title: A small protein inhibits proliferating cell nuclear antigen by breaking the DNA clamp.
abstract: Proliferating cell nuclear antigen (PCNA) forms a trimeric ring that encircles duplex DNA and acts as an anchor for a number of proteins involved in DNA metabolic processes. PCNA has two structurally similar domains (I and II) linked by a long loop (inter-domain connector loop, IDCL) on the outside of each monomer of the trimeric structure that makes up the DNA clamp. All proteins that bind to PCNA do so via a PCNA-interacting peptide (PIP) motif that binds near the IDCL. A small protein, called TIP, binds to PCNA and inhibits PCNA-dependent activities although it does not contain a canonical PIP motif. The X-ray crystal structure of TIP bound to PCNA reveals that TIP binds to the canonical PIP interaction site, but also extends beyond it through a helix that relocates the IDCL. TIP alters the relationship between domains I and II within the PCNA monomer such that the trimeric ring structure is broken, while the individual domains largely retain their native structure. Small angle X-ray scattering (SAXS) confirms the disruption of the PCNA trimer upon addition of the TIP protein in solution and together with the X-ray crystal data, provides a structural basis for the mechanism of PCNA inhibition by TIP.
authors.affiliation: Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA.
authors.forename: Amanda S
authors.initials: AS
authors.lastname: Altieri
authors.affiliation: Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Ladner
authors.affiliation: Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA Third Institute of Oceanography, State Oceanic Administration, 184 Daxue Road, Xiamen, Fujian 361005, China.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Li
authors.affiliation: National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Howard
authors.initials: H
authors.lastname: Robinson
authors.affiliation: Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA Biomolecular Labeling Laboratory, Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA.
authors.forename: Zahur F
authors.initials: ZF
authors.lastname: Sallman
authors.affiliation: Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Marino
authors.affiliation: Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA Biomolecular Labeling Laboratory, Institute for Bioscience and Biotechnology Research, University of Maryland and the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, MD 20850, USA zkelman@umd.edu.
authors.forename: Zvi
authors.initials: Z
authors.lastname: Kelman
mesh_terms: D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D000072417:Protein Domains; D019712:Thermococcus / Q000737:chemistry / Q000378:metabolism
chemical_list: D010455:Peptides; D018809:Proliferating Cell Nuclear Antigen; C521715:pepBs1-Ac peptide; D004247:DNA