Non-cognizable ribonucleotide, 2'AMP, binds to a mutant ribonuclease T1 (Y45W) at a new base-binding site but not at the guanine-recognition site.

Complex of a mutant ribonuclease T1 (Y45W) with a non-cognizable ribonucleotide, 2'AMP, has been determined and refined by X-ray diffraction at 1.7 A resolution. The 2'AMP molecule locates at a new base-binding site which is remote from the guanine-recognition site, where 2'GMP was found to be bound. The nucleotide adopts the anti conformation of the glycosidic bond and C3'-exo sugar pucker. There exists a single hydrogen bond between the adenine base and the enzyme, and, therefore, the site found is apparently a non-specific binding site. The results indicate that the binding of 2'AMP to the guanine-recognition site is weaker than that to the new binding site.