A Ca(2+)-dependent global conformational change in the 3D structure of phosphorylase kinase obtained from electron microscopy.
Phosphorylase kinase (PhK), a Ca(2+)-dependent regulatory enzyme of the glycogenolytic cascade in skeletal muscle, is a 1.3 MDa hexadecameric oligomer comprising four copies of four distinct subunits, termed alpha, beta, gamma, and delta, the last being endogenous calmodulin. The structures of both nonactivated and Ca(2+)-activated PhK were determined to elucidate Ca(2+)-induced structural changes associated with PhK's activation. Reconstructions of both conformers of the kinase, each including over 11,000 particles, yielded bridged, bilobal structures with resolutions estimated by Fourier shell correlation at 24 A using a 0.5 correlation cutoff, or at 18 A by the 3sigma (corrected for D(2) symmetry) threshold curve. Extensive Ca(2+)-induced structural changes were observed in regions encompassing both the lobes and bridges, consistent with changes in subunit interactions upon activation. The relative placement of the alpha, beta, gamma, and delta subunits in the nonactivated three-dimensional structure, relying upon previous two-dimensional localizations, is in agreement with the known effects of Ca(2+) on subunit conformations and interactions in the PhK complex.
Nadeau
Owen W
OW
Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, USA.
Carlson
Gerald M
GM
Gogol
Edward P
EP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron / Q000379:methods; D008958:Models, Molecular; D010764:Phosphorylase Kinase / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D011817:Rabbits
D021122:Protein Subunits; D010764:Phosphorylase Kinase; D002118:Calcium