No abstract

We report on the development of a new class of kinase microarrays based on the coimmobilization of both kinase and substrate components within a single pin-printed sol-gel microarray element and the use of such arrays for nanovolume inhibition assays. We successfully immobilized the alpha-catalytic subunit of cAMP-dependent protein kinase (PKA) and the peptide substrate kemptide within sol-gel-derived microarrays for the purpose of monitoring phosphorylation and inhibition. Using Pro-Q Diamond stain as an end-point indicator of phosphorylation, we demonstrate the selective detection of phosphoproteins over nonphosphorylated controls and the ability to detect phosphorylated proteins over a 500-fold concentration range. Limits of detection for the phosphoprotein beta-casein were 7.5 pg, and the detectable signal remained linear up to 3.75 ng of protein per array spot. PKA is demonstrated to be active when coentrapped with two different substrates, and inhibition assays for PKA with the inhibitors H7 and H89 demonstrate the ability to detect kinase inhibition as well as derive IC50 plots from a single array using an overprinting method to deliver approximately 0.6 nL of reagent per array element, or a total of 72 nL of reagents to generate a full, 12-point IC50 curve in pentuplicate.

A method is described for identifying bioactive compounds in complex mixtures based on the use of capillary-scale monolithic enzyme-reactor columns for rapid screening of enzyme activity. A two-channel nanoLC system was used to continuously infuse substrate coupled with automated injections of substrate/small molecule mixtures, optionally containing the chromogenic Ellman reagent, through sol-gel derived acetylcholinesterase (AChE) doped monolithic columns. This is the first report of AChE encapsulated in monolithic silica for use as an immobilized enzyme reactor (IMER), and the first use of such IMERs for mixture screening. AChE IMER columns were optimized to allow rapid functional screening of compound mixtures based on changes in the product absorbance or the ratio of mass spectrometric peaks for product and substrate ions in the eluent. The assay had robust performance and produced a Z' factor of 0.77 in the presence of 2% (v/v) DMSO. A series of 52 mixtures consisting of 1040 compounds from the Canadian Compound Collection of bioactives was screened and two known inhibitors, physostigmine and 9-aminoacridine, were identified from active mixtures by manual deconvolution. The activity of the compounds was confirmed using the enzyme reactor format, which allowed determination of both IC(50) and K(I) values. Screening results were found to correlate well with a recently published fluorescence-based microarray screening assay for AChE inhibitors.