Equilibrium of sortase A dimerization on Staphylococcus aureus cell surface mediates its cell wall sorting activity

Area of Science:

• Microbiology
• Enzymology
• Cell Biology

Background:

• Staphylococcus aureus sortase A (SrtA) is a transpeptidase enzyme crucial for Gram-positive bacteria.
• SrtA anchors cell surface proteins to the peptidoglycan layer, influencing bacterial adhesion and virulence.
• The oligomeric state of SrtA and its functional implications on the cell membrane remain largely unexplored.

Purpose of the Study:

• To investigate the homo-dimerization of SrtA on the bacterial cell membrane.
• To determine the functional significance of SrtA dimerization on enzyme activity and bacterial virulence.
• To compare the cell surface protein display and host cell invasion efficiency of wild-type SrtA and a monomeric SrtA mutant.

Main Methods:

• Direct observation of SrtA homo-dimerization on the bacterial cell membrane.
• Site-directed mutagenesis to create a monomeric SrtA mutant.
• Quantification of cell surface adhesive protein display.
• Cell-based invasion assays to assess host cell entry efficiency.

Main Results:

• SrtA was directly observed to undergo highly selective homo-dimerization on the cell membrane.
• A monomeric SrtA mutant exhibited more prominent cell surface display of adhesive proteins compared to wild-type SrtA.
• Bacteria expressing the monomeric SrtA mutant demonstrated significantly higher efficiency in invading host mammalian cells.

Conclusions:

• The monomeric form of SrtA appears to be more active in displaying virulence factors on the cell surface than the dimeric form.
• SrtA dimerization influences bacterial pathogenesis, with the monomeric state potentially enhancing infectivity.
• Understanding SrtA oligomerization provides insights into its catalytic mechanism and offers potential targets for novel anti-infective agents.