title: Positively charged residues at the N-terminal arm of the homeodomain are required for efficient DNA binding by homeodomain-leucine zipper proteins.
abstract: Plant homeodomain-leucine zipper proteins, unlike most animal homeodomains, bind DNA efficiently only as dimers. In the present work, we report that the deletion of the homeodomain N-terminal arm (first nine residues) of the homeodomain-leucine zipper protein Hahb-4 dramatically affects its DNA-binding affinity, causing a 70-fold increase in dissociation constant. The addition of the N-terminal arm of Drosophila Antennapedia to the truncated form restores the DNA-binding affinity of dimers to values similar to those of the native form. However, the Antennapedia N-terminal arm is not able to confer increased binding affinity to monomers of Hahb-4 lacking the leucine zipper motif, indicating that the inefficient binding of monomers must be due to structural differences in other parts of the molecule. The construction of proteins with modifications at residues 5 to 7 of the homeodomain suggests strongly that positively charged amino acids at these positions play essential roles in determining the DNA-binding affinity. However, the effect of mutations at positions 6 and 7 can be counteracted by introducing a stretch of positively charged residues at positions 1 to 3 of the homeodomain. Sequence comparisons indicate that all homeodomain-leucine zipper proteins might use contacts of the N-terminal arm with DNA for efficient binding. The occurrence of a homeodomain with a DNA-interacting N-terminal arm must then be an ancient acquisition in evolution, earlier than the separation of lines leading to metazoa, fungi and plants.
authors: Cátedra de Biología Celular y Molecular, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, CC 242 Paraje El Pozo, Santa Fe, 3000, Argentina.
authors: C M
authors: CM
authors: Palena
authors: A E
authors: AE
authors: Tron
authors: C W
authors: CW
authors: Bertoncini
authors: D H
authors: DH
authors: Gonzalez
authors: R L
authors: RL
authors: Chan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051943:Antennapedia Homeodomain Protein; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D019143:Evolution, Molecular; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D055672:Static Electricity; D013816:Thermodynamics; D014157:Transcription Factors
chemical_list: D051943:Antennapedia Homeodomain Protein; C497974:Antp protein, Drosophila; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D004247:DNA