Crystal structure of metagenome‐derived LC9‐RNase H1 with atypical DEDN active site motif

The crystal structure of metagenome‐derived LC9‐RNase H1 was determined. The structure‐based mutational analyses indicated that the active site motif of LC9‐RNase H1 is altered from DEDD to DEDN. In this motif, the location of the second glutamate residue is moved from αA‐helix to β1‐strand immediately next to the first aspartate residue, as in the active site of RNase H2. However, the structure and enzymatic properties of LC9‐RNase H1 highly resemble those of RNase H1, instead of RNase H2. We propose that LC9‐RNase H1 represents bacterial RNases H1 with an atypical DEDN active site motif, which are evolutionarily distinct from those with a typical DEDD active site motif.