       Document 0142
 DOCN  M9440142
 TI    Crystal structure of Escherichia coli RNase HI in complex with Mg2+ at
       2.8 A resolution: proof for a single Mg(2+)-binding site.
 DT    9404
 AU    Katayanagi K; Okumura M; Morikawa K; Protein Engineering Research
       Institute, Osaka, Japan.
 SO    Proteins. 1993 Dec;17(4):337-46. Unique Identifier : AIDSLINE
       MED/94151286
 AB    To obtain more precise insight into the Mg(2+)-binding site essential
       for RNase HI catalytic activity, we have determined the crystal
       structure of E. coli RNase HI in complex with Mg2+. The analyzed
       cocrystal, which is not isomorphous with the Mg(2+)-free crystal
       previously refined at 1.48 A resolution, was grown at a high MgSO4
       concentration more than 100 mM so that even weakly bound Mg2+ sites
       could be identified. The structure was solved by the molecular
       replacement method, using the Mg(2+)-free crystal structure as a search
       model, and was refined to give a final R-value of 0.190 for intensity
       data from 10 to 2.8 A, using the XPLOR and PROLSQ programs. The backbone
       structures are in their entirety very similar to each other between the
       Mg(2+)-bound and the metal-free crystals, except for minor regions in
       the enzyme interface with the DNA/RNA hybrid. The active center clearly
       revealed a single Mg2+ atom located at a position almost identical to
       that previously found by the soaking method. Although the two metal-ion
       mechanism had been suggested by another group (Yang, W., Hendrickson,
       W.A., Crouch, R.J., Satow, Y. Science 249:1398-1405, 1990) and partially
       supported by the crystallographic study of inactive HIV-1 RT RNase H
       fragment (Davies, J.F., II, Hostomska, Z., Hostomsky, Z., Jordan, S.R.,
       Matthews, D. Science 252:88-95, 1991), the present result excludes the
       possibility that RNase HI requires two metal-binding sites for activity.
       In contrast to the features in the metal-free enzyme, the side chains of
       Asn-44 and Glu-48 are found to form coordinate bonds with Mg2+ in the
       metal-bound crystal.
 DE    Binding Sites  Crystallography  Escherichia coli/*ENZYMOLOGY
       Magnesium/*METABOLISM  Models, Molecular  Ribonuclease H, Calf
       Thymus/*CHEMISTRY/PHYSIOLOGY  Support, Non-U.S. Gov't  JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).

