Three-dimensional structure of the ribonuclease T1 X 3'-guanylic acid complex at 2.6 A resolution.

The mother enzyme of RNase T1 was co-crystallized with its natural product, 3'-GMP at pH 4.0. The X-ray structure of this complex was refined with 2432 reflections in the 5.4-2.6 A range using a stereochemical restrained method (conventional R = 27.4%). The overall polypeptide chain folding is very similar in the secondary structure elements to the RNase T1 in the complex with 2'-GMP crystallized also at pH 4.0, but larger conformational changes occur in the loop regions. The base recognition scheme is identical in both complexes but in RNase T1 X 3'-GMP, the ribose phosphate is not seen in the electron density, probably due to static disorder.