Structural changes induced by binding of the high-mobility group I protein to a mouse satellite DNA sequence.
Using spectroscopic methods, we have studied the structural changes induced in both protein and DNA upon binding of the High-Mobility Group I (HMG-I) protein to a 21-bp sequence derived from mouse satellite DNA. We show that these structural changes depend on the stoichiometry of the protein/DNA complexes formed, as determined by Job plots derived from experiments using pyrene-labeled duplexes. Circular dichroism and melting temperature experiments extended in the far ultraviolet range show that while native HMG-I is mainly random coiled in solution, it adopts a beta-turn conformation upon forming a 1:1 complex in which the protein first binds to one of two dA.dT stretches present in the duplex. HMG-I structure in the 1:1 complex is dependent on the sequence of its DNA target. A 3:1 HMG-I/DNA complex can also form and is characterized by a small increase in the DNA natural bend and/or compaction coupled to a change in the protein conformation, as determined from fluorescence resonance energy transfer (FRET) experiments. In addition, a peptide corresponding to an extended DNA-binding domain of HMG-I induces an ordered condensation of DNA duplexes. Based on the constraints derived from pyrene excimer measurements, we present a model of these nucleated structures. Our results illustrate an extreme case of protein structure induced by DNA conformation that may bear on the evolutionary conservation of the DNA-binding motifs of HMG-I. We discuss the functional relevance of the structural flexibility of HMG-I associated with the nature of its DNA targets and the implications of the binding stoichiometry for several aspects of chromatin structure and gene regulation.
Slama-Schwok
A
A
INRA 806/EA2703 Muséum National d'Histoire Naturelle, Institut de Biologie Physico-Chimique, Paris, France. schwok@enstay.ensta.fr
Zakrzewska
K
K
Léger
G
G
Leroux
Y
Y
Takahashi
M
M
Käs
E
E
Debey
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002942:Circular Dichroism; D004276:DNA, Satellite / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000737:chemistry* / Q000378:metabolism*; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
D004276:DNA, Satellite; D006609:High Mobility Group Proteins; D046911:Macromolecular Substances; D010455:Peptides