Three-dimensional structure of ribonuclease Ms*3'-guanylic acid complex at 2.5 A resolution

The crystal structure of ribonuclease Ms*3'-guanylic acid complex has been determined by molecular replacement methods based on the known structure of ribonuclease T1. The pattern of hydrogen-bonds between the enzyme and the guanine base is similar to that discovered by Arni et al. [( 1988) J. Biol. Chem. 263, 15358-15368] in the crystal structure of ribonuclease T1*2'-guanylic acid complex. As for the possible general base in the trans-phosphorylation step of the catalysis, 0 epsilon 1 of Glu57 is within the hydrogen-bond distance (2.7 A) of the 2'-0 of the nucleotide while N epsilon 2 of His39 is significantly more distant (3.4 A) from the 2'-0.