Time-Dependence of Activation of the bla System in Methicillin-Resistant Staphylococcus aureus; poster

LLARRULL, L.I.; TOTH, M.; CHAMPION, M. M.; MOBASHERY S.

Plymouth, Indiana

Jornada; 16th Annual Biochemistry Research Forum; 2011

Department of Chemistry and Biochemistry, University of Notre Dame

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a globally important pathogen that is resistant to virtually all commercially available beta-lactam antibiotics. The BlaR1 beta-lactam sensor/signal transducer protein of MRSA has been implicated primarily in induction of beta-lactamase expression (bla operon). BlaR1 fragmentation has been described as an event that occurs after induction of MRSA by beta-lactam antibiotics. In addition, it was shown that BlaR1 proteolysis is required for activation of the cytoplasmic domain of the protein. Here we analyzed the time course of induction of the bla system in different MRSA strains, and we show the existence of antibiotic-related variations in the duration and extent of the activation of the system. We also present data that show that BlaR1 fragmentation occurs in non-induced cells as well, and in slightly different positions in different MRSA strains and in recombinant BlaR1 expressed in E. coli, which suggests the presence of a mobile and proteolysis-prone region in the cytoplasmic domain. Our results hence suggest that BlaR1 fragmentation could be adventitious, and not necessarily part of the activation process. We have also documented that in certain MRSA strains, BlaR1 sheds its beta-lactam sensor domain to the medium upon exposure to antibiotics. This shedding in evolution of class D beta-lactamases from a progenitor penicillin-binding protein in an evolutionary time frame has been presumed.