title: Allosteric signaling in the biotin repressor occurs via local folding coupled to global dampening of protein dynamics.
abstract: The biotin repressor is an allosterically regulated, site-specific DNA-binding protein. Binding of the small ligand bio-5'-AMP activates repressor dimerization, which is a prerequisite to DNA binding. Multiple disorder-to-order transitions, some of which are known to be important for the functional allosteric response, occur in the vicinity of the ligand-binding site concomitant with effector binding to the repressor monomer. In this work, the extent to which these local changes are coupled to additional changes in the structure/dynamics of the repressor was investigated using hydrogen/deuterium exchange coupled to mass spectrometry. Measurements were performed on the apo-protein and on complexes of the protein bound to four different effectors that elicit a range of thermodynamic responses in the repressor. Global exchange measurements indicate that binding of any effector to the intact protein is accompanied by protection from exchange. Mass spectrometric analysis of pepsin-cleavage products generated from the exchanged complexes reveals that the protection is distributed throughout the protein. Furthermore, the magnitude of the level of protection in each peptide from hydrogen/deuterium exchange correlates with the magnitude of the functional allosteric response elicited by a ligand. These results indicate that local structural changes in the binding site that occur concomitant with effector binding nucleate global dampening of dynamics. Moreover, the magnitude of dampening of repressor dynamics tracks with the magnitude of the functional response to effector binding.
authors.affiliation: Department of Chemistry and Biochemistry and Center for Biological Structure and Organization, College of Chemical and Life Sciences, University of Maryland, College Park, MD 20742, USA.
authors.forename: Olli
authors.initials: O
authors.lastname: Laine
authors.forename: Emily D
authors.initials: ED
authors.lastname: Streaker
authors.forename: Maryam
authors.initials: M
authors.lastname: Nabavi
authors.forename: Catherine C
authors.initials: CC
authors.lastname: Fenselau
authors.forename: Dorothy
authors.initials: D
authors.lastname: Beckett
mesh_terms: D000249:Adenosine Monophosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D041961:Deuterium Exchange Measurement; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D008024:Ligands; D012097:Repressor Proteins; C036824:biotin repressor; D000249:Adenosine Monophosphate