Molecule of the Month: DNA Helicase
DNA helicase pries apart the two strands in a DNA double helix, powered by ATP
Exploring the Structure
DNA Helicase and Loader (PDB entry 4m4w)
A second protein, a helicase loader, assists the initiator and chaperones the replicative DNA helicase onto the single strand. The structure shown here (PDB entry 4m4w ) includes DNA helicase (blue), a helicase loader (magenta) and a small domain from primase (green), the enzyme that will build the short RNA primer that gets replication started. This low-resolution structure was solved using atomic-resolution structures of the individual components, and shows an evocative gap in the ring of helicase subunits which may be site of entry of the single strand of DNA. To explore this structure in more detail, click on the image for an interactive Jmol.
Topics for Further Discussion
- Several other structures of helicases bound to single-stranded DNA are available in the PDB, including the bacterial DNA helicase Rep that acts as a dimer (entry 1uaa).
- DnaA has a domain that binds to double-stranded DNA, wrapping it around the outside of the DnaA assembly. A structure of this domain bound to double-stranded DNA is available in PDB entry 1j1v.
- The structure of the helicase loader DnaC is remarkably similar to the structure of DnaA, forming a similar helix of subunits. You can use the "Compare Structures" tool to overlap these two structures, in PDB entries 3ecc and 3r8f.
Related PDB-101 Resources
- Browse Protein Synthesis
- 4m4w: B. Liu, W. K. Eliason & T. A. Steitz (2013) Structure of a helicase-helicase loader complex reveals insights into the mechanism of bacterial primosome assembly. Nature Communications 4: 2495.
- 4esv: O. Itsathitphaisarn, R. A. Wing, W. K. Eliason, J. Wang & T. Steitz (2012) The hexameric helicase DnaB adopts a nonplanar conformation during translocation. Cell 151, 267-277.
- P. Soultanas (2012) Loading mechanisms of ring helicases at replication origins. Molecular Microbiology 84, 6-16.
- 3r8f: K. E. Duderstadt, K. Chuang & J. M. Berger (2011) DNA stretching by bacterial initiators promotes replication origin opening. Nature 478, 209-213.
December 2013, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2013_12