Automated smFRET microscope for the quantification of label-free DNA oligos

Ribozyme synthesis of both L- and D- amino acid oligos

The ribosome is responsible for assembling proteins using 20 naturally occurring L-handed amino acids. However, incorporating non-natural amino acids into a protein is a challenging process needs improvement. In this study, we report a new possible approach to creating nonnatural peptides using ribozymes inspired by the peptidyl transfer center. These RNA scaffolds, which are approximately 100 nucleotides in length, bind to RNase T1 truncated tRNA-like chimeras and bring them into close proximity to facilitate peptide ligation. We used single-molecule fluorescence resonance energy transfer (smFRET) to show close distances between RNA-RNA, tRNALys-tRNALys, and RNA-tRNALys pairs, which strongly suggests that the mechanism of peptide ligation is due to the proximity of the substrate through dimerization of the enzymes. Mass spectrometry analysis confirmed the detection of oligopeptides from four amino acids, including L-Lysine, D-Lysine, L-Phenylalanine, and D-Phenylalanine. These results indicate that ribozymes have greater flexibility in accommodating nonnatural amino acids. Our findings pave the way for potentially new avenues in the synthesis of nonnatural peptides, beyond the limitations of ribosomal peptide synthesis and other existing methods.

smFRET study of rRNA dimerization at the peptidyl transfer center

The ribosome is a ribozyme. At the peptidyl transfer center (PTC) of 180 nt, two loops (the A- and P- loops) bind to tRNAs and position them in close proximity for efficient peptidyl ligation. There is also a 2-fold rotational symmetry in the PTC, which suggests that the precursor of the modern ribosome possibly emerged through dimerization and gene fusion. However, experiments that demonstrate the possible dimerization have not yet been published. In our investigation, we reported single molecule FRET studies of two RNA fragments that generated high FRET values. By dye-labeling the 5'-biotinylated rRNA molecules at the 3'- terminals, or labeling three different types of tRNA-like oligos, we observed that RNA scaffolds can assemble and bring several short tRNA-acceptor-domain analogs, but not full-length tRNAs, to close proximity. Mg2+ and continuous 3-way junction motifs are essential to this process, but amino acid charging to the tRNA analogs is not required. We observed RNA dimers via native gel-shifting experiments. These experiments support the possible existence of a proto-ribosome in the form of an RNA dimer or multimer.

Protein-free ribosomal RNA scaffolds can assemble poly-lysine oligos from charged tRNA fragments

Ribosomal protein synthesis is a central process of the modern biological world. Because the ribosome contains proteins itself, it is very important to understand its precursor and evolution. Small ribozymes have demonstrated the principle of "RNA world" hypothesis, but protein free peptide ligase remains elusive. In this report, we have identified two fragments in the peptidyl transfer center that can synthesize a 9-mer poly-lysine in a solution contains Mg²⁺. This result is deduced from isotope-shifting in high resolution MS. To our best knowledge, this is the longest peptide oligo that can be synthesized by a pure ribozyme. Via single molecule FRET experiments, we have demonstrated the ligase mechanism was probably by substrate proximity via dimerization. We prospect that these RNA fragments can be useful to synthesize template free natural and non-natural peptides, to be model system for peptidyl transfer reaction mechanism and can shed light to the evolution of ribosome.