Catalytic domain of type II restriction endonucleases BfiI and NgoFVII, and uncharacterized proteins with a DEAD domain
Catalytic domain of type II restriction endonucleases BfiI and NgoFVII, uncharacterized type III restriction endonuclease Res subunit, and uncharacterized DNA/RNA helicase superfamily II members. Proteins in this family are found mainly in prokaryotes. They contain one copy of the conserved HKD motif (H-x-K-x(4)-D, where x represents any amino acid residue) in a single polypeptide chain, and have been classified as members of the phospholipase D (PLD, EC 3.1.4.4) superfamily. BfiI consists of two discrete domains with distinct functions: an N-terminal catalytic domain with non-specific nuclease activity and dimerization function that is more closely related to Nuc, an EDTA-resistant nuclease from the phospholipase D (PLD) superfamily; and a C-terminal domain that specifically recognizes its target sequences, 5'-ACTGGG-3'. BfiI forms a functionally active homodimer which has two DNA-binding surfaces located at the C-terminal domains but only one active site, located at the dimer interface between the two N-terminal catalytic domains that contain the two HKD motifs from both subunits. BfiI utilizes a single active site to cut both DNA strands, which represents a novel mechanism for the scission of double-stranded DNA. It uses a histidine residue from the HKD motif in one subunit as the nucleophile for the cleavage of the target phosphodiester bond in both of the anti-parallel DNA strands, while the symmetrically-related histidine residue from the HKD motif of the opposite subunit acts as the proton donor/acceptor during both strand-scission events.
Jiyao W et al.(2023). "The conserved domain database in 2023.",