title: Cryo-EM imaging of the catalytic subunit of the DNA-dependent protein kinase.
abstract: The DNA-dependent protein kinase (DNA-PK) plays an important role in mammalian DNA double-strand break repair and immunoglobulin gene rearrangement. The DNA-PK holoenzyme is activated by assembly at DNA ends and is comprised of DNA-PKcs, a 460 kDa protein kinase catalytic subunit, and Ku, a 70 kDa/80 kDa heterodimeric DNA-targeting component. We have solved the three-dimensional structure of DNA-PKcs to approximately 21 A resolution by analytically combining images of nearly 9500 individual particles extracted from cryo-electron micrographs. The DNA-PKcs protein has an open, pseudo 2-fold symmetric structure with a gap separating a crown-shaped top from a rounded base. Columns of density are observed to protrude into the gap from both the crown and the base. Measurements of the enclosed volume indicate that the interior of the protein is largely hollow. The structure of DNA-PKcs suggests that its association with DNA may involve the internalization of double-stranded ends.
authors.affiliation: Department of Molecular and Medical Pharmacology, Crump Institute for Biological Imaging, UCLA School of Medicine, Los Angeles, CA 90095, USA.
authors.forename: C Y
authors.initials: CY
authors.lastname: Chiu
authors.forename: R B
authors.initials: RB
authors.lastname: Cary
authors.forename: D J
authors.initials: DJ
authors.lastname: Chen
authors.forename: S R
authors.initials: SR
authors.lastname: Peterson
authors.forename: P L
authors.initials: PL
authors.lastname: Stewart
mesh_terms: D020285:Cryoelectron Microscopy; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D006367:HeLa Cells; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008958:Models, Molecular; D009687:Nuclear Proteins; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases