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A structural analysis of the regulatory domain from the cGMP-dependent protein kinase Iα

Background

The cGMP-dependent protein kinase (PKG) has two tandem cyclic nucleotide binding (CNB) domains which act as the primary intracellular receptor for cGMP [1, 2]. PKG exhibits a homodimeric rod-like structure which undergoes significant molecular rearrangements upon the binding of cGMP [35]. However, a detailed structural analysis of the core regulatory elements inherent to PKG is still required.

Results

We recently solved a crystal structure of the two cGMP binding sites from PKG Iα in order to highlight the atomic details of the regulatory domain. This PKG78-355 structure is free of cGMP and presents the protein in an elongated conformation. A surprising dimeric arrangement between PKG78-355 protomers is orchestrated via hydrophobic contacts between a novel helical element C-terminal to the second cGMP binding site (the switch helix) and the opposite CNB domain B (Figure 1). Small angle X-ray scattering (SAXS) of PKG78-355 suggests an overall molecular dimension of ~130 Å, consistent with the maximal linear dimension observed in our crystal structure. Upon incubation with cGMP, PKG78-355 contracted to ~95 Å. This molecular compaction was not observed in a construct lacking the switch helix (PKG78-326), suggesting the additional importance of the switch helix in mediating cGMP-specific conformational changes inherent to the regulatory domain.

Figure 1
figure1

Overall fold of PKG78-355. The crystal structure of the PKG regulatory domain identifies a novel allosteric interface between PKG78-355 protomers.

Conclusion

Overall, these studies provide the first atomic resolution model of tandem cGMP binding domains and expand our understanding of the allosteric mechanisms surrounding PKG activation.

References

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Author information

Correspondence to Brent W Osborne.

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This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Keywords

  • Regulatory Domain
  • Hydrophobic Contact
  • Atomic Detail
  • Detailed Structural Analysis
  • Allosteric Mechanism