Clusterin, a putative complement regulator, binds to the cell surface of Staphylococcus aureus clinical isolates

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Staphylococcus aureus is a significant human pathogen.
• Clusterin is a human glycoprotein involved in various biological processes, including immune regulation.
• The interaction between S. aureus and clusterin is not well understood.

Purpose of the Study:

• To investigate the binding of clusterin to Staphylococcus aureus.
• To characterize the nature of this interaction and identify potential bacterial receptors.
• To explore the implications of clusterin binding for S. aureus virulence.

Main Methods:

• Enzyme-linked immunosorbent assay (ELISA) and flow cytometry were used to detect clusterin binding.
• Saturation binding studies were performed to determine binding affinity.
• Protease treatment was used to assess the proteinaceous nature of the binding sites.

Main Results:

• All tested S. aureus strains, including clinical isolates, bound to clusterin.
• Nonpathogenic bacteria (Bacillus subtilis, Escherichia coli) did not bind clusterin.
• Clusterin binding to S. aureus was saturable, inhibited by excess unlabeled clusterin, and prevented by protease treatment, with affinity constants ranging from 31 to 57 nM.
• Clusterin induced aggregation of S. aureus cells but not control bacteria.

Conclusions:

• Staphylococcus aureus possesses specific proteinaceous receptors for clusterin.
• These receptors may represent a novel bacterial virulence factor for S. aureus.
• Clusterin binding could influence S. aureus pathogenesis, possibly by modulating complement activity.