Lectin activity of the pneumococcal pilin proteins

Integrated genomic analysis of antibiotic resistance and virulence determinants in invasive strains of Streptococcus pneumoniae

Introduction

Streptococcus pneumoniae is an important human pathogen that may cause severe invasive pneumococcal diseases (IPDs) in young children and the elderly. A comprehensive comparative whole-genome analysis of invasive and non-invasive serotype strains offers great insights that are applicable to vaccine development and disease control.

Methods

In this study, 58 invasive (strains isolated from sterile sites) and 71 non-invasive (serotypes that have not been identified as invasive in our study) pneumococcal isolates were identified among the 756 pneumococcal isolates obtained from seven hospitals in Zhejiang, China (2010-2022). Serotyping, antimicrobial resistance tests, and genomic analyses were conducted to characterize these strains.

Results and discussion

The three most invasive serotypes were 23F, 14, and 6B. The invasive pneumococcal isolates' respective resistance rates against penicillin, ceftriaxone, tetracycline, and erythromycin were 34.5%, 15.5%, 98.3%, and 94.7%. Whole-genome sequencing indicated that the predominant invasive clonal complexes were CC271, CC876, and CC81. The high rate of penicillin non-susceptible Streptococcus pneumoniae (PNSP) is related to the clonal distribution of resistance-conferring penicillin-binding proteins (PBP). Interestingly, we found a negative correlation between invasiveness and resistance in the invasive pneumococcal serotype strains, which might be due to the proclivity of certain serotypes to retain their β-lactam resistance. Moreover, the mutually exclusive nature of zmpC and rrgC+srtBCD suggests their intricate and potentially redundant roles in promoting the development of IPD. These findings reveal significant implications for pneumococcal vaccine development in China, potentially informing treatment strategies and measures to mitigate disease transmission.

One, two, many: Strategies to alter the number of carbohydrate binding sites of lectins

Carbohydrates are more than an energy-storage. They are ubiquitously found on cells and most proteins, where they encode biological information. Lectins bind these carbohydrates and are essential for translating the encoded information into biological functions and processes. Hundreds of lectins are known, and they are found in all domains of life. For half a century, researchers have been preparing variants of lectins in which the binding sites are varied. In this way, the traits of the lectins such as the affinity, avidity and specificity towards their ligands as well as their biological efficacy were changed. These efforts helped to unravel the biological importance of lectins and resulted in improved variants for biotechnological exploitation and potential medical applications. This review gives an overview on the methods for the preparation of artificial lectins and complexes thereof and how reducing or increasing the number of binding sites affects their function.

Host-informed therapies for the treatment of pneumococcal pneumonia

Over the past two decades, traditional antimicrobial strategies have lost efficacy due to a rapid rise in antibiotic resistance and limited success in developing new antibiotics. Rather than relying on therapeutics solely targeting the bacterial pathogen, therapies are emerging that simultaneously focus on host responses. Here, we describe the most promising 'host-informed therapies' (HITs) in two categories: those that aid patients with fully functional immune systems, and those that aid patients with perturbed immune processes. Using Streptococcus pneumoniae, the leading cause of bacterial pneumonia, as a case study, we show HITs as an attractive option for supplementing infection management. However, to broaden their applicability and design new strategies, targeted research and clinical trials will be essential.

Mucin Binding to Moraxella catarrhalis During Airway Inflammation is Dependent on Sialic Acid

Chronic obstructive pulmonary disease (COPD) is associated with colonization by bacterial pathogens and repeated airway infections, leading to exacerbations and impaired lung function. The highly glycosylated mucins in the mucus lining the airways are an important part of the host defense against pathogens. However, mucus accumulation can contribute to COPD pathology. Here, we examined whether inflammation is associated with glycosylation changes that affect interactions between airway mucins and pathogens. We isolated mucins from lower airway samples (LAS, n=4-9) from long-term smokers with and without COPD and from never-smokers. The most abundant terminal glycan moiety was N-acetylneuraminic acid (Neu5Ac) among smokers with and without COPD and N-acetyl-hexoseamine among never-smokers. Moraxella catarrhalis bound to MUC5 mucins from smokers with and without COPD. M. catarrhalis binding correlated with inflammatory parameters and Neu5Ac content. M. catarrhalis binding was abolished by enzymatic removal of Neu5Ac. Furthermore, M. catarrhalis bound to α2-6 sialyl-lactose suggesting that α2-6 sialic acid contributes to M. catarrhalis binding to mucins. Further, we detected more M. catarrhalis binding to mucins from patients with pneumonia than to those from control subjects (n=8-13) and this binding correlated with C-reactive protein and Neu5Ac levels. These results suggest a key role of inflammation induced Neu5Ac in adhesion of M. catarrhalis to airway mucins. Inflammation induced ability of MUC5 mucins to bind M. catarrhalis is likely a host defense mechanism in the healthy lung, although it cannot be excluded that impaired mucociliary clearance limits the effectiveness of this defense in COPD patients.

Streptococcus pneumoniae Type 1 Pilus - A Multifunctional Tool for Optimized Host Interaction

Streptococcus pneumoniae represents a major Gram-positive human pathogen causing bacterial pneumonia, otitis media, meningitis, and other invasive diseases. Several pneumococcal isolates show increasing resistance rates against antibacterial agents. A variety of virulence factors promote pneumococcal pathogenicity with varying importance in different stages of host infection. Virulence related hair-like structures ("pili") are complex, surface located protein arrays supporting proper host interaction. In the last two decades different types of pneumococcal pili have been identified: pilus-1 (P1) and pilus-2 (P2) are formed by the catalytic activity of sortases that covalently assemble secreted polypeptide pilin subunits in a defined order and finally anchor the resulting pilus in the peptidoglycan. Within the long pilus fiber the presence of intramolecular isopeptide bonds confer high stability to the sequentially arranged individual pilins. This mini review will focus on S. pneumoniae TIGR4 P1 molecular architecture, the subunits it builds and provides insights into P1 sortase-mediated assembly. The complex P1 architecture (anchor-/backbone-/tip-subunits) allows the specific interaction with various target structures facilitating different steps of colonization, invasion and spreading within the host. Optimized pilin subunit confirmation supports P1 function under physiological conditions. Finally, aspects of P1- host interplay are summarized, including recent insights into P1 mechanobiology, which have important implications for P1 mediated pathogenesis.

The impact of the ancillary pilus-1 protein RrgA of Streptococcus pneumoniae on colonization and disease

The Gram-positive bacterium Streptococcus pneumoniae, the pneumococcus, is an important commensal resident of the human nasopharynx. Carriage is usually asymptomatic, however, S. pneumoniae can become invasive and spread from the upper respiratory tract to the lungs causing pneumonia, and to other organs to cause severe diseases such as bacteremia and meningitis. Several pneumococcal proteins important for its disease-causing capability have been described and many are expressed on the bacterial surface. The surface located pneumococcal type-1 pilus has been associated with virulence and the inflammatory response, and it is present in 20%-30% of clinical isolates. Its tip protein RrgA has been shown to be a major adhesin to human cells and to promote invasion through the blood-brain barrier. In this review we discuss recent findings of the impact of RrgA on bacterial colonization of the upper respiratory tract and on pneumococcal virulence, and use epidemiological data and genome-mining to suggest trade-off mechanisms potentially explaining the rather low prevalence of pilus-1 expressing pneumococci in humans.

Lectin Activity of the TcdA and TcdB Toxins of Clostridium difficile

Clostridium difficile is a major cause of hospital-acquired antibiotic-associated diarrhea. C. difficile produces two cytotoxins, TcdA and TcdB; both toxins are multidomain proteins that lead to cytotoxicity through the modification and inactivation of small GTPases of the Rho/Rac family. Previous studies have indicated that host glycans are targets for TcdA and TcdB, with interactions thought to be with both α- and β-linked galactose. In the current study, screening of glycan arrays with different domains of TcdA and TcdB revealed that the binding regions of both toxins interact with a wider range of host glycoconjugates than just terminal α- and β-linked galactose, including blood groups, Lewis antigens, N-acetylglucosamine, mannose, and glycosaminoglycans. The interactions of TcdA and TcdB with ABO blood group and Lewis antigens were assessed by surface plasmon resonance (SPR). The blood group A antigen was the highest-affinity ligand for both toxins. Free glycans alone or in combination were unable to abolish Vero cell cytotoxicity by TcdB. SPR competition assays indicate that there is more than one glycan binding site on TcdB. Host glycoconjugates are common targets of bacterial toxins, but typically this binding is to a specific structure or related structures. The binding of TcdA and TcdB is to a wide range of host glycans providing a wide range of target cells and tissues in vivo.

The Role of Glycans in Bacterial Adhesion to Mucosal Surfaces: How Can Single-Molecule Techniques Advance Our Understanding?

Bacterial adhesion is currently the subject of increased interest from the research community, leading to fast progress in our understanding of this complex phenomenon. Resent research within this field has documented the important roles played by glycans for bacterial surface adhesion, either through interaction with lectins or with other glycans. In parallel with this increased interest for and understanding of bacterial adhesion, there has been a growth in the sophistication and use of sensitive force probes for single-molecule and single cell studies. In this review, we highlight how the sensitive force probes atomic force microscopy (AFM) and optical tweezers (OT) have contributed to clarifying the mechanisms underlying bacterial adhesion to glycosylated surfaces in general and mucosal surfaces in particular. We also describe research areas where these techniques have not yet been applied, but where their capabilities appear appropriate to advance our understanding.

Specificity and utility of SubB2M, a new N-glycolylneuraminic acid lectin

The B subunit of the subtilase cytotoxin (SubB) recognises N-glycolylneuraminic acid (Neu5Gc) containing glycans, the most prominent form of aberrant glycosylation in human cancers. We have previously engineered SubB by construction of a SubB_{ΔS106/ΔT107} mutant (SubB2M) for greater specificity and enhanced recognition of Neu5Gc containing glycans. In this study, we further explore the utility of SubB2M as a Neu5Gc lectin by showing its improved specificity and recognition for Neu5Gc containing glycans over the wild-type SubB protein and an anti-Neu5Gc IgY antibody in a N-acetylneuraminic acid (Neu5Ac)/Neu5Gc glycan array and by surface plasmon resonance. Far-western blot analysis showed that SubB2M preferentially binds to bovine serum glycoproteins over human serum glycoproteins. SubB2M was also able to detect Neu5Gc containing bovine glycoproteins spiked into normal human serum with greater sensitivity than the wild-type SubB and the anti-Neu5Gc IgY antibody. These results suggest that SubB2M will be a useful tool for the testing of serum and other bodily fluids for cancer diagnosis and prognosis.