Mutation of the conserved GRG motif anddecreasing activity of human RNase H2

RNase H2 consists of three subunits (H2A, H2B and H2C) and is involved in the hydrolysis of RNA/DNA hybrids. The GRG motif in RNase H2 is highly conserved and recognizes the ribonucleotides misincorporated into dsDNA. The mutant G37S in the GRG motif of human RNase H2A was found to be correlated with Aicardi-Goutisressyndrome (AGS). In this study, 4 mutants (G37S, G37A, R38A and G39A) were prepared and their biochemical properties of secondary structure, activity and binding affinity with substrate were studied in order to explore the function of the GRG motif. The activity assay showed that the mutations resulted in significantly decreased RNase activity. The binding efficiency assay demonstrated that binding affinities between 4 mutants and 1-ribo FAM-labeled substrate were significantly weakened. These results all indicated that the GRG motif contributes directly to substrate binding and is closely related to the enzyme activity.