RPL36AL

RPL36AL is a ubiquitously expressed large-subunit ribosomal protein of the L44e/L36a family that functions at the E-site of human 80S ribosomes during translation termination (PMID:19647033, PMID:25191528). It originated as an intronless, autosomally retrotransposed copy of the X-linked progenitor RPL36A and shares 92–99% amino acid identity with it (PMID:12490704). Within the ribosome, RPL36AL makes direct zero-length contact with the CCA end (C74, C75, A76) of deacylated tRNA positioned at the P/E hybrid site, with its Lys53 lying adjacent to the terminal A76, and it binds deacylated tRNA with nanomolar affinity through an interface extending from the CCA end to the tRNA elbow (PMID:19647033, PMID:22865768, PMID:25191528). The protein carries seven monomethylated residues and a conserved GGQ motif (at Q51) characteristic of L44e proteins and shared with the peptidyl-tRNA hydrolysis motif of release factors (PMID:22865768). During termination, RPL36AL forms a ternary complex with P-site tRNA and the release factor eRF1 at the peptidyl transferase center; eRF1 binding to a stop codon at the A-site induces an alternative ribosome/tRNA conformation that switches the tRNA crosslink from RPL36AL to RPL37 in a mutually exclusive manner (PMID:25191528).

1. 2002 Medium

   Established that RPL36AL is a bona fide functional ribosomal protein gene rather than a processed pseudogene, distinguishing it from tissue-restricted paralogs and setting it as the ubiquitous L36a-type product.

   Evidence Northern blot, PCR, and gene-structure sequence analysis defining its intronless retrotransposed origin and ubiquitous expression

   PMID:12490704

   Open questions at the time

   • Functional role within the ribosome not addressed
   • Whether it is differentially incorporated relative to the X-linked progenitor RPL36A not tested
2. 2009 High

   Resolved where RPL36AL acts on the ribosome by showing it directly contacts the CCA end of P-site tRNA, placing it at the tRNA-binding core of the large subunit.

   Evidence Periodate-oxidized tRNA zero-length crosslinking with intact-tRNA competition control and mass spectrometry identification in human 80S ribosomes

   PMID:19647033

   Open questions at the time

   • Exact tRNA-binding site (P vs P/E) not yet pinpointed
   • Functional consequence of the contact unknown
3. 2012 High

   Refined the contact to the P/E hybrid site and identified the specific residues and modifications involved, revealing a conserved GGQ motif that links RPL36AL to release-factor-type hydrolysis chemistry.

   Evidence Positional crosslinking with site specificity controls and MS-based mapping of Lys53 contact and seven monomethylated residues including Q51 of the GGQ motif

   PMID:22865768

   Open questions at the time

   • Catalytic significance of the GGQ motif in RPL36AL not functionally demonstrated
   • Roles of the individual methylations not tested
4. 2014 High

   Connected RPL36AL to translation termination by demonstrating a ternary complex with eRF1 and P-site tRNA and an eRF1-induced conformational switch that hands the tRNA contact to RPL37.

   Evidence Recombinant tRNA-affinity binding assay, programmed 80S ribosome reconstitution with eRF1, zero-length crosslinking, and structural modeling on the archaeal RPL44E ortholog

   PMID:25191528

   Open questions at the time

   • No high-resolution structure of the human RPL36AL–tRNA–eRF1 complex
   • Mechanistic contribution of RPL36AL to peptidyl-tRNA hydrolysis not directly measured

• Whether RPL36AL's GGQ motif and methylations actively contribute to termination catalysis, and how the RPL36AL-to-RPL37 conformational switch is coupled to peptide release, remain unresolved.
• No functional assay of RPL36AL GGQ-motif mutants in termination
• No cryo-EM structure of the eRF1-bound termination intermediate
• Cellular phenotype of RPL36AL loss uncharacterized