GPN‐loop GTPases 1 and 3 are required for RNA polymerase II (RNAPII) nuclear import. Gpn1 and Gpn3 display some sequence similarity, physically associate, and their protein expression levels are mutually dependent in human cells. We performed here Fluorescence Resonance Energy Transfer (FRET), molecular modeling, and cell biology experiments to understand, and eventually disrupt, human Gpn1–Gpn3 interaction in live HEK293‐AD cells. Transiently expressed EYFP‐Gpn1 and Gpn3‐CFP generated a strong FRET signal, indicative of a very close proximity, in the cytoplasm of HEK293‐AD cells. Molecular modeling of the human Gpn1–Gpn3 heterodimer based on the crystallographic structure of Npa3, the Saccharomyces cerevisiae Gpn1 ortholog, revealed that human Gpn1 and Gpn3 associate through a large interaction surface formed by internal α‐helix 7, insertion 2, and the GPN‐loop from each protein. In site‐directed mutagenesis experiments of interface residues, we identified the W132D and M227D EYFP‐Gpn1 mutants as defective to produce a FRET signal when coexpressed with Gpn3‐CFP. Simultaneous but not individual expression of Gpn1 and Gpn3, with either or both proteins fused to EYFP, retained RNAPII in the cytoplasm and markedly inhibited global transcription in HEK293‐AD cells. Interestingly, the W132D and M227D Gpn1 mutants that showed an impaired ability to interact with Gpn3 by FRET were also unable to delocalize RNAPII in this assay, indicating that an intact Gpn1–Gpn3 interaction is required to display the dominant‐negative effect on endogenous Gpn1/Gpn3 function we described here. Altogether, our results suggest that a Gpn1–Gpn3 strong interaction is critical for their cellular function.
The pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected millions of people worldwide. Public health strategies to reduce viral transmission are based on widespread diagnostic testing to detect and isolate contagious patients. Several reverse transcription (RT)-PCR tests, along with other SARS-CoV-2 diagnostic assays, are available to attempt to cover the global demand. Loop-mediated isothermal amplification (LAMP) based methods have been established as rapid, accurate, point of care diagnostic tests for viral infections; hence, they represent an excellent alternative for SARS-CoV-2 detection. The aim of this study was to develop and describe molecular detection systems for SARS-CoV-2 based on RT-LAMP. Recombinant DNA polymerase from Bacillus stearothermophilus and thermostable engineered reverse transcriptase from Moloney Murine Leukemia Virus were expressed using a prokaryotic system and purified by fast protein liquid chromatography. These enzymes were used to set up fluorometric real time and colorimetric end-point RT-LAMP assays. Several reaction conditions were optimized such as reaction temperature, Tris-HCl concentration, and pH of the diagnostic tests. The key enzymes for RT-LAMP were purified and their enzymatic activity was determined. Standardized reaction conditions for both RT-LAMP assays were 65°C and a Tris-HCl-free buffer at pH 8.8. Colorimetric end-point RT-LAMP assay was successfully used for viral detection from clinical saliva samples with 100% sensitivity and 100% specificity compared to the results obtained by RT-qPCR based diagnostic protocols with Ct values until 30. The developed RT-LAMP diagnostic tests based on purified recombinant enzymes allowed a sensitive and specific detection of the nucleocapsid gene of SARS-CoV-2.
Triosephosphate isomerases (TPIs) from Taenia solium (TsTPI) and Schistosoma mansoni (SmTPI) are potential vaccine and drug targets against cysticercosis and schistosomiasis, respectively. This is due to the dependence of parasitic helminths on glycolysis and because those proteins elicit an immune response, presumably due to their surface localization. Here we report the crystal structures of TsTPI and SmTPI in complex with 2-phosphoglyceric acid (2-PGA). Both TPIs fold into a dimeric (β-α) 8 barrel in which the dimer interface consists of α-helices 2, 3, and 4, and swapping of loop 3. TPIs from parasitic helminths harbor a region of three amino acids knows as the SXD/E insert (S155 to E157 and S157 to D159 in TsTPI and SmTPI, respectively). This insert is located between α5 and β6 and is proposed to be the main TPI epitope. This region is part of a solvent-exposed 3 10 -helix that folds into a hook-like structure. The crystal structures of TsTPI and SmTPI predicted conformational epitopes that could be used for vaccine design. Surprisingly, the epitopes corresponding to the SXD/E inserts are not the ones with the greatest immunological potential. SmTPI, but not TsTPI, habors a sole solvent exposed cysteine (SmTPI-S230) and alterations in this residue decrease catalysis. The latter suggests that thiol-conjugating agents could be used to target SmTPI. In sum, the crystal structures of SmTPI and TsTPI are a blueprint for targeted schistosomiasis and cysticercosis drug and vaccine development.
Author summaryBecause of the worldwide prevalence of schistosomiasis and cysticercosis, it is critical to develop drugs and vaccines against their causative agents. The glycolytic enzyme triosephosphate isomerase (TPI) is a dual-edged sword against diseases caused by parasitic helminths. This is because helminths heavily depend on glycolysis for energy and because the PLOS Neglected Tropical Diseases | https://doi.
Gpn3 is required for RNA polymerase II (RNAPII) nuclear targeting. Here, we investigated the effect of a cancer-associated Q279* nonsense mutation in Gpn3 cellular function. Employing RNAi, we replaced endogenous Gpn3 by wt or Q279* RNAi-resistant Gpn3R in epithelial model cells. RNAPII nuclear accumulation and transcriptional activity were markedly decreased in cells expressing only Gpn3R Q279*. Wild-type Gpn3R localized to the cytoplasm but a fraction of Gpn3R Q279* entered the cell nucleus and inhibited Gpn1-EYFP nuclear export. This property and the transcriptional deficit in Gpn3R Q279*-expressing cells required a PDZ-binding motif generated by the Q279* mutation. We conclude that an acquired PDZ-binding motif in Gpn3 Q279* caused Gpn3 nuclear entry, and inhibited Gpn1 nuclear export and Gpn3-mediated RNAPII nuclear targeting.
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