title: Mass Spectrometric Analysis of Surface-Exposed Regions in the Hexadecameric Phosphorylase Kinase Complex.
abstract: Phosphorylase kinase (PhK) is a 1.3 MDa (αβγδ)4 enzyme complex, in which αβγδ protomers associate in D2 symmetry to form two large octameric lobes that are interconnected by four bridges. The approximate locations of the subunits have been mapped in low-resolution cryo-electron microscopy structures of the complex; however, the disposition of the subunits within the complex remains largely unknown. We have used partial proteolysis and chemical footprinting in combination with high-resolution mass spectrometry to identify surface-exposed regions of the intact nonactivated and phospho-activated conformers. In addition to the known interaction of the γ subunit's C-terminal regulatory domain with the δ subunit (calmodulin), our exposure results indicate that the catalytic core of γ may also anchor to the PhK complex at the bottom backside of its C-terminal lobe facing away from the active site cleft. Exposed loops on the α and β regulatory subunits within the complex occur at regions overlapping with tissue-specific alternative RNA splice sites and regulatory phosphorylatable domains. Their phosphorylation alters the surface exposure of α and β, corroborating previous biophysical and biochemical studies that detected phosphorylation-dependent conformational changes in these subunits; however, for the first time, specific affected regions have been identified.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States.
authors.forename: Mary Ashley
authors.initials: MA
authors.lastname: Rimmer
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States.
authors.forename: Antonio
authors.initials: A
authors.lastname: Artigues
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States.
authors.forename: Owen W
authors.initials: OW
authors.lastname: Nadeau
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States.
authors.forename: Maria T
authors.initials: MT
authors.lastname: Villar
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States.
authors.forename: Victor
authors.initials: V
authors.lastname: Vasquez-Montes
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Kansas Medical Center , Kansas City, Kansas 66160, United States.
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Carlson
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D013058:Mass Spectrometry; D008958:Models, Molecular; D010449:Peptide Mapping; D010764:Phosphorylase Kinase / Q000737:chemistry* / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D059748:Proteolysis; D011817:Rabbits
chemical_list: D021122:Protein Subunits; D010764:Phosphorylase Kinase