Bacillus licheniformis BlaR1 L3 loop is a zinc metalloprotease activated by self-proteolysis.

In Bacillus licheniformis 749/I, BlaP β-lactamase is induced by the presence of a β-lactam antibiotic outside the cell. The first step in the induction mechanism is the detection of the antibiotic by the membrane-bound penicillin receptor BlaR1 that is composed of two functional domains: a carboxy-terminal domain exposed outside the cell, which acts as a penicillin sensor, and an amino-terminal domain anchored to the cytoplasmic membrane, which works as a transducer-transmitter. The acylation of BlaR1 sensor domain by the antibiotic generates an intramolecular signal that leads to the activation of the L3 cytoplasmic loop of the transmitter by a single-point cleavage.

The fate of the BlaI repressor during the induction of the Bacillus licheniformis BlaP beta-lactamase.

The induction of the Staphylococcus aureus BlaZ and Bacillus licheniformis 749/I BlaP beta-lactamases by beta-lactam antibiotics occurs according to similar processes. In both bacteria, the products of the blaI and blaRl genes share a high degree of sequence homology and act as repressors and penicillin-sensory transducers respectively. It has been shown in S.