Identification of a Staphylococcus aureus extracellular matrix-binding protein with broad specificity

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Staphylococcus aureus is a significant human pathogen.
• Extracellular matrix glycoproteins play crucial roles in bacterial adhesion and pathogenesis.
• Identifying bacterial receptors for these glycoproteins is key to understanding host-pathogen interactions.

Purpose of the Study:

• To identify and characterize Staphylococcus aureus surface proteins that bind bone sialoprotein (BSP).
• To investigate the binding specificities of these identified proteins.
• To explore the potential role of these proteins as receptors for extracellular matrix glycoproteins.

Main Methods:

• Solubilization and separation of staphylococcal proteins using SDS-PAGE.
• Probing blotted proteins with radiolabeled bone sialoprotein (125I-BSP).
• Purification of binding proteins via LiCl extraction and cation-exchange chromatography.
• Western ligand blotting to determine binding specificities.
• Hemagglutination assays to assess the function of the 60-kDa protein.

Main Results:

• Several staphylococcal strains possess surface proteins that bind BSP.
• Major BSP-binding proteins with apparent molecular masses of 72 kDa and 60 kDa were identified.
• The 72-kDa protein demonstrated broad binding specificity, interacting with BSP, fibronectin, fibrinogen, vitronectin, thrombospondin, and collagen.
• The 60-kDa protein exhibited hemagglutination activity and its binding activity was influenced by specific carbohydrates.
• Protein expression levels correlated with BSP binding capacity.

Conclusions:

• Purified 72-kDa and 60-kDa proteins from Staphylococcus aureus act as receptors for extracellular matrix glycoproteins.
• These proteins exhibit broad specificity, suggesting a significant role in bacterial adhesion and colonization.
• The 60-kDa protein may function as a carbohydrate-binding protein involved in bacterial interactions.