title: [X-ray structural analysis of magnesium-containing Serratia marcescens endonuclease].
abstract: The three-dimensional crystal structure of the DNA/RNA nonspecific endonuclease from Serratia marcescens was refined at the resolution of 1.07 A to R factor of 12.4% and Rfree factor of 15.3% using the anisotropic approximation. The structure includes 3924 non-hydrogen atoms, 715 protein-bound water molecules, and a Mg2+ ion in each binding site of each subunit of the nuclease homodimeric globular molecule. The 3D topological model of the enzyme was revealed, the inner symmetry of the monomers in its N- and C-termini was found, and the local environment of the magnesium cofactor in the nuclease active site was defined. Mg2+ ion was found to be bound to the Asn119 residue and surrounded by five associated water molecules that form an octahedral configuration. The coordination distances for the water molecules and the O delta 1 atom of Asn119 were shown to be within a range of 2.01-2.11 A. The thermal factors for the magnesium ion in subunits are 7.08 and 4.60 A2, and the average thermal factors for the surrounding water molecules are 11.14 and 10.30 A2, respectively. The region of the nuclease subunit interactions was localized, and the alternative side chain conformations were defined for 51 amino acid residues of the nuclease dimer.
authors.affiliation: Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, ul. Vavilova 32, Moscow, 117984 Russia.
authors.forename: S V
authors.initials: SV
authors.lastname: Shliapnikov
authors.forename: V V
authors.initials: VV
authors.lastname: Lunin
authors.forename: E V
authors.initials: EV
authors.lastname: Blagova
authors.forename: M
authors.initials: M
authors.lastname: Perbandt
authors.forename: Ch
authors.initials: Ch
authors.lastname: Betzel
authors.forename: A M
authors.initials: AM
authors.lastname: Mikhaĭlov
mesh_terms: D018360:Crystallography, X-Ray; D004706:Endodeoxyribonucleases / Q000737:chemistry*; D004722:Endoribonucleases / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D004706:Endodeoxyribonucleases; D004722:Endoribonucleases; C021835:Serratia marcescens nuclease; D008274:Magnesium