Structure of Escherichia coli uracil-DNA glycosylase and its complexes with nonhydrolyzable substrate analogues in solution studied by synchrotron small-angle X-ray scattering

The structure of native and modified uracil-DNA glycosylase from E. coli in solution was studied by synchrotron small-angle X-ray scattering. The modified enzyme (6His-uracil glycosylase) differs from the native one by the presence of an additional N-terminal 11-meric sequence of amino acid residues, including a block of six His residues. In contrast to minimal differences in the amino acid sequences and functional activity, conformations of native and 6His-uracil glycosylases in solution were found to differ substantially at moderate ionic strength (60 mM NaCl). The structure of uracil-DNA glycosylase in solution is close to that in crystal and shows a tendency toward association. The interaction of this enzyme with nonhydrolyzable analogues of DNA ligands causes partial dissociation of associates and compaction of protein structure. At the same time, 6His-uracil DNA glycosylase has a compact structure, intrinsically different from that in crystals. A decrease in the ionic strength of solution results in a partial destruction of the compact structure of the modified protein, keeping its functional activity unchanged.