BACKBONE DYNAMICS OF ESCHERICHIA-COLI RIBONUCLEASE HI - CORRELATIONS WITH STRUCTURE AND FUNCTION IN AN ACTIVE ENZYME

Ribonuclease H is an endonuclease that hydrolyzes the RNA moiety of RNA-DNA duplex molecules. Escherichia coli ribonuclease H is involved in DNA replication, and retroviral ribonuclease H is essential for reverse transcription of the viral genome. To characterize the intramolecular dynamical properties of E. coli ribonuclease H, spin-lattice relaxation rate constants, spin-spin relaxation rate constants and steady state nuclear Overhauser effects for the N-15 nuclear spins were measured by using proton-detected heteronuclear NMR spectroscopy; The relaxation data were analyzed by using a series of dynamical models in conjunction with a statistical model selection protocol. Ribonuclease H exhibits a complex array of dynamical features, most notably in the parallel beta-strands of the principal five-stranded beta-sheet, the coiled-coil helical interface, the active site, and the loop regions surrounding the active site. The dynamical properties are correlated with local structural environments of the N-15 spins and suggest possible relationships to the functional properties of ribonuclease H. Results for E. coli ribonuclease H are compared to previously reported results for the human immunodeficiancy virus type 1 ribonuclease H domain of reverse transcriptase.