Evidence of an Intramolecular Interaction between the Two Domains of the BlaR1 Penicillin Receptor during the Signal Transduction

Sophie Hanique, Maria-Luigi Colombo, Erik Goormaghtigh, Patrice Soumillion, Jean-Marie Frère, Bernard Joris
2004 Journal of Biological Chemistry  
The BlaR1 protein is a penicillin-sensory transducer involved in the induction of the Bacillus licheniformis ␤-lactamase. The amino-terminal domain of the protein exhibits four transmembrane segments (TM1-TM4) that form a four-␣-helix bundle embedded in the plasma bilayer. The carboxyl-terminal domain of 250 amino acids (BlaR-CTD) fused at the carboxyl end of TM4 possesses the amino acid sequence signature of penicillin-binding proteins. This membrane topology suggests that BlaR-CTD and the
more » ... laR-CTD and the BlaR-amino-terminal domain are responsible for signal reception and signal transduction, respectively. With the use of phage display experiments, we highlight herein an interaction between BlaR-CTD and the extracellular, 63-amino acid L2 loop connecting TM2 and TM3. This interaction does not occur in the presence of penicillin. This result suggests that binding of the antibiotic to BlaR1 might entail the release of the interaction between L2 and BlaR-CTD, causing a motion of the ␣-helix bundle and transfer of the information to the cytoplasm of the cell. In addition, fluorescence spectroscopy, CD, and Fourier transform IR spectroscopy experiments indicate that in contrast to the behavior of the corresponding Staphylococcus aureus protein, the ␤-lactam antibiotic does not induce a drastic conformational change in B. licheniformis BlaR-CTD. Bacillus licheniformis 749/I and Staphyloccocus aureus PC1 secrete BlaP and BlaZ ␤-lactamases, respectively, the synthesis of which is induced by the presence of an exogenous ␤-lactam antibiotic, the inducer (1, 2). In both strains, at least three regulatory genes, blaI, blaR1, and blaR2, are involved in the derepression of the blaP or blaZ genes. The blaI gene encodes a cytoplasmic repressor that, in the absence of antibiotic, maintains a low level of ␤-lactamase expression (3, 4). The blaR1 1 The abbreviations used are: PBP, penicillin-binding protein; NTD, amino-terminal domain; CTD, carboxyl-terminal domain; TM, transmembrane; ELISA, enzyme-linked immunosorbent assay; PBS, phosphate-buffered saline; 6-APA, 6-aminopenicillanic acid; FT, Fourier transform.
doi:10.1074/jbc.m313488200 pmid:14736870 fatcat:2y5zaib2rrckzbnezhvmjgyhxm