Abstract
An aberrant fusion of the DNAJB1 and PRKACA genes generates a chimeric protein kinase (PKA-CDNAJB1) in which the J-domain of the heat shock protein 40 is fused to the catalytic α subunit of cAMP-dependent protein kinase A (PKA-C). Deceivingly, this chimeric construct appears to be fully functional, as it phosphorylates canonical substrates, forms holoenzymes, responds to cAMP activation, and recognizes the endogenous inhibitor PKI. Nonetheless, PKA-CDNAJB1 has been recognized as the primary driver of fibrolamellar hepatocellular carcinoma and is implicated in other neoplasms for which the molecular mechanisms remain elusive. Here we determined the chimera’s allosteric response to nucleotide and pseudo-substrate binding. We found that the fusion of the dynamic J-domain to PKA-C disrupts the internal allosteric network, causing dramatic attenuation of the nucleotide/PKI binding cooperativity. Our findings suggest that the reduced allosteric cooperativity exhibited by PKA-CDNAJB1 alters specific recognitions and interactions between substrates and regulatory partners contributing to dysregulation.
Highlights
An aberrant fusion of the DNAJB1 and PRKACA genes generates a chimeric protein kinase (PKA-CDNAJB1) in which the J-domain of the heat shock protein 40 is fused to the catalytic α subunit of cAMP-dependent protein kinase A (PKA-C)
Our computational and solution NMR studies suggest that PKA-CDNAJB1 spans a large ensemble of conformations, with the
We compared the small-angle X-ray scattering (SAXS) profiles of PKA-CWT and PKA-CDNAJB1. For both binary (ATPγN-bound) and ternary (ATPγN/PKI-bound) complexes of PKA-CDNAJB1, we fit the SAXS profiles with the compact (J-domain in), intermediate, and extended (J-domain out) conformations extracted from the trajectories of molecular dynamics (MD) simulations (Fig. 1b, c)
Summary
An aberrant fusion of the DNAJB1 and PRKACA genes generates a chimeric protein kinase (PKA-CDNAJB1) in which the J-domain of the heat shock protein 40 is fused to the catalytic α subunit of cAMP-dependent protein kinase A (PKA-C). This chimeric construct appears to be fully functional, as it phosphorylates canonical substrates, forms holoenzymes, responds to cAMP activation, and recognizes the endogenous inhibitor PKI. The fusion of the J-domain does not alter the structure of the catalytic core of PKA-CDNAJB1, which remains virtually identical to the wild-type kinase (PKA-CWT). PKA-CDNAJB1 binds the endogenous inhibitor PKI (both full-length and derived peptides) with an affinity comparable to wild-type[15]
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