Enzyme-linked electrochemical DNA ligation assay using magnetic beads

Biochemical and Structural Characterisation of DNA Ligases from Bacteria and Archaea

DNA ligases are enzymes that seal breaks in the backbones of DNA, leading to them being essential for the survival of all organisms. DNA ligases have been studied from many different types of cells and organisms and shown to have diverse sizes and sequences, with well conserved specific sequences that are required for enzymatic activity. A significant number of DNA ligases have been isolated or prepared in recombinant forms and, here, we review their biochemical and structural characterisation. All DNA ligases contain an essential lysine that transfers an adenylate group from a co-factor to the 5'-phosphate of the DNA end that will ultimately be joined to the 3'-hydroxyl of the neighbouring DNA strand. The essential DNA ligases in bacteria use nicotinamide adenine dinucleotide ( β -NAD+) as their co-factor whereas those that are essential in other cells use adenosine-5'-triphosphate (ATP) as their co-factor. This observation suggests that the essential bacterial enzyme could be targeted by novel antibiotics and the complex molecular structure of β -NAD+ affords multiple opportunities for chemical modification. Several recent studies have synthesised novel derivatives and their biological activity against a range of DNA ligases has been evaluated as inhibitors for drug discovery and/or non-natural substrates for biochemical applications. Here, we review the recent advances that herald new opportunities to alter the biochemical activities of these important enzymes. The recent development of modified derivatives of nucleotides highlights that the continued combination of structural, biochemical and biophysical techniques will be useful in targeting these essential cellular enzymes.

Rapid and sensitive detection of HIV-1 p24 antigen by immunomagnetic separation coupled with catalytic fluorescent immunoassay

In this study, a system of magnetic beads (MBs) coupled with catalytic fluorescent immunoassay for rapid and sensitive determination of HIV-1 capsid antigen p24 was developed. p24 was captured by antibody immobilized MBs, and the detection antibody was linked to horseradish peroxidase (HRP) through biotin-streptavidin recognition, catalyzing the oxidation of o-phenylenediamine (OPD) and hydrogen peroxide to produce a fluorescent product. This is the first reported utilization of the fluorescence of OPD oxidation product catalyzed by HRP for immunoassay. Optimization of conditions afforded a low detection limit of 0.5 pg/mL (3σ) for p24 with a linear range of 1.4-90.0 pg/mL. The assay exhibited good reproducibility with a relative standard deviation (RSD) of 4.4 %, 4.7 %, and 5.0 % for detecting 1.4 pg/mL, 22.5 pg/mL, and 45.0 pg/mL p24, respectively. The assay can be completed in less than 90 min. Moreover, the proposed method was successfully applied to detect p24 in spiked serum. This method overcomes the interference of MBs to the fluorescence signal and demonstrated higher sensitivity for detection of p24 than conventional ELISA kits. The system could be applied for detecting other antigens with high sensitivity, rapidity, specificity, and simple operation. Graphical Abstract A rapid and sensitive biosensing method coupling immunomagnetic separation and catalytic fluorescence for determination of HIV-1 p24 has been developed.

A facile and highly sensitive impedimetric DNA biosensor with ultralow background response based on in situ reduced graphene oxide

A facile and highly sensitive impedimetric DNA biosensor with ultralow background response based on in situ reduced graphene oxide.