Abstract
The regulatory (R) subunits of the cAMP-dependent protein kinase (protein kinase A or PKA) are multi-domain proteins responsible for conferring cAMP-dependence and localizing PKA to specific subcellular locations. There are four isoforms of the R subunit in mammals that are similar in molecular mass and domain organization, but clearly serve different biological functions. Although high-resolution structures are available for the cAMP-binding domains and dimerization/docking domains of two isoforms, there are no high-resolution structures of any of the intact R subunit homodimer isoforms. The results of small-angle X-ray scattering studies presented here indicate that the RIα, RIIα, and RIIβ homodimers differ markedly in overall shape, despite extensive sequence homology and similar molecular masses. The RIIα and RIIβ homodimers have very extended, rod-like shapes, whereas the RIα homodimer likely has a compact Y-shape. Based on a comparison of the R subunit sequences, we predict that the linker regions are the likely cause of these large differences in shape among the isoforms. In addition, we show that cAMP binding does not cause large conformational changes in type Iα or IIα R subunit homodimers, suggesting that the activation of PKA by cAMP involves only local conformational changes in the R subunits.
Original language | English |
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Pages (from-to) | 1183-1194 |
Number of pages | 12 |
Journal | Journal of Molecular Biology |
Volume | 337 |
Issue number | 5 |
DOIs | |
State | Published - Apr 9 2004 |
Funding
This work was performed, in part, under the auspices of the US Department of Energy (Contract W-7405-ENG-36) and in support of the Office of Science/BER Oak Ridge Structural Molecular Biology Center. Support for this work comes from the University of California Directed Research and Development (UCDRD) CULAR grant 10005. D.V. is supported by a National Science Foundation Graduate Research Fellowship. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Basic Energy Sciences (Contract no. W-31-109-ENG-38). BioCAT is a National Institutes of Health-supported Research Center RR-008630. We thank Brian Macdonald at Los Alamos National Laboratory and the staff at the Argonne National Laboratory BioCAT beamline for their expert technical assistance in collecting the scattering data. NIH grants GM19301 and GM34921 to S.S.T. also contributed.
Keywords
- C, subunit, catalytic subunit
- D/D, dimerization/docking
- Isoform differences
- PKA, protein kinase A
- Protein kinase A
- R, subunit, regulatory subunit
- Regulatory subunit
- SAXS, small-angle X-ray scattering
- Small-angle X-ray scattering
- Structure