MRPL48

MRPL48 (mL48) is a protein component of the mitochondrial large ribosomal subunit that participates in mitochondrial translation (PMID:32812867). Within the mitoribosome, mL48 acts together with mL40 and mL64 to coordinate translocation of mt-tRNA during the elongation cycle (PMID:32812867). Its C-terminal location near the mitoribosome surface places it in contact with the C-terminal tail of Oxa1L, linking the elongating ribosome to the co-translational membrane insertion of mitochondrially synthesized proteins (PMID:20601428). Loss of MRPL48 by CRISPR-Cas9 knockout sensitizes colorectal cancer cells to cetuximab, identifying it as a mediator of cetuximab resistance, though the molecular pathway connecting mitochondrial translation to drug response has not been characterized in the available corpus (PMID:33048115).

1. 2010 Medium

   Establishing how nascent mitochondrial proteins are handed from the ribosome to the membrane insertase, this work showed the Oxa1L C-terminal tail physically engages MRPL48 on the large subunit, positioning it at the ribosome-insertase interface.

   Evidence Chemical cross-linking with mass spectrometry and ribosome-binding assays using purified Oxa1L-CTT

   PMID:20601428

   Open questions at the time

   • Cross-linking alone does not define a direct binary interaction versus proximity within the assembled subunit
   • Functional consequence of disrupting the MRPL48-Oxa1L contact for membrane insertion not tested
   • Whether mL49 and mL51 or mL48 forms the principal contact is unresolved
2. 2020 High

   Resolving the structural role of mL48 in active translation, high-resolution cryo-EM of functional mitoribosome states placed mL48 with mL40 and mL64 at a site coordinating mt-tRNA translocation during elongation.

   Evidence Cryo-EM structure determination of human mitoribosome in eight functional complexes with mt-mRNA, mt-tRNAs and trans factors

   PMID:32812867

   Open questions at the time

   • Structural assignment does not define the kinetic contribution of mL48 to translocation
   • No mutational test of mL48's role in tRNA handling
3. 2020 Medium

   Connecting mitoribosomal function to a cancer drug response, knockout of MRPL48 was shown to enhance cetuximab sensitivity, implicating it in cetuximab resistance of colorectal cancer cells.

   Evidence CRISPR-Cas9 knockout in Caco-2 cells with colony formation and CCK-8 viability assays

   PMID:33048115

   Open questions at the time

   • No molecular pathway links mitochondrial translation to cetuximab response
   • Phenotype shown in a single cell line without in vivo validation
   • Whether the effect depends on mL48's translational role is untested

• How mL48's role in mt-tRNA translocation and its contact with Oxa1L mechanistically connect to cetuximab resistance remains unknown.
• No mechanistic bridge between mitochondrial translation defects and EGFR-pathway drug sensitivity established
• No structural or functional consequence of mL48 loss on co-translational membrane insertion demonstrated