Integral membrane protein involved in sensing of the presence of beta-lactam antibiotics and transduction of the information to the cytoplasm. Mechanistically, activation of the signal transducer involves acylation of a serine in the C-terminal sensor domain upon binding of the beta-lactam antibiotic. In turn, a conformational change occurs and the signal is transmitted from the cell surface to the cytoplasm. There, the zinc protease domain is activated and initiates autoproteolysis as well as cleavage of the transcriptional repressor BlaI leading to derepression of antibiotic resistance genes. Carboxylation occurs on two lysine residues. Carboxylation at 'Lys-405' activates the active site serine residue for acylation. On acylation, the lysine side chain experiences a spontaneous decarboxylation that entraps the sensor in its activated state. Belongs to the peptidase M56 family.