MRPL28

MRPL28 (bL28m) is a structural component of the mitochondrial ribosomal large subunit that links mitochondrial protein synthesis to oxidative metabolism (PMID:19753307, PMID:28931599). Its yeast ortholog MrpL28 (mL40) assembles into a central-protuberance subcomplex of the mitoribosome together with MrpL35, MrpL7, Mrp7, MrpL36, and MrpL17, a subcomplex that coordinates Cox1 synthesis with cytochrome c oxidase assembly (PMID:28931599). Consistent with this role in sustaining the respiratory machinery, knockdown of MRPL28 in pancreatic tumor cells lowers mitochondrial activity and shifts metabolism toward glycolysis; this loss suppresses growth in vitro yet accelerates tumor growth in vivo, identifying MRPL28 as a modulator of oxygen consumption as a rate-limiting determinant of tumor proliferation (PMID:19753307). Beyond these findings, no further mechanistic detail has been characterized in the available corpus.

1. 2009 Medium

   Established that MRPL28 is a functional regulator of mitochondrial metabolism whose loss rewires the balance between oxidative phosphorylation and glycolysis with opposing effects on cell growth and tumor growth.

   Evidence shRNA knockdown in pancreatic tumor cells with in vitro growth, in vivo tumor growth, oxygen consumption, and glycolysis readouts

   PMID:19753307

   Open questions at the time

   • Did not define the molecular role of MRPL28 within the mitoribosome
   • Mechanism linking reduced mitochondrial activity to accelerated in vivo tumor growth not resolved
   • Single lab, single gene within a broader screen
2. 2017 Medium

   Defined the structural and functional context of MRPL28 by placing its yeast ortholog in a mitoribosomal central-protuberance subcomplex coupling Cox1 synthesis to COX assembly.

   Evidence Co-immunoprecipitation/subcomplex isolation in yeast with respiratory-defective mutant analysis and mitochondrial protein synthesis assays

   PMID:28931599

   Open questions at the time

   • Subcomplex membership and Cox1-coordination role shown in yeast, not confirmed in human mitoribosomes
   • Direct molecular mechanism by which the subcomplex coordinates translation with COX assembly not established
   • Connection between this structural role and the tumor metabolic phenotype not directly tested

• How the mitoribosomal structural role of MRPL28 mechanistically drives the metabolic and tumor-growth phenotypes in human cells remains unresolved.
• No human mitoribosome subcomplex characterization in the corpus
• No structural model of human MRPL28 in the timeline
• Causal link between Cox1/COX coordination and the glycolytic shift untested