Expression and mutagenesis of the regulatory subunit of cAMP-dependent protein kinase in Escherichia coli

Methods in Enzymology (Impact Factor: 2.09). 02/1988; 159:325-36.
Source: PubMed
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    • "These mutants contained most of the linker residues compared to the previous structure of RIα (91-244). All mutants were expressed in E. coli BL21 (DE3) cells (Novagen) and purified as described previously (Saraswat et al., 1988) with slight modification. The cells were lysed and the spin supernatant was filtered with 0.22mm filter and loaded onto a Profinia protein purification system. "
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    ABSTRACT: PKA holoenzymes containing two catalytic (C) subunits and a regulatory (R) subunit dimer are activated cooperatively by cAMP. While cooperativity involves the two tandem cAMP binding domains in each R-subunit, additional cooperativity is associated with the tetramer. Of critical importance is the flexible linker in R that contains an inhibitor site (IS). While the IS becomes ordered in the R:C heterodimer, the overall conformation of the tetramer is mediated largely by the N-Linker that connects the D/D domain to the IS. To understand how the N-Linker contributes to assembly of tetrameric holoenzymes, we engineered a monomeric RIα that contains most of the N-Linker, RIα(73-244), and crystallized a holoenzyme complex. Part of the N-linker is now ordered by interactions with a symmetry-related dimer. This complex of two symmetry-related dimers forms a tetramer that reveals novel mechanisms for allosteric regulation and has many features associated with full-length holoenzyme. A model of the tetrameric holoenzyme, based on this structure, is consistent with previous small angle X-ray and neutron scattering data, and is validated with new SAXS data and with an RIα mutation localized to a novel interface unique to the tetramer.
    Full-text · Article · Feb 2011 · Structure
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    ABSTRACT: The catalytic (C) subunit of cAMP-dependent protein kinase is inhibited by the regulatory (R) subunit and by a thermostable inhibitor (PKI). Both inhibitors also affect the intracellular distribution of the C subunit. Whether injected into the cytoplasm or into the nucleus, free C subunit can enter and exit the nucleus freely. After 30 min its distribution is identical and is independent of the initial site of injection. In contrast, when C is injected into the cytoplasm complexed with R or PKI, the complexes are restricted to the cytoplasm (1-3). However, unlike the R subunit, which is restricted to the cytoplasm like the holoenzyme, free PKI enters the nucleus rapidly following its injection into the cytoplasm. When holoenzyme is injected directly into the nucleus, it cannot exit and return to the cytoplasm. In contrast, nuclear injection of a C.PKI complex results in the rapid exit of the C subunit from the nucleus. In equilibrated cells previously injected with the C subunit, subsequent cytoplasmic injection of either PKI or type 1 R depletes the nucleus of C although PKI does so faster, consistent with its ability to enter the nucleus. Both inhibitors block the cAMP response element-regulated gene expression. Hence PKI may serve as a nuclear scavenger of C providing a mechanism not only for inhibition but also for subcellular localization in the presence of cAMP by restricting the access of the C subunit to the nucleus.
    No preview · Article · Feb 1994 · Journal of Biological Chemistry
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    ABSTRACT: (RP)-cAMPS is known to inhibit competitively the cAMP-induced activation of cAMP-dependent protein kinase (PKA). The molecular nature of this inhibition, however, is unknown. By monitoring the intrinsic tryptophan fluorescence of recombinant type I regulatory subunit of PKA under unfolding conditions, a free energy value (delta GDH2O) of 8.23 +/- 0.22 kcal/mol was calculated. The cAMP-free form of the regulatory subunit was less stable with delta GDH2O = 6.04 +/- 0.05 kcal/mol. Native stability was recovered by treatment of the cAMP-free protein with either cAMP or (SP)-cAMPS but not with (RP)-cAMPS. Thus, (RP)-cAMPS binding to the regulatory subunit keeps the protein in a locked conformation, unable to release the catalytic subunit. This finding was further supported by demonstrating that holoenzyme formation was greatly accelerated only when bound cAMP was replaced with (RP)-cAMPS but not with cAMP or (SP)-cAMPS.
    Preview · Article · Dec 1995 · FEBS Letters
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