Characterization of the Staphylococcus aureus Immunodominant Surface Antigen B, IsaB

• Main Author: Lawrence, Nicole
• Format: Others
• Published: VCU Scholars Compass 2010
• Subjects: Staphylococcus; virulence; Medicine and Health Sciences
• Online Access: http://scholarscompass.vcu.edu/etd/67; http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=1066&context=etd

Staphylococcus aureus is a significant cause of morbidity and mortality world-wide. This opportunistic pathogen is capable of causing several severe diseases that are exacerbated by its diverse and widespread antibiotic resistance profile. Therefore it is necessary to identify novel therapeutic targets to effectively treat S. aureus disease. Lorenz et al first described the Immunodominant Surface Antigen B, IsaB, because it was 1 of 4 unique proteins immunogenic during septicemia and not colonization, suggesting that IsaB may be a virulence factor and a possible novel therapeutic target. Interestingly, IsaB has no homology to proteins of known function and appears to be found only in Staphylococci. We sought to characterize the function of IsaB in S. aureus. We began our studies by determining how isaB was regulated by known S. aureus regulators and environmental stimuli. It was observed that the transcriptional regulator SarA represses expression of isaB, while serum and acidic pH induce expression. We found that IsaB is an extracellular nucleic acid binding protein, able to bind to dsDNA, ssDNA, and RNA and leads significant accumulation of eDNA on the cell surface. We employed multiple virulence models to ascertain the role of IsaB in virulence. Excitingly, we found that IsaB significantly protects S. aureus from antimicrobial peptides and Neutrophil Extracellular Traps, both components of the innate immune system. Another virulence mechanism of S. aureus is the ability to form biofilms. While recent studies show a significant role for eDNA in S. aureus biofilms, we found that IsaB actually had a negative affect on biofilms under certain growth conditions. Finally, to group IsaB into a known functional class, we successfully expressed and purified mature IsaB for structural determination by Nuclear Magnetic Resonance, which is currently underway. Our studies show that IsaB is a novel virulence factor of S. aureus, able to bind eDNA and significantly protect from AMPs and NETs, and could therefore play a key role in immune evasion.