Use of label-free optical biosensors to detect modulation of potassium channels by G-protein coupled receptors

Label-Free Sensing on Microarrays

Microarrays of biological molecules such as DNAs, proteins, carbohydrates, and small molecules provide a high-throughput platform for screening tens of thousands of biomolecular interactions simultaneously, facilitating the functional characterization of these biomolecules in areas of genomics, proteomics, glycomics, and cytomics. Routinely, analysis of binding reactions between solution-phased probes and surface-immobilized targets involves some kinds of fluorescence-based detection methods. Even though these methods have advantages of high sensitivity and wide dynamic range, labeling probes and/or targets inevitably changes their innate properties and in turn affects probe-target interactions in often uncharacterized ways. Therefore, in recent years, various label-free sensing technologies have been developed for characterizing biomolecular interactions in microarray format. These biosensors, to a certain extent, take the place of fluorescent methods by providing a comparable sensitivity as well as retaining the conformational and functional integrality of biomolecules to be investigated. More importantly, some of these biosensors are capable of real-time monitoring probe-target interactions, providing the binding affinities of these reactions. Using label-free biosensors in microarrays has become a current trend in developing high-throughput screening platforms for drug discoveries and applications in all areas of "-omics." This article is aimed to provide principles and recent developments in label-free sensing technologies applicable to microarrays, with special attentions being paid to surface plasmon resonance microscopy and oblique-incidence reflectivity difference microscopy.

Stimulation of Slack K(+) Channels Alters Mass at the Plasma Membrane by Triggering Dissociation of a Phosphatase-Regulatory Complex

Human mutations in the cytoplasmic C-terminal domain of Slack sodium-activated potassium (KNa) channels result in childhood epilepsy with severe intellectual disability. Slack currents can be increased by pharmacological activators or by phosphorylation of a Slack C-terminal residue by protein kinase C. Using an optical biosensor assay, we find that Slack channel stimulation in neurons or transfected cells produces loss of mass near the plasma membrane. Slack mutants associated with intellectual disability fail to trigger any change in mass. The loss of mass results from the dissociation of the protein phosphatase 1 (PP1) targeting protein, Phactr-1, from the channel. Phactr1 dissociation is specific to wild-type Slack channels and is not observed when related potassium channels are stimulated. Our findings suggest that Slack channels are coupled to cytoplasmic signaling pathways and that dysregulation of this coupling may trigger the aberrant intellectual development associated with specific childhood epilepsies.