title: An extradenticle-induced conformational change in a HOX protein overcomes an inhibitory function of the conserved hexapeptide motif.
abstract: HOX homeoproteins control cell identities during animal development by differentially regulating target genes. The homeoprotein encoded by the extradenticle (exd) gene can selectively modify HOX DNA binding, suggesting that it contributes to HOX specificity in vivo. HOX-EXD interactions are in part mediated by a conserved stretch of amino acids termed the hexapeptide found in many HOX proteins. Here, we demonstrate that a 20 bp oligonucleotide from the 5' region of the mouse Hoxb-1 gene, a homolog of Drosophila labial (lab), is sufficient to direct an expression pattern in Drosophila that is very similar to endogenous lab. In vivo, this expression requires lab and exd and, in vitro, LAB requires EXD to bind this oligonucleotide. In contrast, LAB proteins with mutations in the hexapeptide bind DNA even in the absence of EXD. Moreover, a hexapeptide mutant of LAB has an increased ability to activate transcription in vivo. Partial proteolysis experiments suggest that EXD can induce a conformational change in LAB. These data are consistent with a mechanism whereby the LAB hexapeptide inhibits LAB function by inhibiting DNA binding and that an EXD-induced conformational change in LAB relieves this inhibition, promoting highly specific interactions with biologically relevant binding sites.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Chan
authors.forename: H
authors.initials: H
authors.lastname: Pöpperl
authors.forename: R
authors.initials: R
authors.lastname: Krumlauf
authors.forename: R S
authors.initials: RS
authors.lastname: Mann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D007301:Insect Hormones / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D007301:Insect Hormones; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C083405:exd protein, Drosophila; C059843:lab protein, Drosophila; D004247:DNA