Mechanistic basis of staphylococcal interspecies competition for skin colonization

Abstract

Staphylococci, whether beneficial commensals or pathogens, often colonize human skin, potentially leading to competition for the same niche. In this multidisciplinary study we investigate the structure, binding specificity, and mechanism of adhesion of the Aap lectin domain required forStaphylococcus epidermidisskin colonization and compare its characteristics to the lectin domain from the orthologousStaphylococcus aureusadhesin SasG. The Aap structure reveals a legume lectin-like fold with atypical architecture, showing specificity for N-acetyllactosamine and sialyllactosamine. Bacterial adhesion assays using human corneocytes confirmed the biological relevance of these Aap-glycan interactions. Single-cell force spectroscopy experiments measured individual binding events between Aap and corneocytes, revealing an extraordinarily tight adhesion force of nearly 900 nN and a high density of receptors at the corneocyte surface. The SasG lectin domain shares similar structural features, glycan specificity, and corneocyte adhesion behavior. We observe cross-inhibition of Aap- and SasG-mediated staphylococcal adhesion to corneocytes. Together, these data provide insights into staphylococcal interspecies competition for skin colonization and suggest potential avenues for inhibition ofS. aureuscolonization.

Staphylococcus aureusskin colonization is mediated by SasG lectin variation

“…Both the Aap and SasG-I lectins have a key active site aromatic residue that has been linked to glycan binding and corneocyte adhesion, which is Y580 in Aap and W392 in SasG-I 16 . Based on an alignment of the SasG-I and SasG-II lectins, this aromatic residue is missing in SasG-II and is replaced with non-aromatics ( Fig.…”

“…Other secondary structure elements are similar, as expected given that both adopt β-sandwich L-type lectin folds. Based on our previous analysis of the SasG-I and Aap lectin structures 16 , most of the key residues in the vicinity of the glycan binding site (shortly after β17) are conserved between SasG-I and SasG-II, with one important exception, as described below.…”

“…SasG is a large sortase-anchored protein that is part of the G5-E repeat family of adhesins 11 . The structure of this protein consists of a N-terminal A domain encompassing an intrinsically disordered region and L-type lectin, a B domain with highly-conserved, serial B-repeats containing G5-repeat and E-spacer sub-domains 11,16,18 , and a proline/glycine-rich stalk region extending to the C-terminus 20 . SasG is orthologous to accumulation-associated protein (Aap) in S. epidermidis , and SasG homologs are expressed in other species of staphylococci as well 15 .…”

“…Furthermore, Maciag et al identified key aromatic residues within the glycan-binding pockets of the Aap and SasG lectins, which likely bind glycans through stacking interactions. These key aromatic residues are approximately in the same structural position, Y580 for Aap and W392 for SasG, and mutation of these residues to alanine abrogated binding of these lectins to N-acetyl-D-lactosamine and 3’-sialyl-N-acetyllactosamine as determined via isothermal titration calorimetry (ITC) 16 . Similarly, pre-incubating corneocytes from healthy human skin with purified lectins from Aap and SasG significantly reduced adhesion of both S. epidermidis and S. aureus , while the mutated lectins did not affect adhesion 16 , demonstrating that Aap and SasG bind to the ligand via these key residues in the lectin subdomain.…”

Skin Microbiota and the Skin Barrier

“…S. epidermidis –derived δ-toxin cooperates with host-derived AMPs, such as LL-37, cathelicidin-related AMP, hBD2, and hBD3, and interacts with neutrophil extracellular traps against group A Streptococcus . 25 Certain CoNS like Staphylococcus caprae antagonize S. aureus by secreting autoinducing peptides, counteracting S. aureus PSM-α peptides that directly act on human keratinocytes and break down the epidermal barrier and interfere with the accessory gene regulator quorum-sensing system of S. aureus . 11 Cutibacterium species are the most prevalent and abundant organisms in human skin sebaceous follicles, and cutimycin-producing strains selectively inhibit S. aureus colonization via pilosebaceous niche competition.…”