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PKA Type IIa Holoenzyme Structure Reveals Isoform Diversity for Inhibition of Catalysis
Author(s) -
Wu Jian,
Brown Simon HJ,
Daake Sventja,
Taylor Susan S
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.1011.3
Subject(s) - gene isoform , protein subunit , helix (gastropod) , chemistry , binding site , stereochemistry , biophysics , mutant , protein structure , biochemistry , biology , gene , ecology , snail
Isoform diversity of the regulatory (R) subunits, RI and RII, of cAMP‐dependent protein kinase (PKA) is a primary mechanism for achieving specificity. The RII subunits are substrates as well as inhibitors and do not require ATP to form holoenzyme, which distinguishes them from RI subunits. To understand isoform diversity, we solved the crystal structure of an RIIα holoenzyme complex. The deletion mutant, RIIα (90–400), contains the unphosphorylated inhibitor site and two cAMP‐binding domains (CNB‐A and CNB‐B). The inhibitor site with a P‐site Ser docks to the large lobe but does not engage the small lobe or the C‐terminal tail. The C‐subunit is in an open conformation. The CNB‐A domain, which dominates the interface, extends from the αG helix to the Activation Loop. The CNB‐B domain, which is essential for high affinity binding of RII, but not RI‐subunit, docks to a novel AGC‐specific insert in the αH‐αI loop. The helical subdomains of RIIα undergo major conformational changes upon binding to C. The hallmark of this conformational reorganization is that the two CNB domains are splayed apart by the fusion of the αB/αC helix in CNB‐A while the αC helix of CNB‐B assumes a helix‐turn‐helix motif. Many of the multivalent contacts between C and R are made by residues that were solvent exposed in the cAMP‐bound conformation. This structure also provides a new paradigm for designing isoform‐specific activators or antagonists for PKA.