Resonant mirror biosensor analysis of type Iα cAMP-dependent protein kinase B domain—Cyclic nucleotide interactions

Authors

  • Wallace W. Muhonen,

    1. Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine, Grand Forks, North Dakota 58202
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  • John B. Shabb

    Corresponding author
    1. Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine, Grand Forks, North Dakota 58202
    • Department of Biochemistry and Molecular Biology, University of North Dakota School of Medicine, Grand Forks, North Dakota 58202-9037
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Abstract

A resonant mirror biosensor was used to study cyclic nucleotide-receptor interactions. In particular, a novel method was developed to determine inhibition constants (Ki) from initial rates of ligate association to immobilized ligand. This approach was applied to the comparison of cyclic nucleotide-binding properties of the wild-type isolated B domain of the cAMP-dependent protein kinase type Iα regulatory subunit and its Ala-334-Thr (A334T) variant that has altered cyclic nucleotide specificity. A cUMP-saturated form of the B domain was used for all measurements. Under the conditions used, cUMP did not affect the kinetics of B domain association to immobilized cAMP. Triton X-100 was required to stabilize the protein at nanomolar concentrations. The association and dissociation rate constants for wild-type and A334T B domains yielded equilibrium dissociation constants of 11 and 16 nM. Heterogeneity of ligate and immobilized ligand, mass transport effects, and other factors were evaluated for their influence on biosensor-determined kinetic constants. Biosensor-determined relative inhibition constants (K'i = KicAMP/K'ianalog) for 16 cyclic nucleotide analogs correlated well with those determined by a [3H]cAMP binding assay. Previously published K'i values for the B domain in the intact regulatory subunit were similar to those of the isolated B domain. The K'i values for the wild-type and A334T B domains were essentially unchanged except for dramatic enhancements in affinity of cGMP analogs for the A334T B domain. These observations validate the isolated B domain as a simple model system for studying cyclic nucleotide-receptor interactions.

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