Side chain dynamics of carboxyl and carbonyl groups in the catalytic function of Escherichia coli ribonuclease H.
Résumé
: Many proteins use Asx and Glx (x = n, p, or u) side chains as key functional groups in enzymatic catalysis and molecular recognition. In this study, NMR spin relaxation experiments and molecular dynamics (MD) simulations are used to measure the dynamics of the side chain amide and carboxyl groups, 13Cγ/δ, in Escherichia coli ribonuclease HI (RNase H). Model-free analysis shows that the catalytic residues in RNase H are pre-organized on ps-ns timescales via a network of electrostatic interactions. However, chemical exchange line broadening shows that these residues display significant conformation-al dynamics on μs - ms timescales upon binding of Mg2+ ions. Two groups of catalytic residues exhibit differential linebroadening, impli-cating distinct reorganizational processes upon binding of metal ions. These results support the "mobile metal ion" hypothesis, which was inferred from structural studies of RNase H.