The cytosolic Arabidopsis thaliana cysteine desulfurase ABA3 delivers sulfur to the sulfurtransferase STR18.

The biosynthesis of many sulfur-containing molecules depends on cysteine as a sulfur source. Both the cysteine desulfurase (CD) and rhodanese (Rhd) domain-containing protein families participate in the trafficking of sulfur for various metabolic pathways in bacteria and human, but their connection is not yet described in plants. The existence of natural chimeric proteins containing both CD and Rhd domains in specific bacterial genera, however, suggests a general interaction between these proteins. We report here the biochemical relationships between two cytosolic proteins from Arabidopsis thaliana, a Rhd domain-containing protein, the sulfurtransferase 18 (STR18), and a CD isoform referred to as ABA3, and compare these biochemical features to those of a natural CD-Rhd fusion protein from the bacterium Pseudorhodoferax sp. We observed that the bacterial enzyme is bifunctional exhibiting both CD and STR activities using l-cysteine and thiosulfate as sulfur donors but preferentially using l-cysteine to catalyze transpersulfidation reactions. In vitro activity assays and mass spectrometry analyses revealed that STR18 stimulates the CD activity of ABA3 by reducing the intermediate persulfide on its catalytic cysteine, thereby accelerating the overall transfer reaction. We also show that both proteins interact in planta and form an efficient sulfur relay system, whereby STR18 catalyzes transpersulfidation reactions from ABA3 to the model acceptor protein roGFP2. In conclusion, the ABA3-STR18 couple likely represents an uncharacterized pathway of sulfur trafficking in the cytosol of plant cells, independent of ABA3 function in molybdenum cofactor maturation.

Evaluating how cationic lipid affects mRNA-LNP physical properties and biodistribution.

RNA therapeutics represents a powerful strategy for diseases where other approaches have failed, especially given the recent successes of mRNA vaccines against the coronavirus disease 2019 (COVID-19) and small interfering (siRNA) therapeutics. However, further developments are still required to reduce toxicity, improve stability and biodistribution of mRNA-LNPs (lipid nanoparticles). Here, we show a rational combinatorial approach to select the best formulation based on a new cationic lipid molecule (IM21.7c), which includes an imidazolium polar head. The study allowed us to select the optimal 5 lipids composition for in vivo mRNA delivery. IM21.7c based mRNA-LNPs measuring less than 100 nm had high encapsulation efficiency, protected mRNA from degradation, and exhibited sustained release kinetics for effective in vitro transfection. Most interestingly the biodistribution was significantly different from other clinically approved LNPs, with increased targeting to the lung. Further studies are now required to expand the possible applications of these new molecules.