title: Activation of BlaR1 protein of methicillin-resistant Staphylococcus aureus, its proteolytic processing, and recovery from induction of resistance.
abstract: The fates of BlaI, the gene repressor protein for the bla operon, BlaR1, the β-lactam sensor/signal transducer, and PC1 β-lactamase in four strains of Staphylococcus aureus upon exposure to four different β-lactam antibiotics were investigated as a function of time. The genes for the three proteins are encoded by the bla operon, the functions of which afford inducible resistance to β-lactam antibiotics in S. aureus. BlaR1 protein is expressed at low copy number. Acylation of the sensor domain of BlaR1 by β-lactam antibiotics initiates signal transduction to the cytoplasmic domain, a zinc protease, which is activated and degrades BlaI. This proteolytic degradation derepresses transcription of all three genes, resulting in inducible resistance. These processes take place within minutes of exposure to the antibiotics. The BlaR1 protein was shown to undergo fragmentation in three S. aureus strains within the time frame relevant for manifestation of resistance and was below the detection threshold in the fourth. Two specific sites of fragmentation were identified, one cytoplasmic and the other in the sensor domain. This is proposed as a means for turnover, a process required for recovery from induction of resistance in S. aureus in the absence of the antibiotic challenge. In S. aureus not exposed to β-lactam antibiotics (i.e. not acylated by antibiotic) the same fragmentation of BlaR1 is still observed, including the shedding of the sensor domain, an observation that leads to the conclusion that the sites of proteolysis might have evolved to predispose the protein to degradation within a set period of time.
authors: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556.
authors: Leticia I
authors: LI
authors: Llarrull
authors: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556.
authors: Marta
authors: M
authors: Toth
authors: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556.
authors: Matthew M
authors: MM
authors: Champion
authors: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556. Electronic address: mobashery@nd.edu.
authors: Shahriar
authors: S
authors: Mobashery
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D003593:Cytoplasm / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D004789:Enzyme Activation; D008666:Metalloendopeptidases / Q000235:genetics / Q000378:metabolism*; D055624:Methicillin-Resistant Staphylococcus aureus / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D013211:Staphylococcus aureus / Q000235:genetics* / Q000378:metabolism; D001618:beta-Lactamases / Q000378:metabolism; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D047090:beta-Lactams; C569108:BlaR1 protein, Staphylococcus aureus; D008666:Metalloendopeptidases; D001618:beta-Lactamases