Stochastic sensing is an emerging approach for the detection of a wide variety of analytes at the level of individual molecules. Detection is accomplished by observing the modulation of the current that flows through a single protein pore that has been engineered to bind an analyte of interest. Previously, protein analytes have been detected by using pores to which ligands have been appended at specific sites by targeted chemical modification. Here, we report the first genetically encoded stochastic sensor element for detecting a protein. A protein kinase inhibitor peptide sequence was incorporated into the alpha-hemolysin polypeptide, which was used to form a heteroheptameric pore containing a single copy of the inhibitor sequence. With this pore, the successful detection of the catalytic subunit of protein kinase A was demonstrated. This development should greatly facilitate the detection of active kinase subunits by stochastic sensing and the rapid screening of kinase inhibitors by an approach that yields kinetic information.
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