Structural Insights into SraP-Mediated Staphylococcus aureus Adhesion to Host Cells

Abstract

Staphylococcus aureus, a Gram-positive bacterium causes a number of devastating human diseases, such as infective endocarditis, osteomyelitis, septic arthritis and sepsis. S. aureus SraP, a surface-exposed serine-rich repeat glycoprotein (SRRP), is required for the pathogenesis of human infective endocarditis via its ligand-binding region (BR) adhering to human platelets. It remains unclear how SraP interacts with human host. Here we report the 2.05 Å crystal structure of the BR of SraP, revealing an extended rod-like architecture of four discrete modules. The N-terminal legume lectin-like module specifically binds to N-acetylneuraminic acid. The second module adopts a β-grasp fold similar to Ig-binding proteins, whereas the last two tandem repetitive modules resemble eukaryotic cadherins but differ in calcium coordination pattern. Under the conditions tested, small-angle X-ray scattering and molecular dynamic simulation indicated that the three C-terminal modules function as a relatively rigid stem to extend the N-terminal lectin module outwards. Structure-guided mutagenesis analyses, in addition to a recently identified trisaccharide ligand of SraP, enabled us to elucidate that SraP binding to sialylated receptors promotes S. aureus adhesion to and invasion into host epithelial cells. Our findings have thus provided novel structural and functional insights into the SraP-mediated host-pathogen interaction of S. aureus.

Streptococcus oralis Neuraminidase Modulates Adherence to Multiple Carbohydrates on Platelets

“…This is a family of glycosylated surface proteins expressed by many Gram-positive organisms. Many of these proteins are known to play roles in attachment to a variety of host and bacterial surfaces and in biofilm formation (15,17,18,21,(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50). The S. oralis SRRP is encoded within a typical locus for this protein family, which includes genes predicted to encode proteins for glycosylation and secretion of the SRRP (47) (Fig.…”

“…SRRPs contain two glycosylated serine-rich repeat (SRR) regions which comprise the majority of the protein, a cell wall anchor, and one or two nonrepeat regions within the N-terminal region (16,52). The nonrepeat regions of SRRPs mediate adherence, and diversity in the modular structure of these regions accounts for the different receptors for these proteins, including sialic acid, keratins, and fibrinogen (16,20,23,35,40,44,45,51,(54)(55)(56). BLAST searches identified no significant sequence similarity between the nonrepeat region of S. oralis SRRP and other available sequences.…”

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

“…A sraP mutant was reported to have decreased biofilm formation, and SraP bound to S. aureus whole cell lysates, suggesting that SraP may self-associate or bind other targets on neighboring S. aureus cells to promote biofilm development (148). The ligand binding domain was recently structurally characterized and found to contain a lectin-like module that binds N-acetylneuraminic acid (149), an abundant sugar on host glycosylated proteins. The S. haemolyticus serine-rich repeat protein UafB mediates binding to fibronectin, fibrinogen, and human uroepithelial cells (150).…”

Molecular interactions and inhibition of the staphylococcal biofilm-forming protein SdrC

“…Although the polycationic polysaccharide intercellular adhesin has long been thought to be the main component promoting intercellular adhesion (4,5), there is now a compelling body of evidence that cell wall-anchored (CWA) proteins are also involved (2,3). Several recombinant CWA proteins have been shown to form dimers in solution (6)(7)(8)(9). In some cases (i.e., Aap), crystallographic studies have provided insights into the mechanism of dimer formation (9,10).…”

“…Several recombinant CWA proteins have been shown to form dimers in solution (6)(7)(8)(9). In some cases (i.e., Aap), crystallographic studies have provided insights into the mechanism of dimer formation (9,10). Although very useful, in vitro methods provide information on purified molecules that are removed from their cellular context.…”