Functional characteristics of the Staphylococcus aureus δ-toxin allelic variant G10S

Impact of Missense Variants on the Structure and Function of Polycystic Ovary Syndrome-Associated HSD17B1 Gene

HSD17B1 regulates estrogen availability in the ovary, and its dysregulation is linked to cyst formation in polycystic ovary syndrome. This study aimed to understand the role of missense variants in HSD17B1 dysfunction. Bioinformatic tools (sift, polyphen2, panther, snps & go, phd-snp, pmut, snap and revel score) were used to identify the deleterious missense variants of HSD17B1 gene. InterPro and Pfam tools were utilized to predict the functional domain of these deleterious variants, and its impact on structure and stability of HSD17B1 was analyzed by Hope, MutPred2, I-Mutant 2.0, and Mupro. Further, the AutoDock was used to determine the binding affinity of NADP to HSD17B1 protein. Finally, the HSD17B1 expression in clinical samples was analyzed using qRT-PCR. Of the 355 missense variants identified, five (rs202173252, rs149630844, rs146159533, rs200202791, and rs138503851) variants were deleterious, pocketed at the NADP binding domain and located at the conserved region of HSD17B1. Further, series of in silico prediction and molecular docking shows only the variant T191I (rs138503851) has an adverse effect on HSD17B1 function because of increased unfavorable bonds and non-interaction of adenine and nicotinamide of NADP to the Glycine94 and Leucine93 of HSD17B1. Additionally, a two-fold reduced expression of HSD17B1 in peripheral blood of PCOS subjects was observed, compared to healthy individuals. Overall, these results indicate that rs138503851 genetic variant of HSD17B1 may affect estrogen synthesis in PCOS. However, further clinical studies are warranted to validate the presence of rs138503851 genetic variant to identify the potential females who are predisposal to the development of PCOS.

The multifaceted helical net of amphipathic alpha-helices; the next dimension of the helical peptide wheel

The amphipathic nature of helical proteins is crucial to their binding features across a broad spectrum of physiological examples, including heat-shock proteins and hyaluronic acid (HA) receptor binding. By taking advantage of the amphipathic balance of amino acids and their presentation in helical faces, novel synthetic peptides can be designed to improve biofunctionality. We present a new approach for designing synthetic alpha helical peptides using a multifaceted analysis, which allows for new bioengineering designs of amphipathic alpha helices. Amphipathic helical peptides were presented with distinct hydrophobic and hydrophilic faces; two series of analogs, namely, peptides AX9 and AX7, were designed to contain a hydrophobic and hydrophilic face, respectively. The presence of one series of peptides exhibited a distinct hydrophobic face and the second series exhibited a distinct hydrophilic face, which was corroborated with reversed-phase chromatography (C8). Using a multifaceted approach to analyze the potential faces of an amphipathic helix, we demonstrated that these helices contain seven distinct "side-viewed" helical faces (based on the hydrophobic face of the AXP series of analogs), which provides additional spatial dimensional information beyond the averaging effect of the hydrophobic moment generated from the "top-down" view of a helical wheel. Furthermore, we cross-compared our recently published HA-binding peptide in this manner to demonstrate that the most significant binding was related to (1) balanced amphipathicity and (2) a distribution of the key HA-binding domain B1(X7)B2 presented spatially. For example, our most effective peptide binder 17x-3 has five of seven faces with B1(X7)B2 domains, while the positive control mPEP35 has three, which reflects a lower affinity. With such a tool, one is able to map helical peptides on an additional dimension to characterize and redesign fundamental amphipathic properties among other critical characteristics, such as sugar and glycan binding, which is a fundamental characteristic feature of cellular interactions in almost every biological system.

Contribution of staphylococcal virulence factors in the pathogenesis of thrombosis

Staphylococci are responsible for many infections in humans, starting with skin and soft tissue infections and finishing with invasive diseases such as endocarditis, sepsis and pneumonia, which lead to high mortality. Patients with sepsis often demonstrate activated clotting pathways, decreased levels of anticoagulants, decreased fibrinolysis, activated endothelial surfaces and activated platelets. This results in disseminated intravascular coagulation and formation of a microthrombus, which can lead to a multiorgan failure. This review describes various staphylococcal virulence factors that contribute to vascular thrombosis, including deep vein thrombosis in infected patients. The article presents mechanisms of action of different factors released by bacteria in various host defense lines, which in turn can lead to formation of blood clots in the vessels.

Lipase-mediated detoxification of host-derived antimicrobial fatty acids by Staphylococcus aureus

Long-chain fatty acids with antimicrobial properties are abundant on the skin and mucosal surfaces, where they are essential to restrict the proliferation of opportunistic pathogens such as Staphylococcus aureus. These antimicrobial fatty acids (AFAs) elicit bacterial adaptation strategies, which have yet to be fully elucidated. Characterizing the pervasive mechanisms used by S. aureus to resist AFAs could open new avenues to prevent pathogen colonization. Here, we identify the S. aureus lipase Lip2 as a novel resistance factor against AFAs. Lip2 detoxifies AFAs via esterification with cholesterol. This is reminiscent of the activity of the fatty acid-modifying enzyme (FAME), whose identity has remained elusive for over three decades. In vitro, Lip2-dependent AFA-detoxification was apparent during planktonic growth and biofilm formation. Our genomic analysis revealed that prophage-mediated inactivation of Lip2 was rare in blood, nose, and skin strains, suggesting a particularly important role of Lip2 for host - microbe interactions. In a mouse model of S. aureus skin colonization, bacteria were protected from sapienic acid (a human-specific AFA) in a cholesterol- and lipase-dependent manner. These results suggest Lip2 is the long-sought FAME that exquisitely manipulates environmental lipids to promote bacterial growth in otherwise inhospitable niches.

β-Hemolysin, not agrA mutation, inhibits the hemolysis of α-hemolysin in Staphylococcus aureus laboratory and clinical strains

Staphylococcus aureus produces various hemolysins regulated by the Agr-QS system, except β-hemolysin encoded by the gene hlb. A classical laboratory S. aureus strain RN4220 displays only the β-hemolysin phenotype. It was suspected that the 8A mutation at the end of its agrA gene delayed the expressions of hla and RNAIII, then failed to express α- and δ-hemolysins. However, hla gene expression was detected at the later culture time without α-hemolysin phenotype, the reason for such a phenotype has not been clearly understood. We created hlb knockout and complementary mutants via homologous recombination in RN4220 and NRS049, two strains that normally produce β-hemolysin and carry agrA mutation. We found interestingly that the presence or absence of α-hemolysin phenotype in such strains depended on the expression of β-hemolysin instead of agrA mutations, which only inhibited δ-hemolysin expression. The hemolysis phenotype was verified by the Christie-Atkinson-Munch-Peterson (CAMP) test. Quantitative reverse transcription PCR was carried out to evaluate the relative gene expressions of hlb, hla, and RNAIII. The construction of mutants did not affect the agrA mutation status. We demonstrate that the absence of α-hemolysin in S. aureus RN4220 and NRS049 strains is attributed to their production of β-hemolysin instead of agrA mutation. Our findings broaden the understanding of the molecular mechanisms that control hemolysin expression in S. aureus that is crucial for the development of new therapeutic strategies to combat S. aureus infections.

IMPORTANCE

α-Hemolysin is a critical virulence factor in Staphylococcus aureus and its expression is largely controlled by the Agr-QS system. Nonetheless, the hemolysis phenotype and the regulation of the Agr-QS system in S. aureus still hold many mysteries. Our study finds that it is the expression of β- hemolysin rather than the agrA mutation that inhibits the function of the α-hemolysin in an important S. aureus strain RN4220 and a clinical strain presents a similar phenotype, which clarifies the misunderstood hemolytic phenotype and mechanism of S. aureus. Our findings highlight the interactions among different toxins and their biological roles, combined with QS system regulation, which is ultimately the true underlying cause of its virulence. This emphasizes the importance of considering the collaborative action of various factors in the infection process caused by this significant human pathogen.

Virulence attributes of successful methicillin-resistant Staphylococcus aureus lineages

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of severe and often fatal infections. MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage. Selection pressures in both hospital and community settings are not uniform across the globe, which has resulted in geographically distinct epidemiology. This review focuses on the mechanisms that trigger the establishment and maintenance of current, dominant MRSA lineages across the globe. While the important role of antibiotic resistance will be mentioned throughout, factors which influence the capacity of S. aureus to colonize and cause disease within a host will be the primary focus of this review. We show that while MRSA possesses a diverse arsenal of toxins including alpha-toxin, the success of a lineage involves more than just producing toxins that damage the host. Success is often attributed to the acquisition or loss of genetic elements involved in colonization and niche adaptation such as the arginine catabolic mobile element, as well as the activity of regulatory systems, and shift metabolism accordingly (e.g., the accessory genome regulator, agr). Understanding exactly how specific MRSA clones cause prolonged epidemics may reveal targets for therapies, whereby both core (e.g., the alpha toxin) and acquired virulence factors (e.g., the Panton-Valentine leukocidin) may be nullified using anti-virulence strategies.

New insight into the virulence and inflammatory response of Staphylococcus aureus strains isolated from diabetic foot ulcers

Staphylococcus aureus strains isolated from diabetic foot ulcers (DFUs) have less virulence, but still cause severe infections. Furthermore, hypovirulent S. aureus strains appear to be localized in the deep tissues of diabetic foot osteomyelitis, indicating that the unique environment within DFUs affects the pathogenicity of S. aureus. In this study, the cell-free culture medium (CFCM) of S. aureus strains isolated from DFUs exhibited higher cytotoxicity to human erythrocytes than those isolated from non-diabetic patients with sepsis or wounds. Among these S. aureus strains isolated from DFUs, β-toxin negative strains have less virulence than β-toxin positive strains, but induced a higher expression of inflammatory cytokines. Our study and previous studies have shown that the synergistic effect of phenol-soluble modulin α and β-toxin contributes to the higher hemolytic activity of β-toxin positive strains. However, lysis of human erythrocytes by the CFCM of β-toxin negative strains was greatly inhibited by an autolysin inhibitor, sodium polyanethole sulfonate (SPS). A high level of glucose greatly reduced the hemolytic activity of S. aureus, but promoted the expression of interleukin-6 (IL-6) in human neutrophils. However, 5 mM glucose or glucose-6-phosphate (G6P) increased the hemolytic activity of SA118 (a β-toxin negative strain) isolated from DFUs. Additionally, patients with DFUs with growth of S. aureus had lower level of serum IL-6 than those with other bacteria, and the CFCM of S. aureus strains significantly reduced lipopolysaccharide-induced IL-6 expression in human neutrophils. Therefore, the virulence and inflammatory response of S. aureus strains isolated from DFUs are determined by the levels of glucose and its metabolites, which may explain why it is the predominant bacteria isolated from DFUs.

Leaky barriers to gene sharing between locally co-existing coagulase-negative Staphylococcus species

Coagulase-negative Staphylococcus (CoNS) are opportunistic pathogens implicated in many human and animal infections. The evolutionary history of CoNS remains obscure because of the historical lack of recognition for their clinical importance and poor taxonomic sampling. Here, we sequenced the genomes of 191 CoNS isolates representing 15 species sampled from diseased animals diagnosed in a veterinary diagnostic laboratory. We found that CoNS are important reservoirs of diverse phages, plasmids and mobilizable genes encoding antimicrobial resistance, heavy metal resistance, and virulence. Frequent exchange of DNA between certain donor-recipient partners suggests that specific lineages act as hubs of gene sharing. We also detected frequent recombination between CoNS regardless of their animal host species, indicating that ecological barriers to horizontal gene transfer can be surmounted in co-circulating lineages. Our findings reveal frequent but structured patterns of transfer that exist within and between CoNS species, which are driven by their overlapping ecology and geographical proximity.

Bioinformatics study of expression from genomes of epidemiologically related MRSA CC398 isolates from human and wild animal samples

One of the most important livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) genetic lineages is the clonal complex (CC) 398, which can cause typical S. aureus-associated infections in people. In this work, whole-genome sequencing, RNA-sequencing, and gel-based comparative proteomics were applied to study the genetic characteristics of three MRSA CC398 isolates recovered from humans (strains C5621 and C9017), and from an animal (strain OR418). Of the three strains, C9017 presented the broadest resistance genotype, including resistance to fluroquinolone, clindamycin, tiamulin, macrolide and aminoglycoside antimicrobial classes. The scn, sak, and chp genes of the immune evasion cluster system were solely detected in OR418. Pangenome analysis showed a total of 288 strain-specific genes, most of which are hypothetical or phage-related proteins. OR418 had the most pronounced genetic differences. RNAIII (δ-hemolysin) gene was clearly the most expressed gene in OR418 and C5621, but it was not detected in C9017. Significant differences in the proteome profiles were found between strains. For example, the immunoglobulin-binding protein Sbi was more abundant in OR418. Considering that Sbi is a multifunctional immune evasion factor in S. aureus, the results point to OR418 strain having high zoonotic potential. Overall, multiomics biomarker signatures can assume an important role to advance precision medicine in the years to come. SIGNIFICANCE: MRSA is one of the most representative drug-resistant pathogens and its dissemination is increasing due to MRSA capability of establishing new reservoirs. LA-MRSA is considered an emerging problem worldwide and CC398 is one of the most important genetic lineages. In this study, three MRSA CC398 isolates recovered from humans and from a wild animal were analyzed through whole-genome sequencing, RNA-sequencing, and gel-based comparative proteomics in order to gather systems-wide omics data and better understand the genetic characteristics of this lineage to identify distinctive markers and genomic features of relevance to public health. The scn, sak, and chp genes of the immune evasion cluster system were solely detected in OR418. Pangenome analysis showed a total of 288 strain-specific genes, most of which are hypothetical or phage-related proteins. OR418 had the most pronounced genetic differences. RNAIII (δ-hemolysin) gene was clearly the most expressed gene in OR418 and C5621, but it was not detected in C9017. Significant differences in the proteome profiles were found between strains.

Genotypes of Staphylococcus aureus Clinical Isolates Are Associated with Phenol-Soluble Modulin (PSM) Production

Phenol-soluble modulins (PSMs) are important S. aureus virulence factors that cause cytolysis, mast cell degranulation, and stimulate inflammatory responses. In this study, PSM production by S. aureus clinical isolates was measured by liquid chromatography/mass spectrometry (LC-MS) and correlated with staphylococcal protein A (spa) type and staphylococcal cassette chromosome mec (SCCmec) type. Of 106 S. aureus clinical isolates, 50 (47.2%) corresponded to methicillin-susceptible S. aureus (MSSA) and 56 (52.8%) to methicillin-resistant S. aureus (MRSA). LC-MS analysis revealed no significant difference in average PSMα3, PSMα4, PSMβ2, and δ-toxin production between MSSA and MRSA isolates, but PSMα1, PSMα2, and PSMβ1 production were higher in MSSA than MRSA. This study demonstrated that average PSMα1–α4, PSMβ1–β2, and δ-toxin production by SCCmec type II strains was significantly lower than the IV, IVA, and V strains. Most of the SCCmec type II strains (n = 17/25; 68.0%) did not produce δ-toxin, suggesting a dysfunctional Agr system. The spa type t111 (except one strain) and t2460 (except one strain producing PSM α1–α4) did not produce PSMα1–α4 and δ-toxin, while average PSM production was higher among the t126 and t1784 strains. This study showed that the genotype of S. aureus, specifically the spa and SCCmec types, is important in characterizing the production of PSMs.

Identification of responsible amino acid residues in Staphylococcal superantigen-like 12 for the activation of mast cells

Staphylococcal superantigen-like 12 (SSL12) is reported to evoke the degranulation in murine mast cells. The allelic variant of SSL12 in the genome of reference strain NCTC8325 induced the degranulation of murine mast cells, that of MRSA252 strain did not, nevertheless relatively high sequence similarity (82%). To identify responsible amino acid residues of SSL12 for mast cell activation, we created a series of domain swap mutants and amino acid substitution mutants between the active and inactive variants. The mutants that harbored oligonucleotide/oligosaccharide binding (OB)-fold domain of the active variant activated mast cells. The replacement at position 56 (L56F) in the OB-fold domain diminished the mast cell stimulatory activity, and the combinatorial substitutions L56F/K92E, L56F/D95S, and L56F/S100V abolished the stimulatory activities of the mutant that harbored OB-fold domain of the active variant and the intact active variant. These indicate that the responsive elements of SSL12 for mast cell activation are in the OB-fold of SSL12, and L56 would be an essential amino acid residue for the activation of mast cells. The findings would contribute to the understanding of the molecular mechanism of SSL12 for mast cell activation and the development of toxoids preventing allergic inflammations associated with S. aureus. This article is protected by copyright. All rights reserved.

Staphylococcus aureus Depends on Eap Proteins for Preventing Degradation of Its Phenol-Soluble Modulin Toxins by Neutrophil Serine Proteases

Neutrophil granulocytes act as a first line of defense against pathogenic staphylococci. However, Staphylococcus aureus has a remarkable capacity to survive neutrophil killing, which distinguishes it from the less-pathogenic Staphylococcus epidermidis. Both species release phenol-soluble modulin (PSM) toxins, which activate the neutrophil formyl-peptide receptor 2 (FPR2) to promote neutrophil influx and phagocytosis, and which disrupt neutrophils or their phagosomal membranes at high concentrations. We show here that the neutrophil serine proteases (NSPs) neutrophil elastase, cathepsin G and proteinase 3, which are released into the extracellular space or the phagosome upon neutrophil FPR2 stimulation, effectively degrade PSMs thereby preventing their capacity to activate and destroy neutrophils. Notably, S. aureus, but not S. epidermidis, secretes potent NSP-inhibitory proteins, Eap, EapH1, EapH2, which prevented the degradation of PSMs by NSPs. Accordingly, a S. aureus mutant lacking all three NSP inhibitory proteins was less effective in activating and destroying neutrophils and it survived less well in the presence of neutrophils than the parental strain. We show that Eap proteins promote pathology via PSM-mediated FPR2 activation since murine intraperitoneal infection with the S. aureus parental but not with the NSP inhibitors mutant strain, led to a significantly higher bacterial load in the peritoneum and kidneys of mFpr2^-/- compared to wild-type mice. These data demonstrate that NSPs can very effectively detoxify some of the most potent staphylococcal toxins and that the prominent human pathogen S. aureus has developed efficient inhibitors to preserve PSM functions. Preventing PSM degradation during infection represents an important survival strategy to ensure FPR2 activation.

Signal inhibitory receptor on leukocytes-1 recognizes bacterial and endogenous amphipathic α-helical peptides

Signal inhibitory receptor on leukocytes-1 (SIRL-1) is a negative regulator of myeloid cell function and dampens antimicrobial responses. We here show that different species of the genus Staphylococcus secrete SIRL-1-engaging factors. By screening a library of single-gene transposon mutants in Staphylococcus aureus, we identified these factors as phenol-soluble modulins (PSMs). PSMs are amphipathic α-helical peptides involved in multiple aspects of staphylococcal virulence and physiology. They are cytotoxic and activate the chemotactic formyl peptide receptor 2 (FPR2) on immune cells. Human cathelicidin LL-37 is also an amphipathic α-helical peptide with antimicrobial and chemotactic activities, structurally and functionally similar to α-type PSMs. We demonstrate that α-type PSMs from multiple staphylococcal species as well as human cathelicidin LL-37 activate SIRL-1, suggesting that SIRL-1 recognizes α-helical peptides with an amphipathic arrangement of hydrophobicity, although we were not able to show direct binding to SIRL-1. Upon rational peptide design, we identified artificial peptides in which the capacity to ligate SIRL-1 is segregated from cytotoxic and FPR2-activating properties, allowing specific engagement of SIRL-1. In conclusion, we propose staphylococcal PSMs and human LL-37 as a potential new class of natural ligands for SIRL-1.

Direct identification of bacterial and human proteins from infected wounds in living 3D skin models

Trauma is one of the leading causes of death in people under the age of 49 and complications due to wound infection are the primary cause of death in the first few days after injury. The ESKAPE pathogens are a group of bacteria that are a leading cause of hospital-acquired infections and a major concern in terms of antibiotic resistance. Here, we demonstrate a novel and highly accurate approach for the rapid identification of ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) directly from infected wounds in 3D in vitro skin models. Wounded skin models were inoculated with bacteria and left to incubate. Bacterial proteins were identified within minutes, directly from the wound, by liquid extraction surface analysis mass spectrometry. This approach was able to distinguish closely related strains and, unlike genomic approaches, can be modified to provide dynamic information about pathogen behaviour at the wound site. In addition, since human skin proteins were also identified, this method offers the opportunity to analyse both host and pathogen biomarkers during wound infection in near real-time.

Integrated molecular imaging reveals tissue heterogeneity driving host-pathogen interactions

Diseases are characterized by distinct changes in tissue molecular distribution. Molecular analysis of intact tissues traditionally requires preexisting knowledge of, and reagents for, the targets of interest. Conversely, label-free discovery of disease-associated tissue analytes requires destructive processing for downstream identification platforms. Tissue-based analyses therefore sacrifice discovery to gain spatial distribution of known targets or sacrifice tissue architecture for discovery of unknown targets. To overcome these obstacles, we developed a multimodality imaging platform for discovery-based molecular histology. We apply this platform to a model of disseminated infection triggered by the pathogen Staphylococcus aureus, leading to the discovery of infection-associated alterations in the distribution and abundance of proteins and elements in tissue in mice. These data provide an unbiased, three-dimensional analysis of how disease affects the molecular architecture of complex tissues, enable culture-free diagnosis of infection through imaging-based detection of bacterial and host analytes, and reveal molecular heterogeneity at the host-pathogen interface.

Defining motility in the Staphylococci

The ability of bacteria to move is critical for their survival in diverse environments and multiple ways have evolved to achieve this. Two forms of motility have recently been described for Staphylococcus aureus, an organism previously considered to be non-motile. One form is called spreading, which is a type of sliding motility and the second form involves comet formation, which has many observable characteristics associated with gliding motility. Darting motility has also been observed in Staphylococcus epidermidis. This review describes how motility is defined and how we distinguish between passive and active motility. We discuss the characteristics of the various forms of Staphylococci motility, the molecular mechanisms involved and the potential future research directions.

Cell-Surface Phenol Soluble Modulins Regulate Staphylococcus aureus Colony Spreading

Staphylococcus aureus produces phenol-soluble modulins (PSMs), which are amphipathic small peptides with lytic activity against mammalian cells. We previously reported that PSMα1-4 stimulate S. aureus colony spreading, the phenomenon of S. aureus colony expansion on the surface of soft agar plates, whereas δ-toxin (Hld, PSMγ) inhibits colony-spreading activity. In this study, we revealed the underlying mechanism of the opposing effects of PSMα1-4 and δ-toxin in S. aureus colony spreading. PSMα1-4 and δ-toxin are abundant on the S. aureus cell surface, and account for 18% and 8.5% of the total amount of PSMα1-4 and δ-toxin, respectively, in S. aureus overnight cultures. Knockout of PSMα1-4 did not affect the amount of cell surface δ-toxin. In contrast, knockout of δ-toxin increased the amount of cell surface PSMα1-4, and decreased the amount of culture supernatant PSMα1-4. The δ-toxin inhibited PSMα3 and PSMα2 binding to the S. aureus cell surface in vitro. A double knockout strain of PSMα1-4 and δ-toxin exhibited decreased colony spreading compared with the parent strain. Expression of cell surface PSMα1-4, but not culture supernatant PSMα1-4, restored the colony-spreading activity of the PSMα1-4/δ-toxin double knockout strain. Expression of δ-toxin on the cell surface or in the culture supernatant did not restore the colony-spreading activity of the PSMα1-4/δ-toxin double knockout strain. These findings suggest that cell surface PSMα1-4 promote S. aureus colony spreading, whereas δ-toxin suppresses colony-spreading activity by inhibiting PSMα1-4 binding to the S. aureus cell surface.