Regulation of Host Hemoglobin Binding by the Staphylococcus aureus Clp Proteolytic System

Abstract

Protein turnover is a key process for bacterial survival mediated by intracellular proteases. Proteolytic degradation reduces the levels of unfolded and misfolded peptides that accumulate in the cell during stress conditions. Three intracellular proteases, ClpP, HslV, and FtsH, have been identified in the Gram-positive bacterium Staphylococcus aureus, a pathogen responsible for significant morbidity and mortality worldwide. Consistent with their crucial role in protein turnover, ClpP, HslV, and FtsH affect a number of cellular processes, including metabolism, stress responses, and virulence. The ClpP protease is believed to be the principal degradation machinery in S. aureus. This study sought to identify the effect of the Clp protease on the iron-regulated surface determinant (Isd) system, which extracts heme-iron from host hemoglobin during infection and is critical to S. aureus pathogenesis. Inactivation of components of the Clp protease alters abundance of several Isd proteins, including the hemoglobin receptor IsdB. Furthermore, the observed changes in IsdB abundance are the result of transcriptional regulation, since transcription of isdB is decreased by clpP or clpX inactivation. In contrast, inactivation of clpC enhances isdB transcription and protein abundance. Loss of clpP or clpX impairs host hemoglobin binding and utilization and results in severe virulence defects in a systemic mouse model of infection. These findings suggest that the Clp proteolytic system is important for regulating nutrient iron acquisition in S. aureus. The Clp protease and Isd complex are widely conserved in bacteria; therefore, these data reveal a novel Clp-dependent regulation pathway that may be present in other bacterial pathogens.

Stepwise Decrease in Daptomycin Susceptibility in Clinical Staphylococcus aureus Isolates Associated with an Initial Mutation in rpoB and a Compensatory Inactivation of the clpX Gene

“…The underlying mechanism remains unclear but will be the subject of further studies. The in vivo selection of a mutation that abolished the synthesis of the ClpX chaperone was surprising, as ClpX is required for the virulence of S. aureus in animal models of infection (22,23). The severely decreased virulence of the clpX mutant has been attributed to the reduced expression of a number of major virulence factors, including hemolysins and protein A (22,24,25).…”

“…The highly conserved ClpX chaperone has a dual role in the cell; it targets proteins for degradation by associating with the ClpP peptidase, and, independently of ClpP, it facilitates protein folding and interactions (21). Interestingly, inactivation of clpX severely reduced the virulence of S. aureus in both localized and systemic models of infection, suggesting that ClpX is indispensable for S. aureus during infection (22,23). Consistent with this finding, the clpX mutant expresses substantially reduced amounts of important virulence factors, such as hemolysins and protein A (22,24,25).…”

An Iron-Regulated Autolysin Remodels the Cell Wall To Facilitate Heme Acquisition in Staphylococcus lugdunensis

“…Tryptic soy broth (TSB) (Difco) was used as an iron-rich medium. Iron-restricted media were generated by adding the iron chelator 2,2-dipyridyl (DIP) (31). In short, overnight cultures of S. lugdunensis strains were subcultured (1:100) into TSB alone or with 350 M DIP.…”

Effects of Alterations in Staphylococcus aureus Cell Membrane and Cell Wall in Antimicrobial Resistance

“…In various pathogenic microorganisms, such as Listeria monocytogenes, Streptococcus pneumoniae and S. aureus, ClpP proteases have been identiied in in vivo expression studies as an important virulence factor [44,48,49]. Knockout studies of the clpP ATP-dependent gene in S. aureus, followed by global transcriptional analysis using DNA microarray technology, showed that the loss of clpP leads to complete derepression of transcription of the CtsR gene (or yacG, a polypeptide transcriptional regulator).…”

“…ClpP plays an essential role in the degradation of pathogen cell wall but also in the regulation of their virulence [44]. The ClpP components in S. aureus are responsible for initiating physiological adaptive responses against diferent external pressures, including extreme changes in temperature, osmolarity and oxidative stress [45].…”