Effect of pressure on antigen-antibody complexes: modulation by temperature and ionic strength

Sink/Float Magnetic Immunoassays for In-Field Bioassays

Analytical tests/devices that are used outside laboratory settings are required to have a very simple analytical protocol to get clearance by regulatory authorities. This study describes sink/float magnetic immunoassays, a new type of rapid, mix-and-observe, instrument-free tests for the detection of biomarkers in untreated biological samples that are very simple and might meet the simple-to-use criterion of authorities to be used in the field. These tests can tell whether an analyte is above or below a predetermined level within 25-45 minutes based on the sinking or floating of a mm-sized sphere on the surface of which an immunoassay that uses reporter antibodies conjugated to superparamagnetic nanoparticles is performed. This manuscript describes the theory and proof-of-concept applications of sink/float magnetic immunoassays for the detection of C-Reactive Protein, anti-Treponema pallidum antibodies and E. coli bacteria.

A molecular tuning fork in single-molecule mechanochemical sensing

The separate arrangement of target recognition and signal transduction in conventional biosensors often compromises the real-time response and can introduce additional noise. To address these issues, we combined analyte recognition and signal reporting by mechanochemical coupling in a single-molecule DNA template. We incorporated a DNA hairpin as a mechanophore in the template, which, under a specific force, undergoes stochastic transitions between folded and unfolded hairpin structures (mechanoescence). Reminiscent of a tuning fork that vibrates at a fixed frequency, the device was classified as a molecular tuning fork (MTF). By monitoring the lifetime of the folded and unfolded hairpins with equal populations, we were able to differentiate between the mono- and bivalent binding modes during individual antibody-antigen binding events. We anticipate these mechanospectroscopic concepts and methods will be instrumental for the development of novel bioanalyses.

Characterization and optimization of a red-shifted fluorescence polarization ADP detection assay

ATP depletion and ADP formation are generic detection methods used for the identification of kinase and other ATP-utilizing enzyme inhibitors in high-throughput screening campaigns. However, the most widely used nucleotide detection approaches require high ATP consumption rates or involve the use of coupling enzymes, which can complicate the selection of lead compounds. As an alternative, we have developed the Transcreener (BellBrook Labs, Madison, WI) platform, which relies on the direct immunodetection of nucleotides. Here we describe the development of antibodies with >100-fold selectivity for ADP versus ATP, which enable robust detection of initial velocity rates (Z' > 0.7 at 10% substrate consumption) at ATP concentrations ranging from 0.1 microM to 1,000 microM in a competitive fluorescence polarization (FP) immunoassay. Competitive binding experiments indicate similar affinities for other nucleotide diphosphates, including 2' -deoxy ADP, GDP, and UDP. The antibody-tracer complex and the red-shifted, ratiometric FP signal are stable for at least 24 h at room temperature, providing suitable conditions for high-throughput screening. A method for calculating a kinase ATP Km with this FP immunoassay is also presented. The Transcreener ADP assay provides a simple, generic assay platform for inhibitor screening and selectivity profiling that can be used for any ADP-generating enzyme.

Influence of pressure on the chromatographic behavior of insulin variants under nonlinear conditions

The effect of pressure on the chromatographic behavior of two insulin variants in RPLC was investigated on a YMC-ODS C18 column, under nonlinear conditions. The adsorption isotherm data of porcine insulin and Lispro were measured at average column pressures ranging from 52 to 242 bar. These data fit well to the Toth and the bi-Langmuir isotherm models. The saturation capacity increases rapidly with increasing pressure while the affinity (or equilibrium) constant and the parameter characterizing the surface heterogeneity decrease. It is noteworthy that the distribution coefficient of the insulin variants increases with increasing pressure whereas their equilibrium constant b decreases for porcine insulin and increases for Lispro. The association constant b(ds), which characterizes the adsorption and desorption equilibrium of insulin in the system, increases with increasing pressure. The excellent agreement between the experimental overloaded profiles recorded under different pressures and those calculated using the POR model suggests that the chromatographic behavior of insulin is controlled more by equilibrium thermodynamics than by the mass transfer kinetics. The latter seems to be nearly independent of the average column pressure. Thus, increasing the average column pressure is an efficient, albeit costly, way to increase the loading capacity of the column, hence the production rate in preparative chromatography.

The use of high pressure for separation and production of bioactive molecules

Due to its action on the forces governing inter- and intramolecular interactions, the application of high pressure to biopurification or bio-elaboration of a product are of interest. The two closely thermodynamically related parameters, pressure and temperature, render processes based on their action clean, as no chemical reagents have to be added (and thus further removed) when they are applied. The use of high pressure in the development of desorption methods for the purification of bioactive molecules, particularly in the immunoaffinity field, is reviewed and discussed. Also mentioned is the application of the pressure parameter during the synthesis of a bioreagent. Finally, integrated processes relative to the synthesis and purification of these compounds are proposed.

Aromatic residues mediate the pressure-induced association of digoxigenin and antibody 26-10

We have previously found that the complex between fluorescently labeled digoxigenin and the monoclonal antibody 26-10 forms with a decrease in volume of approximately 30 ml/mol, leading to increased association of these species under applied hydrostatic pressure. In the present study, we have utilized a panel of mutant antibodies and Fab fragments, previously characterized for their importance in the binding affinity of digoxin:26-10, to probe the molecular basis of pressure sensitivity in this complex, as measured by fluorescence polarization spectroscopy. Several mutations that result in marked decreases in affinity exerted little or no significant effect on the association volume. Mutation at any of several key aromatic residues of the 26-10 Fab heavy chain led to a decrease in the pressure-induced association, and two mutants with Trp-->Arg mutations at heavy chain residue 100 exhibited pressure-induced dissociation. The effect of charged groups was found to depend on their proximity to contacting aromatic groups. The ability to understand and control the pressure sensitivity of antigen-antibody complexes has numerous potential applications in immunoseparations and immunosensors.