Project description:In eukaryotes, up to one-third of cellular proteins are targeted to the endoplasmic reticulum, where they undergo folding, processing, sorting and trafficking to subsequent endomembrane compartments. Targeting to the endoplasmic reticulum has been shown to occur co-translationally by the signal recognition particle (SRP) pathway or post-translationally by the mammalian transmembrane recognition complex of 40 kDa (TRC40) and homologous yeast guided entry of tail-anchored proteins (GET) pathways. Despite the range of proteins that can be catered for by these two pathways, many proteins are still known to be independent of both SRP and GET, so there seems to be a critical need for an additional dedicated pathway for endoplasmic reticulum relay. We set out to uncover additional targeting proteins using unbiased high-content screening approaches. To this end, we performed a systematic visual screen using the yeast Saccharomyces cerevisiae, and uncovered three uncharacterized proteins whose loss affected targeting. We suggest that these proteins work together and demonstrate that they function in parallel with SRP and GET to target a broad range of substrates to the endoplasmic reticulum. The three proteins, which we name Snd1, Snd2 and Snd3 (for SRP-independent targeting), can synthetically compensate for the loss of both the SRP and GET pathways, and act as a backup targeting system. This explains why it has previously been difficult to demonstrate complete loss of targeting for some substrates. Our discovery thus puts in place an essential piece of the endoplasmic reticulum targeting puzzle, highlighting how the targeting apparatus of the eukaryotic cell is robust, interlinked and flexible.
Project description:The unfolded protein response (UPR) is a network of intracellular signaling pathways that supports the ability of the secretory pathway to maintain equilibrium between the load of proteins entering the endoplasmic reticulum (ER) and the protein folding capacity of the ER lumen. Current evidence suggests that human pathogenic fungi rely heavily on this pathway for virulence, but there is limited understanding of the mechanisms involved. The best known functional output of the UPR is transcriptional upregulation of mRNAs involved in ER homeostasis. However, this does not take into account mechanisms of translational regulation that involve differential recruitment of mRNAs to ribosomes. In this study, a global analysis of transcript-specific translational regulation was performed in the pathogenic mold Aspergillus fumigatus to determine the nature and scope of the translational response to ER stress.
Project description:Endoplasmic reticulum oxidoreductase 1 alpha (ERO1α) is an endoplasmic reticulum stress–related gene, which improves cell perseverance against challenges of high levels of protein misfolding during endoplasmic reticulum stress by retaining good activity of oxidative protein folding. Numerous studies have shown abnormal expression of ERo1α in various diseases, but its downstream target are not fully understood. Our work will help in the elucidation of the downstream molecular mechanism of ERO1α.
Project description:Localized protein synthesis is a fundamental mechanism for creating distinct subcellular environments. Here we developed a generalizable proximity-specific ribosome profiling strategy that enables global interrogation of translation in defined subcellular locations. We applied this approach to the endoplasmic reticulum (ER) in yeast and mammals. We observed the vast majority of secretory proteins to be co-translationally translocated, including substrates capable of post-translational insertion in vitro. Distinct translocon complexes engaged nascent chains at different points during synthesis. Whereas most proteins engaged the ER immediately following or even before signal sequence (SS) emergence, a class of Sec66-dependent proteins entered with a looped SS conformation. Finally, we observed rapid ribosome exchange into the cytosol following translation termination. These data provide insights into how distinct translocation mechanisms act in concert to promote efficient co-translational recruitment.
Project description:Non-coding 7SL RNA is an ancestor to mammalian Alu and B1 SINE RNAs and is thought to function exclusively within the Signal Recognition Particle (SRP), aiding in the translocation of secretory proteins into the endoplasmic reticulum for export. Here, we discover a surprising new function unrelated to protein secretion. Under acute heat shock, 7SL and SRP together selectively arrest cellular transcription and translation machineries as a crucial early response to stress. Under thermal stress, 7SL is upregulated, localizes to the nucleus, and binds to target genes repressed by heat shock. Concurrently, in the cytosol, SRP binds to ribosomes and inhibits new protein synthesis. Translational suppression occurs independently of the signal peptide and is abrogated by depleting SRP. Intriguingly, translation inhibition extends to the mitochondria, as nuclear-encoded mitochondrial genes are enriched among SRP targets. Thus, apart from its role in protein export, 7SL/SRP orchestrates a global response to acute stress that encompasses the nucleus, cytosol, and mitochondria across transcription and translation.
Project description:Non-coding 7SL RNA is an ancestor to mammalian Alu and B1 SINE RNAs and is thought to function exclusively within the Signal Recognition Particle (SRP), aiding in the translocation of secretory proteins into the endoplasmic reticulum for export. Here, we discover a surprising new function unrelated to protein secretion. Under acute heat shock, 7SL and SRP together selectively arrest cellular transcription and translation machineries as a crucial early response to stress. Under thermal stress, 7SL is upregulated, localizes to the nucleus, and binds to target genes repressed by heat shock. Concurrently, in the cytosol, SRP binds to ribosomes and inhibits new protein synthesis. Translational suppression occurs independently of the signal peptide and is abrogated by depleting SRP. Intriguingly, translation inhibition extends to the mitochondria, as nuclear-encoded mitochondrial genes are enriched among SRP targets. Thus, apart from its role in protein export, 7SL/SRP orchestrates a global response to acute stress that encompasses the nucleus, cytosol, and mitochondria across transcription and translation.
Project description:Non-coding 7SL RNA is an ancestor to mammalian Alu and B1 SINE RNAs and is thought to function exclusively within the Signal Recognition Particle (SRP), aiding in the translocation of secretory proteins into the endoplasmic reticulum for export. Here, we discover a surprising new function unrelated to protein secretion. Under acute heat shock, 7SL and SRP together selectively arrest cellular transcription and translation machineries as a crucial early response to stress. Under thermal stress, 7SL is upregulated, localizes to the nucleus, and binds to target genes repressed by heat shock. Concurrently, in the cytosol, SRP binds to ribosomes and inhibits new protein synthesis. Translational suppression occurs independently of the signal peptide and is abrogated by depleting SRP. Intriguingly, translation inhibition extends to the mitochondria, as nuclear-encoded mitochondrial genes are enriched among SRP targets. Thus, apart from its role in protein export, 7SL/SRP orchestrates a global response to acute stress that encompasses the nucleus, cytosol, and mitochondria across transcription and translation.