Mechanism of regulation of flotillin levels by the staphylococcal accessory regulator SarA

Resumo

Bacteria organize many cellular processes into functional membrane microdomains (FMM) similar to the eukaryotic lipid rafts. Flotillins, the structural proteins of the FMM, have a crucial role in the subcellular compartmentalization of important processes, such as virulence, antibiotic resistance, cell-wall metabolism or biofilm formation. Thus, it is essential to know how the expression and production of flotillins is controlled to establish new strategies to disrupt FMM-associated processes and to combat invasive hard-to-treat infections caused by human pathogens as Staphylococcus aureus. In this work we have found that the levels of FloA, the flotillin protein of S. aureus, are altered in the absence of the staphylococcal accessory regulator SarA, a staphylococcal-exclusive transcription factor involved in the regulation of virulence, antibiotic resistance and biofilm formation. FloA protein levels are post-transcriptionally regulated in the absence of SarA from the stationary phase of growth through their degradation by the intracellular ClpCP proteolytic complexes. The FloA degradation mechanism requires also the activity of the kinase McsB, probably by inducing the expression of clpC and clpP genes and not by acting as an adaptor protein tagging FloA for its ClpCP-dependent cleavage. The upregulation of protein quality control systems in the ΔsarA mutant is comparable to the unfolded protein response that occurs in mitochondria and Gram-negative bacteria to combat proteotoxic stress. We hypothesize that, in the absence of SarA, FloA is going to be misfolded/damaged in the transition to the stationary phase, probably due defects in molecular chaperones, triggering then its ClpCP-dependent cleavage. Therefore, the mechanism of regulation of FloA homeostasis by SarA involving the proteolytic complexes ClpCP and the kinase McsB described in this work introduces a new approach to disrupt FMM architecture and, thus combat hard-to-treat staphylococcal infections