The Ribosome and Beyond: Understanding the role of translational fidelity in rare genetic disorders

Abstract

With the increasing accessibility of patient genome sequencing, causative mutations for rare genetic diseases are being uncovered at an unprecedented rate. Among these are disorders resulting from mutations in protein synthesis machinery, including the ribosome and translation factors. Originally described in 1999, the accumulation of new information brings new questions regarding their tissue-specific and otherwise paradoxical nature. Explored here are investigations into two classes of genetic disorders, describing several novel diseases that illustrate the commonalities and differences between their classes. Specifically, two variants of RPL9 are shown to cause disparate clinical presentations despite both causing pre-rRNA processing defects, including Diamond Blackfan anemia (DBA) from a 5’UTR variant and multiple cancer incidences from a missense mutation. The 5’UTR variant is shown to result in haploinsufficiency and p53 activation, while the missense variant impairs translational fidelity because of defective stop codon recognition. Additionally, evidence is presented that correlates several de novo missense mutations in EEF2 to neurodevelopmental disorders, building on research connecting eEF2 dysfunction to neurological disease. These mutations are shown to also cause translational fidelity loss and implicate eEF2-ribosome interactions in reading frame maintenance. All of the disease-causing mutants of eEF2 were found to map to sites of interaction with critical features of ribosomal RNA. These eEF2 sites of ribosome contact were further investigated using a panel of rationally designed mutations intended to probe the relationships between biophysical interactions of eEF2 and the ribosome, and biological function. These mutants exhibited translational fidelity defects and were demonstrated to have lower catalytic activity in vitro. Overall, this work highlights salient points about ribosomopathies and translationopathies, their molecular mechanisms, and the relevance of translational fidelity to human health.