Resistance to β-Lactam Antibiotics and Its Mediation by the Sensor Domain of the Transmembrane BlaR Signaling Pathway in Staphylococcus aureus

Abstract

؊1 , yet the deacylation process was essentially irreversible within one cell cycle. The protein undergoes a significant conformational change on binding with ␤-lactam antibiotics, a process that commences at the preacylation complex and reaches its full effect after protein acylation has been accomplished. These conformational changes are likely to be central to the signal transduction events when the organism is exposed to the ␤-lactam antibiotic.

Activation of BlaR1 Protein of Methicillin-resistant Staphylococcus aureus, Its Proteolytic Processing, and Recovery from Induction of Resistance

“…Under these conditions, the increase in MIC in the presence of the purified sensor domain is due to the uncommon covalent antibiotic sequestration mechanism, documented earlier for unrelated systems (28). The sensor domain of BlaR1 is acylated by ␤-lactam antibiotics with long half-lives (3,5). The absence of multiple turnover of antibiotic explains why high concentrations of BlaR S are required for an effect on the MIC to be observed.…”

“…The process is actually quite complex. We do not discount that the longevity of the acylated surface domain of BlaR1 with different antibiotics (5) and the ability of those species individually to manifest signal transduction to varying degrees should also play a role in these processes. They do, and they contribute to differences seen with various antibiotics in general.…”

“…Its implication is that BlaR1 proteolysis is probably a means for reversal of induction. We have shown that when antibiotic acylates the sensor domain, the complex often is stable for the duration of the bacterial generation, at times much longer (5). When the challenge of antibiotic is withdrawn, by the action of ␤-lactamase or by lack of sufficient exposure, the organism has to reverse the mobilization of resistance.…”

“…BlaR S and BlaI Recombinant Proteins and Specific AntibodiesrBlaR S and rBlaI expressed in E. coli were purified as described previously (5,8). Rabbit polyclonal antibody against BlaR S (anti-BlaR S , 1.93 mg/ml) and rabbit polyclonal antibody against BlaI (anti-BlaI, 1.86 mg/ml) were generated by immunization of a rabbit with either purified rBlaR S or rBlaI protein, respectively (EZBiolab).…”

“…Antibiotic acylates the C-terminal sensor domain located on the surface of the plasma membrane by a mechanism involving a surface loop of the protein (1) and an elaborate process that leads to N-decarboxylation of a lysine within the antibiotic-binding site (2)(3)(4). The acylated species enjoys a longevity that often exceeds the doubling time of most S. aureus strains; hence, a single BlaR1 modification by the antibiotic is sufficient for the entire bacterial generation (5). It has been proposed that the cytoplasmic domain of BlaR1 is a zinc protease (6).…”