Nucleic Acids Research Advance Access originally published online on June 18, 2007
Nucleic Acids Research 2007 35(13):4384-4395; doi:10.1093/nar/gkm448
Nucleic Acids Research, 2007, Vol. 35, No. 13 4384-4395
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Structural Biology |
Conformational and thermodynamic changes of the repressor/DNA operator complex upon monomerization shed new light on regulation mechanisms of bacterial resistance against β-lactam antibiotics
1Institut de Biologie Structurale Jean-Pierre Ebel CEA-CNRS-UJF, 41 Avenue Jules Horowitz, 38027 Grenoble Cedex 1, France, 2Centre d’Ingénierie des Protéines, Institut de Chimie B6A, Université de Liège Sart-Tilman B4000, Belgium and 3Cátedra de Microbiología, Facultad de Farmacia y Bioquímica Universidad de Buenos Aires, Junín 954 (1113), Buenos Aires, Argentina
*To whom correspondence should be addressed. Tel: +33-4-38785799; Fax: +33-4-38785494; Email: jean-pierre.simorre{at}ibs.fr
Received April 11, 2007. Revised May 16, 2007. Accepted May 18, 2007.
In absence of β-lactam antibiotics, BlaI and MecI homodimeric repressors negatively control the expression of genes involved in β-lactam resistance in Bacillus licheniformis and in Staphylococcus aureus. Subsequently to β-lactam presence, BlaI/MecI is inactivated by a single-point proteolysis that separates its N-terminal DNA-binding domain to its C-terminal domain responsible for its dimerization. Concomitantly to this proteolysis, the truncated repressor acquires a low affinity for its DNA target that explains the expression of the structural gene for resistance. To understand the loss of the high DNA affinity of the truncated repressor, we have determined the different dissociation constants of the system and solved the solution structure of the B. licheniformis monomeric repressor complexed to the semi-operating sequence OP1 of blaP (1/2OP1blaP) by using a de novo docking approach based on inter-molecular nuclear Overhauser effects and chemical-shift differences measured on each macromolecular partner. Although the N-terminal domain of the repressor is not subject to internal structural rearrangements upon DNA binding, the molecules adopt a tertiary conformation different from the crystallographic operator–repressor dimer complex, leading to a 30° rotation of the monomer with respect to a central axis extended across the DNA.
These results open new insights for the repression and induction mechanisms of bacterial resistance to β-lactams.