anemia (PMID:34961992). Its function centers on an unstructured C-terminal loop that contacts 28S rRNA helix H93 near the peptidyl transferase center; a eukaryote-specific hydroxylation of His216 within this loop stabilizes a binding-competent conformation, and uL2 engagement of H93 induces structural rearrangements at universally conserved nucleotides adjacent to the PTC (PMID:25702831). The His216 hydroxylation is installed by the JmjC-domain hydroxylase NO66, which recognizes an NHXH motif in the uL2 residue 204–224 region and requires oligomerization for efficient catalysis (PMID:26327385). The placement of uL2 during large-subunit assembly is tightly ordered: in bacteria the GTPase YsxC occupies the uL2 binding site in an assembly intermediate as a placeholder, controlling the timing of rRNA helix folding before uL2 itself binds and the surrounding helices mature (PMID:41148149).

1. 2015 Medium

   Established how uL2 contributes to peptidyl transferase center architecture and why a eukaryote-specific His216 modification matters, by showing the hydroxyl stabilizes the C-terminal loop conformation for H93 binding.

   Evidence Hydroxyl radical and chemical probing of an rRNA mimic comparing natural hydroxylated vs. recombinant unmodified uL2

   PMID:25702831

   Open questions at the time

   • Done on an rRNA segment mimic rather than intact 28S rRNA/assembled ribosome
   • Functional consequence of His216 hydroxylation for translation not measured
   • Single lab, in vitro binding readout
2. 2015 High

   Identified the enzyme and recognition logic for uL2 modification, defining NO66 as the His216 hydroxylase and the structural requirements for its catalysis.

   Evidence Crystal structure of NO66 bound to an Rpl8(204-224) peptide with in vitro hydroxylase assays, mutagenesis, and oligomerization analysis

   PMID:26327385

   Open questions at the time

   • Does not establish the cellular consequence of losing the modification
   • Whether hydroxylation is co- or post-assembly is unresolved
3. 2022 Medium

   Connected RPL8 directly to human disease, showing that deficient variants impair ribosome production and cause Diamond-Blackfan anemia.

   Evidence Functional assays of patient missense variants in patient-derived lymphoblastoid cells and yeast models

   PMID:34961992

   Open questions at the time

   • Specific step of ribosome biogenesis disrupted not pinpointed
   • Genotype-phenotype relationships across variants not detailed
4. 2025 High

   Resolved the timing and ordering of uL2 incorporation during large-subunit assembly, showing a GTPase placeholder controls rRNA folding before uL2 binds.

   Evidence Cryo-EM of a Bacillus subtilis 44.5S assembly intermediate bound to YsxC with biochemical assembly assays

   PMID:41148149

   Open questions at the time

   • Established in bacteria; conservation of an equivalent placeholder in eukaryotic 60S assembly not shown
   • Trigger for YsxC release and handoff to uL2 not defined

• Whether the reported pro-tumorigenic roles of RPL8 in hepatocellular carcinoma reflect a direct extra-ribosomal mechanism or downstream consequences of altered ribosome output remains unresolved.
• mTORC1 pathway placement rests on bioinformatics with only partial USF1 rescue, no direct biochemical interaction
• GSH/ferroptosis regulation lacks a defined molecular mechanism
• No link drawn between cancer phenotypes and the ribosome-assembly/PTC functions of uL2