3OKG: Crystal structure of HsdS subunit from Thermoanaerobacter tengcongensis

Type I DNA methyltransferases contain one specificity subunit (HsdS) and two modification subunits (HsdM). The electron microscopy model of M.EcoKI-M(2)S(1) methyltransferase shows a reasonable closed state of this clamp-like enzyme, but the structure of the open state is still unclear. The 1.95 A crystal structure of the specificity subunit from Thermoanaerobacter tengcongensis (TTE-HsdS) shows an unreported open form inter-domain orientation of this subunit. Based on the crystal structure of TTE-HsdS and the closed state model of M.EcoKI-M(2)S(1), we constructed a potential open state model of type I methyltransferase. Mutational studies indicated that two alpha-helices (aa30-59 and aa466-495) of the TTE-HsdM subunit are important inter-subunit interaction sites in the TTE-M(2)S(1) complex. DNA binding assays also highlighted the importance of the C-terminal region of TTE-HsdM for DNA binding by the TTE-M(2)S(1) complex. On the basis of structural analysis, biochemical experiments and previous studies, we propose a dynamic opening and closing mechanism for type I methyltransferase.
PDB ID: 3OKGDownload
MMDB ID: 90794
PDB Deposition Date: 2010/8/24
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 1.95  Å
Source Organism:
Similar Structures:
Biological Unit for 3OKG: monomeric; determined by author
Molecular Components in 3OKG
Label Count Molecule
Protein (1 molecule)
Restriction Endonuclease S Subunits
Molecule annotation
Chemicals (8 molecules)
* Click molecule labels to explore molecular sequence information.

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