title: A role of basic residues and the putative intercalating phenylalanine of the HMG-1 box B in DNA supercoiling and binding to four-way DNA junctions.
abstract: HMG (high mobility group) 1 is a chromosomal protein with two homologous DNA-binding domains, the HMG boxes A and B. HMG-1, like its individual HMG boxes, can recognize structural distortion of DNA, such as four-way DNA junctions (4WJs), that are very likely to have features common to their natural, yet unknown, cellular binding targets. HMG-1 can also bend/loop DNA and introduce negative supercoils in the presence of topoisomerase I in topologically closed DNAs. Results of our gel shift assays demonstrate that mutation of Arg(97) within the extended N-terminal strand of the B domain significantly (>50-fold) decreases affinity of the HMG box for 4WJs and alters the mode of binding without changing the structural specificity for 4WJs. Several basic amino acids of the extended N-terminal strand (Lys(96)/Arg(97)) and helix I (Arg(110)/Lys(114)) of the B domain participate in DNA binding and supercoiling. The putative intercalating hydrophobic Phe(103) of helix I is important for DNA supercoiling but dispensable for binding to supercoiled DNA and 4WJs. We conclude that the B domain of HMG-1 can tolerate substitutions of a number of amino acid residues without abolishing the structure-specific recognition of 4WJs, whereas mutations of most of these residues severely impair the topoisomerase I-mediated DNA supercoiling and change the sign of supercoiling from negative to positive.
authors.affiliation: Institute of Biophysics, Academy of Sciences of the Czech Republic, CZ-612 65 Brno, Czech Republic. stros@ibp.cz
authors.forename: M
authors.initials: M
authors.lastname: Stros
authors.forename: E
authors.initials: E
authors.lastname: Muselíková
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001120:Arginine / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004278:DNA, Superhelical / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004587:Electrophoresis, Agar Gel; D024243:HMGB1 Protein; D006609:High Mobility Group Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007364:Intercalating Agents / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009690:Nucleic Acid Conformation; D010446:Peptide Fragments; D010649:Phenylalanine / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D055672:Static Electricity
chemical_list: D002352:Carrier Proteins; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D024243:HMGB1 Protein; D006609:High Mobility Group Proteins; D007364:Intercalating Agents; D010446:Peptide Fragments; D011994:Recombinant Proteins; D010649:Phenylalanine; D001120:Arginine; D004264:DNA Topoisomerases, Type I