Entrapment of Src Protein Tyrosine Kinase in Sugar-Modified Silica
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A novel sugar-modified silica has been used to entrap for the first time a protein tyrosine kinase (PTK). Silane precursors bearing covalently attached gluconamide moieties were used in combination with the biocompatible precursor diglycerylsilane (DGS) to generate sol-gel derived silica that was able to encapsulate highly active Src PTK and preserve the activity of the enzyme over multiple uses. The relative activity of the enzyme was assayed using a LANCE based fluorescence resonance energy transfer method involving time-gated detection of fluorescence from a europium labeled antiphosphotyrosine antibody and Cy5 labeled streptavidin upon mutual binding to biotinylated phosphopeptides. Using this detection method, with the antibody and streptavidin external to the sol-gel matrix, it was possible to detect the phosphorylation of peptides with molecular weights of up to 2300 Da using the entrapped enzyme in N-(3-triethoxysilylpropyl)gluconamide (GLTES) doped glasses. Src kinase-doped glasses, derived from precursors such as tetramethyl orthosilicate, tetraethyl orthosilicate, or DGS that did not contain GLTES, provided no detectable enzyme activity. The addition of 1 mM ATP to the GLTES/DGS sol before the encapsulation of the protein increased the activity of the enzyme in the resulting gel, likely through a ligand-based stabilization mechanism. The use of such a system for determination of PTK activity and inhibition is demonstrated, setting the stage for the development of chromatographic and microarray based methods for the screening of kinase inhibitors.
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