13 research outputs found
Using Nonequilibrium Capillary Electrophoresis of Equilibrium Mixtures (NECEEM) for Simultaneous Determination of Concentration and Equilibrium Constant
Nonequilibrium capillary electrophoresis
of equilibrium mixtures
(NECEEM) is a versatile tool for studying affinity binding. Here we
describe a NECEEM-based approach for simultaneous determination of
both the equilibrium constant, <i>K</i><sub>d</sub>, and
the unknown concentration of a binder that we call a target, T. In
essence, NECEEM is used to measure the unbound equilibrium fraction, <i>R</i>, for the binder with a known concentration that we call
a ligand, L. The first set of experiments is performed at varying
concentrations of T, prepared by serial dilution of the stock solution,
but at a constant concentration of L, which is as low as its reliable
quantitation allows. The value of <i>R</i> is plotted as
a function of the dilution coefficient, and dilution corresponding
to <i>R</i> = 0.5 is determined. This dilution of T is used
in the second set of experiments in which the concentration of T is
fixed but the concentration of L is varied. The experimental dependence
of <i>R</i> on the concentration of L is fitted with a function
describing their theoretical dependence. Both <i>K</i><sub>d</sub> and the concentration of T are used as fitting parameters,
and their sought values are determined as the ones that generate the
best fit. We have fully validated this approach <i>in silico</i> by using computer-simulated NECEEM electropherograms and then applied
it to experimental determination of the unknown concentration of MutS
protein and <i>K</i><sub>d</sub> of its interactions with
a DNA aptamer. The general approach described here is applicable not
only to NECEEM but also to any other method that can determine a fraction
of unbound molecules at equilibrium
Improvements to Direct Quantitative Analysis of Multiple MicroRNAs Facilitating Faster Analysis
Studies suggest that patterns of
deregulation in sets of microRNA
(miRNA) can be used as cancer diagnostic and prognostic biomarkers.
Establishing a âmiRNA fingerprintâ-based diagnostic
technique requires a suitable miRNA quantitation method. The appropriate
method must be direct, sensitive, capable of simultaneous analysis
of multiple miRNAs, rapid, and robust. Direct quantitative analysis
of multiple microRNAs (DQAMmiR) is a recently introduced capillary
electrophoresis-based hybridization assay that satisfies most of these
criteria. Previous implementations of the method suffered, however,
from slow analysis time and required lengthy and stringent purification
of hybridization probes. Here, we introduce a set of critical improvements
to DQAMmiR that address these technical limitations. First, we have
devised an efficient purification procedure that achieves the required
purity of the hybridization probe in a fast and simple fashion. Second,
we have optimized the concentrations of the DNA probe to decrease
the hybridization time to 10 min. Lastly, we have demonstrated that
the increased probe concentrations and decreased incubation time removed
the need for masking DNA, further simplifying the method and increasing
its robustness. The presented improvements bring DQAMmiR closer to
use in a clinical setting
Surface-grafted polysarcosine as a peptoid antifouling polymer brush
Poly(N-substituted glycine) "peptoids" are a class of peptidomimetic molecules receiving significant interest as engineered biomolecules. Sarcosine (i.e., poly(N-methyl glycine)) has the simplest side chain chemical structure of this family. In this Article, we demonstrate that surface-grafted polysarcosine (PSAR) brushes exhibit excellent resistance to nonspecific protein adsorption and cell attachment. Polysarcosine was coupled to a mussel adhesive protein-inspired DOPA-Lys pentapeptide, which enabled solution grafting and control of the surface chain density of the PSAR brushes. Protein adsorption was found to decrease monotonically with increasing grafted chain densities, and protein adsorption could be completely inhibited above certain critical chain densities specific to different polysarcosine chain lengths. The dependence of protein adsorption on chain length and density was also investigated by a molecular theory. PSAR brushes at high chain length and density were shown to resist fibroblast cell attachment over a 7 week period, as well as resist the attachment of some clinically relevant bacterial strains. The excellent antifouling performance of PSAR may be related to the highly hydrophilic character of polysarcosine, which was evident from high-pressure liquid chromatography measurements of polysarcosine and water contact angle measurements of the PSAR brushes. Peptoids have been shown to resist proteolytic degradation, and polysarcosine could be produced in large quantities by N-carboxy anhydride polymerization. In summary, surface-grafted polysarcosine peptoid brushes hold great promise for antifouling applications