Block Copolymer Micellization of DNA Origami Promotes Solubility in Organic Solvents.

The DNA origami technique allows the precise synthesis of complex, biocompatible nanomaterials containing small molecules, biomolecules, and inorganic nanoparticles. The negatively charged phosphates in the backbone make DNA highly water-soluble and require salts to shield its electrostatic repulsion. DNA origamis are therefore not soluble in most organic solvents. While this is not problematic for applications in biochemistry, biophysics, or nanomedicine, other potential applications, processes, and substrates are incompatible with saline solutions, which include the synthesis of many nanomaterials, and reactions in templated synthesis, the operation of nanoelectronic devices, or semiconductor fabrication. To overcome this limitation, we coated DNA origami with amphiphilic poly(ethylene glycol) polylysine block copolymers and transferred them into various organic solvents including chloroform, dichloromethane, acetone, or 1-propanol. Our approach maintains the shape of the nanostructures and protects functional elements bound to the structure, such as fluorophores, gold nanoparticles, or proteins. The DNA origami polyplex micellization (DOPM) strategy hence enables solubilization or a phase transfer of complex structures into various organic solvents, which significantly expands the use of DNA origami for a range of potential applications and technical processes.

Screening for Microbial Metal-Chelating Siderophores for the Removal of Metal Ions from Solutions.

To guarantee the supply of critical elements in the future, the development of new technologies is essential. Siderophores have high potential in the recovery and recycling of valuable metals due to their metal-chelating properties. Using the Chrome azurol S assay, 75 bacterial strains were screened to obtain a high-yield siderophore with the ability to complex valuable critical metal ions. The siderophore production of the four selected strains Nocardioides simplex 3E, Pseudomonas chlororaphis DSM 50083, Variovorax paradoxus EPS, and Rhodococcus erythropolis B7g was optimized, resulting in significantly increased siderophore production of N. simplex and R. erythropolis. Produced siderophore amounts and velocities were highly dependent on the carbon source. The genomes of N. simplex and P. chlororaphis were sequenced. Bioinformatical analyses revealed the occurrence of an achromobactin and a pyoverdine gene cluster in P. chlororaphis, a heterobactin and a requichelin gene cluster in R. erythropolis, and a desferrioxamine gene cluster in N. simplex. Finally, the results of the previous metal-binding screening were validated by a proof-of-concept development for the recovery of metal ions from aqueous solutions utilizing C18 columns functionalized with siderophores. We demonstrated the recovery of the critical metal ions V(III), Ga(III), and In(III) from mixed metal solutions with immobilized siderophores of N. simplex and R. erythropolis.

VpStyA1/VpStyA2B of Variovorax paradoxus EPS: An Aryl Alkyl Sulfoxidase Rather than a Styrene Epoxidizing Monooxygenase.

Herein we describe the first representative of an E2-type two-component styrene monooxygenase of proteobacteria. It comprises a single epoxidase protein (VpStyA1) and a two domain protein (VpStyA2B) harboring an epoxidase (A2) and a FAD-reductase (B) domain. It was annotated as VpStyA1/VpStyA2B of Variovorax paradoxus EPS. VpStyA2B serves mainly as NADH:FAD-oxidoreductase. A Km of 33.6 ± 4.0 µM for FAD and a kcat of 22.3 ± 1.1 s-1 were determined and resulted in a catalytic efficiency (kcatKm-1) of 0.64 s-1 µM-1. To investigate its NADH:FAD-oxidoreductase function the linker between A2- and B-domain (AREAV) was mutated. One mutant (AAAAA) showed 18.7-fold higher affinity for FAD (kcatKm-1 of 5.21 s-1 µM-1) while keeping wildtype NADH-affinity and -oxidation activity. Both components, VpStyA2B and VpStyA1, showed monooxygenase activity on styrene of 0.14 U mg-1 and 0.46 U mg-1, as well as on benzyl methyl sulfide of 1.62 U mg-1 and 3.11 U mg-1, respectively. The high sulfoxidase activity was the reason to test several thioanisole-like substrates in biotransformations. VpStyA1 showed high substrate conversions (up to 95% in 2 h) and produced dominantly (S)-enantiomeric sulfoxides of all tested substrates. The AAAAA-mutant showed a 1.6-fold increased monooxygenase activity. In comparison, the GQWCSQY-mutant did neither show monooxygenase nor efficient FAD-reductase activity. Hence, the linker between the two domains of VpStyA2B has effects on the reductase as well as on the monooxygenase performance. Overall, this monooxygenase represents a promising candidate for biocatalyst development and studying natural fusion proteins.