Staphylococcal SplA and SplB serine proteases target ubiquitin(-like) specific proteases

Area of Science:

• Microbiology
• Biochemistry
• Immunology

Background:

• Staphylococcus aureus is a common human pathogen causing severe infections.
• Extracellular serine protease-like proteins (Spls) are virulence factors of S. aureus with unknown functions.
• Understanding Spl substrates is crucial for elucidating their role in infection.

Purpose of the Study:

• To characterize the substrate and cleavage specificity of SplA and SplB.
• To identify novel pathophysiological substrates of S. aureus Spls.
• To investigate the role of Spls in manipulating host immune responses.

Main Methods:

• Recombinant expression and purification of SplA and SplB proteins.
• Mass spectrometry-based substrate identification and cleavage site mapping.
• Site-directed mutagenesis to confirm cleavage sites in target proteins.

Main Results:

• Identified ubiquitin or ubiquitin-like modifying enzymes as novel substrates for SplA and SplB.
• Determined distinct cleavage sites for SplA (YLY↓T, FMY↓N) and SplB (VCD↓S).
• Demonstrated that Spls cleave key components of ubiquitination pathways.

Conclusions:

• SplA and SplB specifically cleave ubiquitin-modifying enzymes, including deubiquitinating enzymes.
• This cleavage activity suggests a mechanism for S. aureus to manipulate host immune signaling.
• Spls may play a role in bacterial competition and pathogenesis by targeting immune pathways.