title: The conformationally dynamic C helix of the RIalpha subunit of protein kinase A mediates isoform-specific domain reorganization upon C subunit binding.
abstract: Different isoforms of the full-length protein kinase A (PKA) regulatory subunit homodimer (R2) and the catalytic (C) subunit-bound holoenzyme (R2C2) have very different global structures despite similar molecular weights and domain organization within their primary sequences. To date, it has been the linker sequence between the R subunit dimerization/docking domain and cAMP-binding domain A that has been implicated in modulating domain interactions to give rise to these differences in global structure. The small angle solution scattering data presented here for three different isoforms of PKA heterodimer (deltaR-C) complexes reveal a role for another conformationally dynamic sequence in modulating inter-subunit and domain interactions, the C helix that connects the cAMP-binding domains A and B of the R subunit. The deltaR-C heterodimer complexes studied here were each formed with a monomeric N-terminal deletion mutant of the R subunit (deltaR) that contains the inhibitor sequence and both cAMP-binding domains. The scattering data show that type IIalpha and type IIbeta deltaR-C heterodimers are relatively compact and globular, with the C subunit contacting the inhibitor sequence and both cAMP-binding domains. In contrast, the type Ialpha heterodimer is significantly more extended, with the C subunit interacting with the inhibitor sequence and cAMP-binding domain A, whereas domain B extends out such that its surface is almost completely solvent exposed. These data implicate the C helix of RIalpha in modulating isoform-specific interdomain communication in the PKA holoenzyme, adding another layer of structural complexity to our understanding of signaling dynamics in this multisubunit, multidomain protein kinase.
authors.affiliation: Department of Chemistry and Biochemistry and Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92037, USA.
authors.forename: Dominico
authors.initials: D
authors.lastname: Vigil
authors.forename: Donald K
authors.initials: DK
authors.lastname: Blumenthal
authors.forename: Susan S
authors.initials: SS
authors.lastname: Taylor
authors.forename: Jill
authors.initials: J
authors.lastname: Trewhella
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D002417:Cattle; D000242:Cyclic AMP / Q000378:metabolism; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry*; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism; D017353:Gene Deletion; D008958:Models, Molecular; D015233:Models, Statistical; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D012542:Scattering, Radiation; D014965:X-Rays
chemical_list: D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; C517836:Prkar1a protein, rat; D020033:Protein Isoforms; D011994:Recombinant Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium