Proteins, the workhorses of the cell, orchestrate all cellular processes from division to death. However, to perform these critical roles and prevent pathological functions, optimal protein levels must be achieved by balancing synthesis by ribosomes and degradation by proteasomes. Ribosomal protein synthesis is tightly regulated to ensure the generation of fully functional proteins. Ribosomal quality control (RQC) pathways identify and respond to disruptions in protein translation, such as ribosomal stalling. Such stalling on the mRNA recruits specific E3 ubiquitin ligases to 'tag’ ribosomal components and release the stalled ribosome. This prevents the synthesis of dysfunctional protein products, which are often associated with diseases including Cystic Fibrosis and Hurler Syndrome. The understudied E3 ubiquitin ligase, RNF14, is implicated in a novel RQC pathway where it induces degradation of translation factors associated with stalled ribosomes [1]. However, the mechanism of how RNF14 tags these factors, and the resulting downstream signalling remains enigmatic.
To address these shortcomings, we’ve used a combination of in vitro reconstituted systems, structural biology, mass spectrometry and cell-based assays to show that, upon inducing ribosomal stalling by specific drugs, RNF14 generates unconventional, branched ubiquitin chains in vitro and in cells. Given this unusual specificity we are now investigating the mechanism by which RNF14 regulates ribosomal quality control pathways and its downstream signalling functions. Ultimately, understanding this process will provide insight into the pathogenesis of diseases caused by truncated proteins and may lead to novel therapeutic options.