Project description:We developed an efficient, cost-effective assay for Structural Inference By Structure-stability-based selection of deep mutation variants and high throughput sequencing (Sibs-Seq). We demonstrated that unlike naturally occurring homologous sequences evolved over billions of years, these stability-selected, artificial homologs in a single-round 24 or 36 hours of mutation selections is often sufficient for producing high-accuracy structure prediction with < 2 angstrom root-mean-squared deviation (RMSD) to the native structure.
Project description:In humans, the 813 G protein-coupled receptors (GPCRs) are responsible for transducing diverse chemical stimuli to alter cell state, and are the largest class of drug targets. Their myriad structural conformations and various modes of signaling make it challenging to understand their structure and function. Here we developed a platform to characterize large libraries of GPCR variants in human cell lines with a barcoded transcriptional reporter of G-protein signal transduction. We tested 7,800 of 7,828 possible single amino acid substitutions to the beta-2 adrenergic receptor (β2AR) at four concentrations of the agonist isoproterenol. We identified residues specifically important for β2AR signaling, mutations in the human population that are potentially loss of function, and residues that modulate basal activity. Using unsupervised learning, we resolve residues critical for signaling, including all major structural motifs and molecular interfaces. We also find a previously uncharacterized structural latch spanning the first two extracellular loops that is highly conserved across Class A GPCRs and is conformationally rigid in both the inactive and active states of the receptor. More broadly, by linking deep mutational scanning with engineered transcriptional reporters, we establish a generalizable method for exploring pharmacogenomics, structure and function across broad classes of drug receptors.
Project description:Decoding post-transcriptional regulatory programs underlying gene expression is a crucial step toward a predictive dynamical understanding of cellular state transitions. Despite recent systematic efforts, the sequence determinants of such mechanisms remain largely uncharacterized. An important obstacle in revealing these elements stems from the contribution of local secondary structures in defining interaction partners in a variety of regulatory contexts, including but not limited to transcript stability, alternative splicing and localization. There are many documented instances where the presence of a structural regulatory element dictates alternative splicing patterns (e.g. human cardiac troponin T) or affects other aspects of RNA biology. Thus, a full characterization of post-transcriptional regulatory programs requires capturing information provided by both local secondary structures and the underlying sequence. We have developed a computational framework based on context-free grammars and mutual information that systematically explores the immense space of structural elements and reveals motifs that are significantly informative of genome-wide measurements of RNA behavior. The application of this framework to genome-wide mammalian mRNA stability data revealed eight highly significant elements with substantial structural information, for the strongest of which we showed a major role in global mRNA regulation. Through biochemistry, mass-spectrometry, and in vivo binding studies, we identified HNRPA2B1 as the key regulator that binds this element and stabilizes a large number of its target genes. Ultimately, we created a global post-transcriptional regulatory map based on the identity of the discovered linear and structural cis-regulatory elements, their regulatory interactions and their target pathways. This approach can also be employed to reveal the structural elements that modulate other aspects of RNA behavior. This SuperSeries is composed of the following subset Series: GSE35749: sRSM1 synthetic decoy vs. scrambled transfections in MDA-MB-231 cells GSE35753: HNRPA2B1 RIP-chip GSE35756: Whole-genome decay rate measurements in MDA-MB-231 cells transfected with HNRPA2B1 siRNAs versus controls GSE35757: siRNA-mediated HNRPA2B1 knock-down in MDA-MB-231 cells GSE35799: HNRPA2B1 HITS-CLIP Refer to individual Series
Project description:RNA mutations are known to change mobility in native gels. What is not known is if mobility can serve as an effective tool to separate structurally similar (structural homologs) from structurally destabilized variants in a deep-mutation library of an RNA. Here we defined the proportion of a mutant in the native band from native polyacrylamide gel electrophoresis (PAGE) as a native-mobility-fitness score. The fitness scores of single and double mutants allowed a unsupervised, RNA-specific analysis to detect key secondary and tertiary base pairs through covariational signals. Subsequent amplification of these signals and their use as restraints for folding led to not only high-accuracy secondary structures with the F1-score > 0.9, but also quality tertiary-structure models between 3.6 Å and 7.7 Å RMSD from their native structures for the best in top 5 models for 6 RNAs tested including two CASP 15 difficult targets. This MobiSeq method should provide a simple and effective method for inferring 2D and 3D structures and improving mechanistic understanding of all structured RNAs.
Project description:Decoding post-transcriptional regulatory programs underlying gene expression is a crucial step toward a predictive dynamical understanding of cellular state transitions. Despite recent systematic efforts, the sequence determinants of such mechanisms remain largely uncharacterized. An important obstacle in revealing these elements stems from the contribution of local secondary structures in defining interaction partners in a variety of regulatory contexts, including but not limited to transcript stability, alternative splicing and localization. There are many documented instances where the presence of a structural regulatory element dictates alternative splicing patterns (e.g. human cardiac troponin T) or affects other aspects of RNA biology. Thus, a full characterization of post-transcriptional regulatory programs requires capturing information provided by both local secondary structures and the underlying sequence. We have developed a computational framework based on context-free grammars and mutual information that systematically explores the immense space of structural elements and reveals motifs that are significantly informative of genome-wide measurements of RNA behavior. The application of this framework to genome-wide mammalian mRNA stability data revealed eight highly significant elements with substantial structural information, for the strongest of which we showed a major role in global mRNA regulation. Through biochemistry, mass-spectrometry, and in vivo binding studies, we identified HNRPA2B1 as the key regulator that binds this element and stabilizes a large number of its target genes. Ultimately, we created a global post-transcriptional regulatory map based on the identity of the discovered linear and structural cis-regulatory elements, their regulatory interactions and their target pathways. This approach can also be employed to reveal the structural elements that modulate other aspects of RNA behavior. This SuperSeries is composed of the SubSeries listed below.
Project description:N6-methyladenosine (m6A) is the most prevalent internal modification of mammalian messenger RNAs (mRNAs) and long non-coding RNAs. The biological functions of this reversible RNA modification can be interpreted by cytoplasmic and nuclear "m6A reader" proteins to fine-tune gene expression, such as mRNA degradation and translation initiation. Here we profiled transcriptome-wide m6A sites in adult mouse cerebral cortex, underscoring that m6A is a widespread epitranscriptomic modification in brain. Interestingly, the mRNA targets of fragile X mental retardation protein (FMRP), a selective RNA-binding protein, are enriched for m6A marks. Loss of functional FMRP leads to Fragile X syndrome (FXS), the most common inherited form of intellectual disability. Transcriptome-wide gene expression profiling identified 2,035 genes differentially expressed in the absence of FMRP in cortex, and 92.5% of 174 downregulated FMRP targets are marked by m6A. Biochemical analyses indicate that FMRP binds to the m6A sites of its mRNA targets and interacts with m6A reader YTHDF2 in an RNA-independent manner. FMRP maintains the stability of its mRNA targets while YTHDF2 promotes the degradation of these mRNAs. These data together suggest that FMRP regulates the stability of its m6A-marked mRNA targets through YTHDF2, which could potentially contribute to the molecular pathogenesis of FXS.
Project description:Alternative polyadenylation generates numerous 3' mRNA isoforms per gene; regulation of this process is critical in development and impaired in cancer. Individual isoforms from the same gene can vary greatly in biological properties such as translational efficiency, localization, and half-life. Even closely related isoforms - including those differing by a single nt - can have different biological properties, but the underlying mechanisms are unknown. Here we show that many highly similar yeast isoforms unexpectedly exhibit extensive structural variation and differential Pab1 binding, and that these physical properties serve as a good predictor of relative isoform stability. We developed DREADS, a dimethyl sulphate (DMS)-based technique, to obtain the first transcriptome-scale structural description of individual 3' mRNA isoforms in vivo. Strikingly, near-identical yeast mRNA isoforms arising from the same gene can possess dramatically different DMS modification profiles over hundreds of nt upstream of the poly(A) tail. DREADS analyses of the same mRNAs refolded in vitro or in different species indicate that structural differences in vivo are often due to trans- acting factors. CLIP-READS, a technique we developed to measure isoform-specific binding, reveals that differences in Poly(A) binding protein (Pab1) binding to 3' ends correlate with the extent of structural variation for closely-spaced isoforms. A pattern encompassing single-strandedness near the 3' terminus, double-stranded character of the poly(A) tail, and low Pab1 binding is significantly associated with mRNA stability. Sequences responsible for isoform-specific structures, differential Pab1 binding, and mRNA stability are evolutionarily conserved, and are indicative of biological function.