Mechanistic insights into staphylopine-mediated metal acquisition.

Metal acquisition is vital to pathogens for successful infection within hosts. Staphylopine (StP), a broad-spectrum metallophore biosynthesized by the major human pathogen, Staphylococcus aureus, plays a central role in transition-metal acquisition and bacterial virulence. The StP-like biosynthesis loci are present in various pathogens, and the proteins responsible for StP/metal transportation have been determined. However, the molecular mechanisms of how StP/metal complexes are recognized and transported remain unknown. We report multiple structures of the extracytoplasmic solute-binding protein CntA from the StP/metal transportation system in apo form and in complex with StP and three different metals. We elucidated a sophisticated metal-bound StP recognition mechanism and determined that StP/metal binding triggers a notable interdomain conformational change in CntA. Furthermore, CRISPR/Cas9-mediated single-base substitution mutations and biochemical analysis highlight the importance of StP/metal recognition for StP/metal acquisition. These discoveries provide critical insights into the study of novel metal-acquisition mechanisms in microbes.

Transition-Metal-Free Stereospecific Cross-Coupling with Alkenylboronic Acids as Nucleophiles.

We herein report a transition-metal-free cross-coupling between secondary alkyl halides/mesylates and aryl/alkenylboronic acid, providing expedited access to a series of nonchiral/chiral coupling products in moderate to good yields. Stereospecific SN2-type coupling is developed for the first time with alkenylboronic acids as pure nucleophiles, offering an attractive alternative to the stereospecific transition-metal-catalyzed C(sp(2))-C(sp(3)) cross-coupling.

A sulfonic-azobenzene-grafted silica amphiphilic material: a versatile stationary phase for mixed-mode chromatography.

A novel sulfonic-azobenzene-functionalized amphiphilic silica material was synthesized through the preparation of a new sulfonic azobenzene monomer and its grafting on mercaptopropyl-modified silica by a surface-initiated radical chain-transfer reaction. The synthesis was confirmed by infrared spectra, elemental analysis, and thermogravimetric analysis. This new material was successfully applied as a new kind of mixed-mode stationary phase in liquid chromatography. This allows an exceptionally flexible adjustment of retention and selectivity by tuning the experimental conditions. The distinct separation mechanisms were outlined by selected examples of chromatographic separations in the different modes. In reversed-phase liquid chromatography, this new stationary phase presented specific chromatographic performance when evaluated using a Tanaka test mixture. Seven dinitro aromatic isomers, four steroids, and seven flavonoids were separated successfully in simple reversed-phase mode. This stationary phase can also be used in hydrophilic interaction chromatography because of the existing polar functional groups; for this, nucleosides and their bases were used as a test mixture. Interestingly, the same nucleosides and bases can also be separated in per aqueous liquid chromatography using the same stationary phase. Three ginsenosides including Rg1, Re, and Rb1 were successfully separated in hydrophilic mode. There is the potential for more applications to benefit from this useful column.

CRISPR/Cas9-based Genome Editing in Pseudomonas aeruginosa and Cytidine Deaminase-Mediated Base Editing in Pseudomonas Species.

Pseudomonas species are a large class of gram-negative bacteria that exhibit significant biomedical, ecological, and industrial importance. Despite the extensive research and wide applications, genetic manipulation in Pseudomonas species, in particular in the major human pathogen Pseudomonas aeruginosa, remains a laborious endeavor. Here we report the development of a genome editing method pCasPA/pACRISPR by harnessing the CRISPR/Cas9 and the phage λ-Red recombination systems. The method allows for efficient and scarless genetic manipulation in P. aeruginosa. By engineering the fusion of the cytidine deaminase APOBEC1 and the Cas9 nickase, we further develop a base editing system pnCasPA-BEC, which enables highly efficient gene inactivation and point mutations in a variety of Pseudomonas species, such as P. aeruginosa, Pseudomonas putida, Pseudomonas fluorescens, and Pseudomonas syringae. Application of the two genome editing methods will dramatically accelerate a wide variety of investigations, such as bacterial physiology study, drug target exploration, and metabolic engineering.

Highly efficient base editing in Staphylococcus aureus using an engineered CRISPR RNA-guided cytidine deaminase.

Novel therapeutic means against Staphylococcus aureus infections are urgently needed due to the emergence of drug-resistant S. aureus. We report the development of a CRISPR RNA-guided cytidine deaminase (pnCasSA-BEC), enabling highly efficient gene inactivation and point mutations in S. aureus. We engineered a fusion of a Cas9 nickase (Cas9D10A) and a cytidine deaminase (APOBEC1) that can be guided to a target genomic locus for gene inactivation via generating a premature stop codon. The pnCasSA-BEC system nicks the non-edited strand of the genomic DNA, directly catalyzes the conversion of cytidine (C) to uridine (U), and relies on DNA replication to achieve C → T (G → A) conversion without using donor repair templates. The development of the base-editing system will dramatically accelerate drug-target exploration in S. aureus and provides critical insights into the development of base-editing tools in other microbes.

A novel green approach for the chemical modification of silica particles based on deep eutectic solvents.

Deep eutectic solvents (DESs), as a novel class of green solvents, were successfully applied as eco-friendly and sustainable reaction media for fast surface modification of spherical porous silica, resulting in stationary phases for high-performance liquid chromatography. The new reaction media were advantageous over organic solvents in many aspects, such as the high dispersibility of silica spheres and their non-volatility.

Hairpin assembly-triggered cyclic activation of a DNA machine for label-free and ultrasensitive chemiluminescence detection of DNA.

DNA plays important regulatory roles in many life activities. Here, we have developed a novel label-free, ultrasensitive and specific chemiluminescence (CL) assay protocol for DNA detection based on hairpin assembly-triggered cyclic activation of a DNA machine. The system involves two hairpin structures, H1 and H2. Firstly, a target DNA binds with and opens the hairpin structure of H1. Then, H2 hybridizes with H1 and displaces the target DNA, which is used to trigger another new hybridization cycle between H1 and H2, leading to the generation of numerous H1-H2 complexes. The generated H1-H2 complexes are further activated with the help of polymerase and nicking enzyme, continuously yielding a large amount of G-riched DNA fragments. The G-riched DNA fragment products interact with hemin to form the activated HRP-mimicking DNAzymes that can catalyze the oxidation of luminol by H2O2 to produce strong CL signal resulting in an amplified sensing process. Our newly proposed homogeneous assay enables the quantitative measurement of p53 DNA (as a model) with a detection limit of 0.85 fM, which is at least 5 orders of magnitude lower than that of traditional unamplified homogeneous optical approaches. Moreover, this assay exhibits high discrimination ability even against a single base mismatch. In addition, this strategy is also capable of detecting p53 DNA in complex biological samples. The proposed sensing approach might hold a great promise for further applications in biomedical research and early clinical diagnosis.

Novel imidazolium-embedded and imidazolium-spaced octadecyl stationary phases for reversed phase liquid chromatography.

Two new stationary phases modified by alkylimidazoliums were prepared for the first time and characterized. One of the new phases was obtained via monomeric immobilization of octadecylimidazole to γ-chloropropyltrimethoxysilane modified silica to form polar-embedded phase; the other one was prepared by co-immobilization of two silane coupling agents (γ-chloropropyltrichlorosilane and octadecyltrichlorosilane) to silica, followed by quaternization of methylimidazole to form polar-spaced phase. This study was intended to compare the retention characteristics of these two stationary phases using linear solvation energy relationships model, as well as to examine the difference in selectivity by eluting alkylbenzenes, alkylnaphthalenes, condensed-ring and phenylene polynuclear aromatic hydrocarbons on both phases. Different effects of distributions of polar functional group and octadecyl chain were found to impact the chromatographic properties.

A novel urea-functionalized surface-confined octadecylimidazolium ionic liquid silica stationary phase for reversed-phase liquid chromatography.

One-pot synthesis of surface-confined ionic liquid functionalized silica spheres was proposed using N-(3-aminopropyl)imidazole, γ-isopropyltriethoxysilane and 1-bromooctadecane as starting materials. The surface modification of the silica spheres was successful with a high surface density of octadecylimidazolium, enabling the utilization of this new urea-functionalized ionic liquid-grafted silica material as stationary phase for high-performance liquid chromatography in reversed-phase mode. The long aliphatic chain combined with the multiple polar group embedded in the ligands imparted the new stationary phase fine selectivity towards PAH isomers and polar aromatics and higher affinity for phenolic compounds. The unique features of the new material, especially the effect of the urea group on the retention were elucidated by mathematic modeling.

Deep eutectic solvents as novel extraction media for phenolic compounds from model oil.

Deep eutectic solvents (DES) as a new kind of green solvent were used for the first time to excellently extract phenolic compounds from model oil. It was also proved that DES could be used to extract other polar compounds from non-polar or weakly-polar solvents by liquid-phase microextraction.