Structure of a Sliding Clamp on DNA

DNA replication in archaea and eukaryotes is executed by family B DNA polymerases, which exhibit full activity when complexed with the DNA clamp, proliferating cell nuclear antigen (PCNA). This replication enzyme consists of the polymerase and exonuclease moieties responsible for DNA synthesis and editing (proofreading), respectively. Because of the editing activity, this enzyme ensures the high fidelity of DNA replication. However, it remains unclear how the PCNA-complexed enzyme temporally switches between the polymerizing and editing modes. Here, we present the threedimensional structure of the Pyrococcus furiosus DNA polymerase B-PCNA-DNA ternary complex, which is the core component of the replisome, determined by single particle electron microscopy of negatively stained samples. This structural view, representing the complex in the editing mode, revealed the whole domain configuration of the trimeric PCNA ring and the DNA polymerase, including protein-protein and protein-DNA contacts. Notably, besides the authentic DNA polymerase-PCNA interaction through a PCNAinteracting protein (PIP) box, a novel contact was found between DNA polymerase and the PCNA subunit adjacent to that with the PIP contact. This contact appears to be responsible for the configuration of the complex specific for the editing mode. The DNA was located almost at the center of PCNA and exhibited a substantial and particular tilt angle against the PCNA ring plane. The obtained molecular architecture of the complex, including the new contact found in this work, provides clearer insights into the switching mechanism between the two distinct modes, thus highlighting the functional significance of PCNA in the replication process.fidelity control | protein-DNA complex | replication fork | single particle analysis | structural bioinformatics

Section: Resultsmentioning

confidence: 51%

Architecture of the DNA polymerase B-proliferating cell nuclear antigen (PCNA)-DNA ternary complex

Mayanagi

Kiyonari

Nishida

et al. 2011

“…However, a tilted orientation was first suggested by our computational studies on PCNA/DNA binary complex (39). Experimentally, the crystal structure of the bacterial β-clamp/DNA complex (40) indicated that DNA passes through the clamp at a sharp angle of 22°. A PCNA crystal structure with a short DNA revealed the DNA at a 40°angle.…”

Section: Structural Determinants Of Flexibility For the Ternary Assemmentioning

confidence: 99%

Repair complexes of FEN1 endonuclease, DNA, and Rad9-Hus1-Rad1 are distinguished from their PCNA counterparts by functionally important stability

Querol-Audí

Cheng

et al. 2012

Processivity clamps such as proliferating cell nuclear antigen (PCNA) and the checkpoint sliding clamp Rad9/Rad1/Hus1 (9-1-1) act as versatile scaffolds in the coordinated recruitment of proteins involved in DNA replication, cell-cycle control, and DNA repair. Association and handoff of DNA-editing enzymes, such as flap endonuclease 1 (FEN1), with sliding clamps are key processes in biology, which are incompletely understood from a mechanistic point of view. We have used an integrative computational and experimental approach to define the assemblies of FEN1 with double-flap DNA substrates and either proliferating cell nuclear antigen or the checkpoint sliding clamp 9-1-1. Fully atomistic models of these two ternary complexes were developed and refined through extensive molecular dynamics simulations to expose their conformational dynamics. Clustering analysis revealed the most dominant conformations accessible to the complexes. The cluster centroids were subsequently used in conjunction with single-particle electron microscopy data to obtain a 3D EM reconstruction of the human 9-1-1/FEN1/DNA assembly at 18-Å resolution. Comparing the structures of the complexes revealed key differences in the orientation and interactions of FEN1 and double-flap DNA with the two clamps that are consistent with their respective functions in providing inherent flexibility for lagging strand DNA replication or inherent stability for DNA repair.F lap endonuclease 1 (FEN1) belongs to a class of essential nucleases (the FEN1 5′ nuclease superfamily) present in all domains of life (1). FEN1 catalyzes the endonucleolytic cleavage of bifurcated DNA or RNA structures known as 5′ flaps. These 5′ flaps are generated during lagging strand DNA synthesis or during long-patch base excision repair. The FEN1 substrates are in fact double-flap DNA (dfDNA) with DNA on the opposite side of the 5′ flap, forming a single nucleotide 3′ flap when bound to the enzyme (2, 3). By removing the 5′ ssDNA or RNA flap from such substrates, FEN1 produces a single nicked product that could be sealed by the subsequent action of a DNA ligase (4). Consistent with its crucial role in DNA replication and repair, FEN1 is highly expressed in all proliferative tissues, and its activity is key for the maintenance of genomic integrity (5). FEN1 has been identified as a cancer susceptibility gene, and mutations in it have been linked to a number of genetic diseases, such as EM map myotonic dystrophy, Huntington disease, several ataxias, fragile X syndrome, and cancer (6-10).The nuclease activity of FEN1 can be stimulated by association with processivity clamps such as proliferating cell nuclear antigen (PCNA), which encircle DNA at sites of replication and repair (11)(12)(13). PCNA is a recognized master coordinator of cellular responses to DNA damage and interacts with numerous DNA repair and cell-cycle control proteins. In this capacity, PCNA serves not only as a mobile platform for the attachment of these proteins to DNA but, importantly, plays an active role in the recru...

“…Replicative polymerases generally operate in association with a sliding clamp (e.g., the PolIII ␤-subunit) that encircles the DNA and greatly enhances processivity. The structure of DNA-bound ␤ has recently been reported (24), thus facilitating modeling with PolC (Fig. 6A).…”

Section: Structural Clues To the Evolution Of The 3 -5 Exonuclease Inmentioning

confidence: 99%

Structure of PolC reveals unique DNA binding and fidelity determinants

Evans

Davies²,

Bullard

et al. 2008

124

PolC is the polymerase responsible for genome duplication in many Gram-positive bacteria and represents an attractive target for antibacterial development. We have determined the 2.4-Å resolution crystal structure of Geobacillus kaustophilus PolC in a ternary complex with DNA and dGTP. The structure reveals nascent base pair interactions that lead to highly accurate nucleotide incorporation. A unique ␤-strand motif in the PolC thumb domain contacts the minor groove, allowing replication errors to be sensed up to 8 nt upstream of the active site. PolC exhibits the potential for large-scale conformational flexibility, which could encompass the catalytic residues. The structure suggests a mechanism by which the active site can communicate with the rest of the replisome to trigger proofreading after nucleotide misincorporation, leading to an integrated model for controlling the dynamic switch between replicative and repair polymerases. This ternary complex of a cellular replicative polymerase affords insights into polymerase fidelity, evolution, and structural diversity.DNA polymerase III ͉ DNA replication ͉ Gram-positive polymerase ͉ polymerase and histidinol phosphatase (PHP) ͉ ternary complex D NA polymerases are the enzymes responsible for DNA synthesis. Cellular organisms typically use multiple DNA polymerase types. The ''replicative'' polymerase performs the bulk of genome duplication, whereas various specialty polymerases repair damaged DNA and resolve Okazaki fragments. Across every kingdom of life, replicative polymerases exhibit certain hallmarks such as high fidelity, speed, and processivity (1). Polymerase holoenzyme accessory proteins play an integral role in achieving the extraordinary efficiency and accuracy of the replicative polymerase complex. These include a ''sliding clamp'' that encircles the DNA and increases processivity (2).Bacterial replicative polymerases comprise the C family of DNA polymerases (3) and differ significantly from the replicative polymerases of eukaryotes, bacteriophage, and archaea, which belong to the B family. The major C family replicative polymerases are DnaE (PolIII), found primarily in Gram-negative bacteria, and PolC (PolIIIC), found primarily in Gram-positive bacteria (4). Apoenzyme crystal structures of DnaE have revealed surprising structural differences in the catalytic center of the enzyme compared with B family polymerases, suggesting a separate evolutionary origin for the C family (5, 6).As the core component of the replicative polymerase complex in Gram-positive pathogens such as Staphylococcus aureus, PolC has received considerable attention as a potential target for antibacterial drug discovery (7,8). No currently marketed antibiotics target the central replication apparatus, making PolC a novel target for antibacterial development. Gram-negative and Gram-positive bacteria are separated by Ͼ1 billion years of evolution, and PolC and DnaE share Ͻ20% sequence identity; PolC is further differentiated from DnaE by domain rearrangements and by the presence of an ...