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  • Title: Crystal structure of the sensor domain of the BlaR penicillin receptor from Bacillus licheniformis.
    Author: Kerff F, Charlier P, Colombo ML, Sauvage E, Brans A, Frère JM, Joris B, Fonzé E.
    Journal: Biochemistry; 2003 Nov 11; 42(44):12835-43. PubMed ID: 14596597.
    Abstract:
    As in several staphylococci, the synthesis of the Bacillus licheniformis 749/I beta-lactamase is an inducible phenomenon regulated by a signal-transducing membrane protein BlaR. The C-terminal domain of this multimodular protein is an extracellular domain which specifically recognizes beta-lactam antibiotics. When it binds a beta-lactam, a signal is transmitted by the transmembrane region to the intracellular loops. In response, the hydrolytic activity of the BlaR large cytoplasmic L3 loop is induced, and a cascade of reactions is generated, leading to the transcription of the beta-lactamase gene. Here, we describe the crystal structure of the extracellular penicillin-receptor domain of BlaR (residues 346-601) at 2.5 A resolution in order to understand why this domain, whose folding is very similar to that of class D beta-lactamases, behaves as a highly sensitive penicillin-binding protein rather than a beta-lactamase. Two residues of the BlaR C-terminal domain, Thr452 and Thr542, modify the hydrophobic characteristic of the class D beta-lactamase active site. Both residues seem to be in part responsible for the lack of beta-lactamase activity of the BlaR protein due to the stability of the acyl-enzyme. Although further experimental data are needed to fully understand the transmembrane induction process, the comparison of the BlaR sensor domain structure with those of class D beta-lactamase complexes and penicillin-binding proteins provides interesting elements to hypothesize on possible signal transmission mechanisms.
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