page_title: BglII
section_title: Structure
hierarchical_section_title: BglII / Structure
caption_attribution_description: English: BglII-DNA complex
context_page_description: BglII is a type II restriction endonuclease isolated from certain strains of Bacillus globigii.
  The principal function of restriction enzymes is the protection of the host genome against foreign DNA, but they may also have some involvement in recombination and transposition.
  Like most type II restriction enzymes, BglII consists of two identical subunits that form a homodimer around the DNA double helix. Each monomer is 223 amino acids and symmetrically bind both sides of the unique palindromic nucleotide sequence AGATCT, cleaving the scissile phosphodiester bond between the first Adenine and Guanine nucleotides on both strands of the DNA molecule, creating sticky ends with 5' end overhangs.
  Being a type II restriction enzyme, BglII does not require ATP for its enzymatic function, but only requires association with a divalent metal cation, most likely Mg²⁺.
context_section_description: Although restriction endonucleases show little sequence similarity, crystal structures reveal that they all share a highly similar α/β core consisting of a six-stranded β-sheet flanked by five α-helices, two of which mediate dimerization. This core carries the active site (catalytic center) and the residues that contact DNA in the major groove. BglII is unique in that its α/β core is augmented by a β-sandwich subdomain that has several projections that extend outward to grip the DNA, allowing BglII to completely encircle the DNA molecule. This atypical feature of BglII suggests a unique hinge motion for DNA binding and release.
  Comparative structural studies of the free enzyme vs. the BglII-DNA complex showed that the enzyme opens by a dramatic scissor-like motion, accompanied by a complete rearrangement of the α-helices at the dimer interface. These structural studies also revealed that within each monomer a set of residues lowers or raises to alternatively sequester or expose the active site residues. These dramatic differences in structure in the free vs. bound enzyme have yet to be observed in any other restriction endonuclease and may possibly represent a novel mechanism for capturing DNA that may extend to other proteins that encircle DNA.
caption: PDB Code: 1DFM. Crystal Structure of BglII complexed with DNA at a resolution of 1.5Å [1]
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