Nucleoside modifications in RNA limit activation of 2′-5′-oligoadenylate synthetase and increase resistance to cleavage by RNase L

The interferon-induced enzymes 2′-5′-oligoadenylate synthetase (OAS) and RNase L are key components of innate immunity involved in sensory and effector functions following viral infections. Upon binding target RNA, OAS is activated to produce 2′-5′-linked oligoadenylates (2-5A) that activate RNase L, which then cleaves single-stranded self and non-self RNA. Modified nucleosides that are present in cellular transcripts have been shown to suppress activation of several RNA sensors. Here, we demonstrate that in vitro transcribed, unmodified RNA activates OAS, induces RNase L-mediated ribosomal RNA (rRNA) cleavage and is rapidly cleaved by RNase L. In contrast, RNA containing modified nucleosides activates OAS less efficiently and induces limited rRNA cleavage. Nucleoside modifications also make RNA resistant to cleavage by RNase L. Examining translation in RNase L−/− cells and mice confirmed that RNase L activity reduces translation of unmodified mRNA, which is not observed with modified mRNA. Additionally, mRNA containing the nucleoside modification pseudouridine is translated longer and has an extended half-life. The observation that modified nucleosides in RNA reduce 2-5A pathway activation joins OAS and RNase L to the list of RNA sensors and effectors whose functions are limited when RNA is modified, confirming the role of nucleoside modifications in suppressing immune recognition of RNA

Synthetic Biology of Proteins: Tuning GFPs Folding and Stability with Fluoroproline

Proline residues affect protein folding and stability via cis/trans isomerization of peptide bonds and by the C(gamma)-exo or -endo puckering of their pyrrolidine rings. Peptide bond conformation as well as puckering propensity can be manipulated by proper choice of ring substituents, e.g. C(gamma)-fluorination. Synthetic chemistry has routinely exploited ring-substituted proline analogs in order to change, modulate or control folding and stability of peptides.In order to transmit this synthetic strategy to complex proteins, the ten proline residues of enhanced green fluorescent protein (EGFP) were globally replaced by (4R)- and (4S)-fluoroprolines (FPro). By this approach, we expected to affect the cis/trans peptidyl-proline bond isomerization and pyrrolidine ring puckering, which are responsible for the slow folding of this protein. Expression of both protein variants occurred at levels comparable to the parent protein, but the (4R)-FPro-EGFP resulted in irreversibly unfolded inclusion bodies, whereas the (4S)-FPro-EGFP led to a soluble fluorescent protein. Upon thermal denaturation, refolding of this variant occurs at significantly higher rates than the parent EGFP. Comparative inspection of the X-ray structures of EGFP and (4S)-FPro-EGFP allowed to correlate the significantly improved refolding with the C(gamma)-endo puckering of the pyrrolidine rings, which is favored by 4S-fluorination, and to lesser extents with the cis/trans isomerization of the prolines.We discovered that the folding rates and stability of GFP are affected to a lesser extent by cis/trans isomerization of the proline bonds than by the puckering of pyrrolidine rings. In the C(gamma)-endo conformation the fluorine atoms are positioned in the structural context of the GFP such that a network of favorable local interactions is established. From these results the combined use of synthetic amino acids along with detailed structural knowledge and existing protein engineering methods can be envisioned as a promising strategy for the design of complex tailor-made proteins and even cellular structures of superior properties compared to the native forms

An Expanded Set of Amino Acid Analogs for the Ribosomal Translation of Unnatural Peptides

BACKGROUND: The application of in vitro translation to the synthesis of unnatural peptides may allow the production of extremely large libraries of highly modified peptides, which are a potential source of lead compounds in the search for new pharmaceutical agents. The specificity of the translation apparatus, however, limits the diversity of unnatural amino acids that can be incorporated into peptides by ribosomal translation. We have previously shown that over 90 unnatural amino acids can be enzymatically loaded onto tRNA. METHODOLOGY/PRINCIPAL FINDINGS: We have now used a competition assay to assess the efficiency of tRNA-aminoacylation of these analogs. We have also used a series of peptide translation assays to measure the efficiency with which these analogs are incorporated into peptides. The translation apparatus tolerates most side chain derivatives, a few alpha,alpha disubstituted, N-methyl and alpha-hydroxy derivatives, but no beta-amino acids. We show that over 50 unnatural amino acids can be incorporated into peptides by ribosomal translation. Using a set of analogs that are efficiently charged and translated we were able to prepare individual peptides containing up to 13 different unnatural amino acids. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that a diverse array of unnatural building blocks can be translationally incorporated into peptides. These building blocks provide new opportunities for in vitro selections with highly modified drug-like peptides

Single Sensillum responses in the male moth Adoxophyes orana (F.v.R.) to female sex pheromone components and their geometrical isomers

A technique is described for the recording of receptor and action potentials from the outer dendritic segments of the olfactory cells in individual antennalSensilla trichodea in insects. The 50 μm long olfactory hairs on the antennae of adult male summerfruit toftrix moth,Adoxophyes orana, are shown to possess two cells responsive to the female sex pheromone (a 9∶1 mixture ofcis-9 andcis-11-TDA (= tetradecen-1-ol acetate)). One of these cells (typeB) is sensitive tocis-9-TDA, the other (type A) mainly responds tocis-11-TDA and, to a much smaller extent, tocis-9-TDA. The behavioural inhibitorstrans-9 andtrans-11-TDA evoke small responses in both cells, which may have been caused by contamination of these substances by thecis isomers (Fig. 6). It appears that the pheromone receptor cells are not ‘tuned’ to the optimal 9∶1 mixture (Fig. 7). Hence, the attractiveness of the pheromone should be determined in the central nervous system by comparison of the responses from theA andB cells. A rough calculation indicates that the males are very well able to discriminate between different mixture ratios. It is suggested that thecis-9-/cis-11-TDA ratio excreted by the females shows a considerable variation