Project description:The ability to genetically encode noncanonical amino acids (ncAAs) has empowered proteins with improved or novel properties. However, existing strategies in mammalian cells rely on the introduction of blank codon for incorporating ncAAs, which is very inefficient and limits their widespread applications. Here, we develop a rare codon recoding strategy that takes advantage of the relative rarity of the TCG codon to achieve highly selective and efficient ncAA incorporation through systematic engineering and big data model predictions. We highlight the broad utility of this strategy for the incorporation of dozens of ncAAs into various functional proteins at the wild-type protein expression levels, as well as the synthesis of proteins with up to 6-site ncAAs or 4 distinct ncAAs in mammalian cells for downstream applications.
Project description:The ability to genetically encode noncanonical amino acids (ncAAs) has empowered proteins with improved or novel properties. However, existing strategies in mammalian cells rely on the introduction of blank codon for incorporating ncAAs, which is very inefficient and limits their widespread applications. Here, we develop a rare codon recoding strategy that takes advantage of the relative rarity of the TCG codon to achieve highly selective and efficient ncAA incorporation through systematic engineering and big data model predictions. We highlight the broad utility of this strategy for the incorporation of dozens of ncAAs into various functional proteins at the wild-type protein expression levels, as well as the synthesis of proteins with up to 6-site ncAAs or 4 distinct ncAAs in mammalian cells for downstream applications.
Project description:In order to systematically assess the frequency and origin of stop codon recoding events, we designed a library of reporters. We introduced premature stop codons into mScarlet that enabled high-throughput quantification of protein synthesis termination errors in E. coli using fluorescent microscopy. We found that under stress conditions, stop codon recoding may occur with a rate as high as 80%, depending on the nucleotide context, suggesting that evolution frequently samples stop codon recoding events. The analysis of selected reporters by mass spectrometry and RNA-seq showed that not only translation but also transcription errors contribute to stop codon recoding. The RNA polymerase is more likely to misincorporate a nucleotide at premature stop codons. Proteome-wide detection of stop codon recoding by mass spectrometry revealed that temperature regulates the expression of cryptic sequences generated by stop codon recoding in E. coli. Overall, our findings suggest that the environment influences the accuracy of protein production which increases protein heterogeneity when the organisms need to adapt to new conditions.
Project description:Stop codon recoding events give rise to longer proteins, which may alter the proteins function and thereby generate short-lasting phenotypic variability from a single gene.
In order to systematically assess the frequency and origin of recoding events, we designed a library of reporters. We introduced premature stop codons into mScarlet that enabled high-throughput quantification of protein synthesis termination errors in E.coli using fluorescent microscopy. We found that under stress conditions, stop codon recoding may occur as high as 80 percent of the time, depending on the genetic context, suggesting that evolution frequently samples stop codon recoding events. Targeted mass spectrometry and RNA-seq analyses showed that not only translational but also transcriptional errors contribute to stop codon recoding. The RNA polymerase is more likely to misincorporate a nucleotide at premature stop codons. Proteome-wide mass -spectrometry revealed that temperature regulates the expression of cryptic peptides generated by stop codon recoding in E.coli.
Overall, our findings suggest that the environment influences the accuracy of protein production which increases protein heterogeneity when the organisms need to adapt to new conditions.
Project description:Pseudouridine (Ψ) is known for decades, but its flexibility in base-pairing remains unclear. This study engineers artificial box H/ACA guide RNAs to direct pseudouridylation at the uridine of a premature termination codon (PTC; UAA, UAG, or UGA) within an intron-less mRNA and U36 of the anticodon of a matching tRNA in yeast and human cells. Targeted pseudouridylation leads to the formation of a Ψ-Ψ codon-anticodon pair, which, together with the other two Watson-Crick base pairs in the codon-anticodon duplex, significantly improves codon-anticodon recognition, robustly promoting PTC read-through. The intron-less mRNA level remains unchanged with or without guide RNAs. Additionally, pseudouridylation does not impact tRNA stability or charging. Our results show that nonsense suppression is promoted by the high affinity of the Ψ-Ψ pair, which is verified by melting curve analysis. This work has identified an unusual Ψ-Ψ base pair, which contributes significantly to codon-anticodon recognition and translational recoding.
Project description:Site-specific incorporation of two noncanonical amino acids for two-color bioorthogonal labeling and chemical-controlled crosslinking of proteins on live mammalian cells