5a9k

Structural basis for DNA strand separation by a hexameric replicative helicaseStructural basis for DNA strand separation by a hexameric replicative helicase

5a9k, resolution 19.00Å Show:Asymmetric Unit Biological Assembly Structural highlights 5a9k is a 6 chain structure with sequence from Bovine papillomavirus. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Ligands: Related: 5a9l, 5a9m, 5a9n, 5a9o Activity: DNA helicase, with EC number 3.6.4.12 Experimental data: Check Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function [VE1_BPV1] ATP-dependent DNA helicase required for initiation of viral DNA replication. It forms a complex with the viral E2 protein. The E1-E2 complex binds to the replication origin which contains binding sites for both proteins. Publication Abstract from PubMed Hexameric helicases are processive DNA unwinding machines but how they engage with a replication fork during unwinding is unknown. Using electron microscopy and single particle analysis we determined structures of the intact hexameric helicase E1 from papillomavirus and two complexes of E1 bound to a DNA replication fork end-labelled with protein tags. By labelling a DNA replication fork with streptavidin (dsDNA end) and Fab (5' ssDNA) we located the positions of these labels on the helicase surface, showing that at least 10 bp of dsDNA enter the E1 helicase via a side tunnel. In the currently accepted 'steric exclusion' model for dsDNA unwinding, the active 3' ssDNA strand is pulled through a central tunnel of the helicase motor domain as the dsDNA strands are wedged apart outside the protein assembly. Our structural observations together with nuclease footprinting assays indicate otherwise: strand separation is taking place inside E1 in a chamber above the helicase domain and the 5' passive ssDNA strands exits the assembly through a separate tunnel opposite to the dsDNA entry point. Our data therefore suggest an alternative to the current general model for DNA unwinding by hexameric helicases. Structural basis for DNA strand separation by a hexameric replicative helicase.,Chaban Y, Stead JA, Ryzhenkova K, Whelan F, Lamber EP, Antson A, Sanders CM, Orlova EV Nucleic Acids Res. 2015 Aug 3. pii: gkv778. PMID:26240379 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.