In addition to Glu56 and His86, which are the principal catalytic residues, an important role in the first reaction step of RNA cleavage also seems to be played by Arg67 and Arg71, which are located in the phosphate-binding site and form hydrogen bonds with the oxygens of the phosphate group of the mononucleotides. Their positive charge deficiency on the phosphorus atom and facilitating nucleophilic attack very likely causes polarization of the bonds between the oxygens and the phosphorus atom, leading to electron by O2 of the ribose on the phosphorus atom, leading to cyclophosphate formation. The negatively charged Glu56 is in position to attract the proton from O2 of the ribose
Please wait a moment until the data is sorted. This message will disappear when the data is sorted.
vapor diffusion, hanging drop, 298 K, ammonium sulfate, phosphate buffer, pH 7.2, structure with free active site, resolution 1.8 A, crystal structure of ribonuclease Sa2 with exo-2’,3’-cyclophosphorotioate, a product of the reaction, resolution 2.20 A, crystal structure of ribonuclease Sa2 with guanosine 3’-monophosphate obtained by ligand diffusion, resolution 2.20 A, crystal structure of ribonuclease Sa2 with guanosine-3’-cyclophosphate prepared by cocrystallization, resolution 2.25 A, crystal structure of ribonuclease Sa2 with guanosine-2’-cyclophosphate, resolution 1.8 A, the crystals are monoclinic and belong to the C2 space group