title: DNA bending by bHLH charge variants.
abstract: We wish to understand the role of electrostatics in DNA stiffness and bending. The DNA charge collapse model suggests that mutual electrostatic repulsions between neighboring phosphates significantly contribute to DNA stiffness. According to this model, placement of fixed charges near the negatively charged DNA surface should induce bending through asymmetric reduction or enhancement of these inter-phosphate repulsive forces. We have reported previously that charged variants of the elongated basic-leucine zipper (bZIP) domain of Gcn4p bend DNA in a manner consistent with this charge collapse model. To extend this result to a more globular protein, we present an investigation of the dimeric basic-helix-loop-helix (bHLH) domain of Pho4p. The 62 amino acid bHLH domain has been modified to position charged amino acid residues near one face of the DNA double helix. As observed for bZIP charge variants, DNA bending toward appended cations (away from the protein:DNA interface) is observed. However, unlike bZIP proteins, DNA is not bent away from bHLH anionic charges. This finding can be explained by the structure of the more globular bHLH domain which, in contrast to bZIP proteins, makes extensive DNA contacts along the binding face.
authors.affiliation: Medical Scientist Training Program, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: McDonald
authors.forename: Jason D
authors.initials: JD
authors.lastname: Kahn
authors.forename: L James
authors.initials: LJ
authors.lastname: Maher
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018257:Helix-Loop-Helix Motifs; D008958:Models, Molecular; D016296:Mutagenesis; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D017510:Protein Folding; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055672:Static Electricity; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004247:DNA; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C060292:PHO4 protein, S cerevisiae