Bacteriophage Tail-Spike Proteins Enable Detection of Pseudaminic-Acid-Coated Pathogenic Bacteria and Guide the Development of Antiglycan Antibodies with Cross-Species Antibacterial Activity

The three-sided right-handed β-helix is a versatile fold for glycan interactions

Interactions between proteins and glycans are critical to various biological processes. With databases of carbohydrate-interacting proteins and increasing amounts of structural data, the three-sided right-handed β-helix (RHBH) has emerged as a significant structural fold for glycan interactions. In this review, we provide an overview of the sequence, mechanistic, and structural features that enable the RHBH to interact with glycans. The RHBH is a prevalent fold that exists in eukaryotes, prokaryotes, and viruses associated with adhesin and carbohydrate-active enzyme (CAZyme) functions. An evolutionary trajectory analysis on structurally characterized RHBH-containing proteins shows that they likely evolved from carbohydrate-binding proteins with their carbohydrate-degrading activities evolving later. By examining three polysaccharide lyase and three glycoside hydrolase structures, we provide a detailed view of the modes of glycan binding in RHBH proteins. The 3-dimensional shape of the RHBH creates an electrostatically and spatially favorable glycan binding surface that allows for extensive hydrogen bonding interactions, leading to favorable and stable glycan binding. The RHBH is observed to be an adaptable domain capable of being modified with loop insertions and charge inversions to accommodate heterogeneous and flexible glycans and diverse reaction mechanisms. Understanding this prevalent protein fold can advance our knowledge of glycan binding in biological systems and help guide the efficient design and utilization of RHBH-containing proteins in glycobiology research.

Bacterial pseudaminic acid binding to Siglec-10 induces a macrophage interleukin-10 response and suppresses phagocytosis

Pseudaminic acid (Pse) on pathogenic bacteria exopolysaccharide engages with the sialic acid-binding immunoglobulin-type lectin (Siglec)-10 receptor on macrophages via the critical 7-N-acetyl group. This binding stimulates macrophages to secrete interleukin 10 that suppresses phagocytosis against bacteria, but can be reverted by blocking Pse-Siglec-10 interaction with Pse-binding protein as a promising therapy.

Dual DNA recycling amplifications coupled with Au NPs@ZIF-MOF accelerator for enhanced electrochemical ratiometric sensing of pathogenic bacteria

Sensitive and accurate quantification of pathogenic bacteria is vastly significant to the related food safety. Herein, a sensitive ratiometric electrochemical biosensor was developed for the detection of Staphylococcus aureus (S. aureus) based on dual DNA recycling amplifications and Au NPs@ZIF-MOF accelerator. Gold nanoparticles-loaded Zeolitic imidazolate metal-organic framework (Au NPs@ZIF-MOF) as electrode substrate possessed a large specific surface area for nucleic acid adsorption, and as an accelerator promoted the transfer of electrons. The strong recognition of aptamer to target S. aureus could initiate the padlock probe-based exponential rolling circle amplification (P-ERCA, as the first DNA recycling amplification), generating large numbers of trigger DNA strands. The released trigger DNA further activated the catalytic hairpin assembly (CHA, as the second DNA recycling amplification) on electrode surface. Consequently, P-ERCA and CHA continuously brought about one target to many signal transduction, leading to an exponential amplification. To achieve the accuracy of detection, the signal ratio of methylene blue (MB) and ferrocene (Fc) (I_MB/I_Fc) was applied for intrinsic self-calibrating. Taking advantages of dual DNA recycling amplifications and Au NPs@ZIF-MOF, the proposed sensing system displayed high sensitivity for S. aureus quantification with a linear range of 5-10⁸ CFU/mL, and the limit of detection was 1 CFU/mL. Moreover, this system represented excellent reproducibility, selectivity, and practicability for S. aureus analysis in foods.

The K218 capsular polysaccharide produced by Acinetobacter baumannii isolate 52-249 includes 5,7-di-N-acetylpseudaminic acid linked by a KpsS3 glycosyltransferase

Two acylated forms of the higher sugar, 5,7-diamino-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic acid called pseudaminic acid, Pse5Ac7Ac and Pse5Ac7RHb where R indicates (R)-3-hydroxybutanoyl, have been found to occur in many capsular polysaccharide (CPS) types produced by isolates of an important human pathogen, Acinetobacter baumannii. The presence of either a psaABCEDF or psaABCGHF gene module at the K locus (KL) for CPS biosynthesis determines the type of the variant produced. Here, an A. baumannii clinical isolate 52-249, recovered in 2015 in Moscow, Russia, was found to include a novel psaABCIJF gene module in the KL218 sequence at the K locus. The CPS from 52-249 was extracted and studied by sugar analysis and partial acid hydrolysis along with one- and two-dimensional ¹H and ¹³C NMR spectroscopy. A branched tetrasaccharide repeating unit was identified, which included a →3)-α-d-Galp-(1→6)-α-d-GlcpNAc-(1→3)-β-d-GalpNAc-(1→ main chain and Pse5Ac7Ac attached as a side branch, indicating that the psaABCIJF gene module is associated with synthesis of this variant. The K218 CPS was found to be structurally related to the K46 CPS of A. baumannii, and a comparison of the two structures enabled the assignment of glycosyltransferases. A KpsS3 protein for the α-(2→6) linkage of the Pse5Ac7Ac residue to D-Galp in K218 was identified.

Bacteriophage Tail Proteins as a Tool for Bacterial Pathogen Recognition—A Literature Review

In recent years, a number of bacterial detection methods have been developed to replace time-consuming culture methods. One interesting approach is to mobilize the ability of phage tail proteins to recognize and bind to bacterial hosts. In this paper, the authors provide an overview of the current methodologies in which phage proteins play major roles in detecting pathogenic bacteria. Authors focus on proteins capable of recognizing highly pathogenic strains, such as Acinetobacter baumannii, Campylobacter spp., Yersinia pestis, Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus, Enterococcus spp., Salmonella spp., and Shigella. These pathogens may be diagnosed by capture-based detection methods involving the use of phage protein-coated nanoparticles, ELISA (enzyme-linked immunosorbent assay)-based methods, or biosensors. The reviewed studies show that phage proteins are becoming an important diagnostic tool due to the discovery of new phages and the increasing knowledge of understanding the specificity and functions of phage tail proteins.