The Staphylococcus aureus surface protein SasG and its homologues promote bacterial adherence to human desquamated nasal epithelial cells

Abstract

Staphylococcus aureus binds to human desquamated nasal epithelial cells, a phenomenon likely to be important in nasal colonization. ClfB was identified previously as one staphylococcal adhesin that promoted binding to nasal epithelia. In this study, it is shown that the S. aureus surface protein SasG, identified previously by in silico analysis of genome sequences, and two homologous proteins, Pls of S. aureus and AAP of Staphylococcus epidermidis, also promote bacterial adherence to nasal epithelial cells. Conditions for in vitro expression of SasG by S. aureus were not found. Adherence assays were therefore performed with S. aureus and Lactococcus lactis expressing SasG from an expression plasmid. These studies showed that SasG did not bind several ligands typically bound by S. aureus. Significantly, SasG and Pls did promote bacterial adherence to nasal epithelial cells. Furthermore, pre-incubation of epithelial cells with purified recombinant proteins revealed that the N-terminal A regions of SasG, Pls and AAP, but not the B repeats of SasG, inhibited adherence of L. lactis expressing SasG in a dose-dependent fashion. These results suggest that SasG, Pls and AAP bind to the same as-yet-unidentified receptor on the surface of nasal epithelial cells. In addition, expression of SasG, like Pls, reduced adherence of S. aureus to fibronectin and fibrinogen.

Characterization of a Strain of Community-AssociatedMethicillin-Resistant Staphylococcus aureus WidelyDisseminated in the UnitedStates

“…Likewise, the extracellular matrix-binding protein homologue, ebh (which is represented by several oligonucleotides on the microarray), and fnbA and fnbB (14, 32) (which encode fibronectin-binding protein) were present. All isolates tested also harbored the genes encoding eight LPXTG-containing proteins, protein A (spa), the elastin-binding protein (ebpS) (56), accumulation-associated protein (sasG) (60), and the intercellular adhesin (icaA to icaD) (16).…”

Staphylococcal biofilm-forming protein has a contiguous rod-like structure

“…Aap and SasG have a domain organization that is typical of the LPXTG protein family, comprising an N-terminal secretion signal and a C-terminal sorting peptide, which is essential for covalent linkage to wall peptidoglycan (10) (Fig. 1A).…”

“…They contain an N-terminal A domain, followed by a stretch of tandemly arrayed "B" repeats. The A domains of SasG and Aap have been implicated in adhesion of bacteria to desquamated epithelial cells (10) and B repeat regions are responsible for cellto-cell accumulation during biofilm formation (11,12). Although annotations in the literature differ (13,14), the Pfam database (15) recognizes a B-repeat sequence as containing a G5 domain (∼80 residues) (14) followed by an approximately 50-residue sequence (herein called E; Fig.…”

Methicillin-resistant Staphylococcus aureus antibiotic resistance and virulence

“…Clumping factor B and Staphylococcus aureus surface proteins G and X (SasG, SasX) have been shown to combine to nasal epithelial cells (58)(59)(60). Among them, SasX lately has attracted more attention because it was found to play an important role in an MRSA epidemic (60).…”