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1. (Article ID: 5016)
 
Lee IM, Tu IF, Yang FL, Ko TP, Liao JH, Lin NT, Wu CY, Ren CT, Wang AH, Chang CM, Huang KF, Wu SH
Structural basis for fragmenting the exopolysaccharide of Acinetobacter baumannii by bacteriophage PhiAB6 tailspike protein
Scientific Reports 7 (2017) 42711
 

With an increase in antibiotic-resistant strains, the nosocomial pathogen Acinetobacter baumannii has become a serious threat to global health. Glycoconjugate vaccines containing fragments of bacterial exopolysaccharide (EPS) are an emerging therapeutic to combat bacterial infection. Herein, we characterize the bacteriophage PhiAB6 tailspike protein (TSP), which specifically hydrolyzed the EPS of A. baumannii strain 54149 (Ab-54149). Ab-54149 EPS exhibited the same chemical structure as two antibiotic-resistant A. baumannii strains. The PhiAB6 TSP-digested products comprised oligosaccharides of two repeat units, typically with stoichiometric pseudaminic acid (Pse). The 1.48-1.89-A resolution crystal structures of an N-terminally-truncated PhiAB6 TSP and its complexes with the semi-hydrolyzed products revealed a trimeric beta-helix architecture that bears intersubunit carbohydrate-binding grooves, with some features unusual to the TSP family. The structures suggest that Pse in the substrate is an important recognition site for PhiAB6 TSP. A region in the carbohydrate-binding groove is identified as the determinant of product specificity. The structures also elucidated a retaining mechanism, for which the catalytic residues were verified by site-directed mutagenesis. Our findings provide a structural basis for engineering the enzyme to produce desired oligosaccharides, which is useful for the development of glycoconjugate vaccines against A. baumannii infection.

Acinetobacter baumannii, pseudaminic acid, crystal structure, bacteriophage, glycoconjugate vaccine, Tailspike

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2. (Article ID: 5178)
 
Lee IM, Yang FL, Chen TL, Liao KS, Ren CT, Lin NT, Chang YP, Wu CY, Wu SH
Pseudaminic acid on exopolysaccharide of Acinetobacter baumannii plays a critical role in phage-assisted preparation of glycoconjugate vaccine with high antigenicity
Journal of the American Chemical Society 140(28) (2018) 8639-8643
 

Pseudaminic acid (Pse) has been known for participating in crucial bacterial virulence and thus is an attractive target in the development of glycoconjugate vaccine. Particularly, this therapeutic alternative was suggested to be a potential solution against antibiotic resistant Acinetobacter baumannii that poses a serious global health threat. Also, Pse was found to be involved in the exopolysaccharide (EPS) of mild antibiotic resistant Acinetobacter baumannii strain 54149 (Ab-54149) of which specific glycosyl linkage can be depolymerized by phagePhiAB6 tailspike protein (PhiAB6TSP). In this study, we found that the antibodies induced by Ab-54149 EPS was capable of recognizing a range of EPS of other clinical A. baumannii strains, and deemed as a great potential material for vaccination. To efficiently acquire homogeneous EPS-derived oligosaccharide with significant immunogenic activity for the production of glycoconjugate, we used the PhiAB6TSP for the fragmentation of Ab-54149 EPS instead of chemical methods. Moreover, insight into the ligand binding characterization of PhiAB6TSP suggested the branched Pse on the Ab-54149 EPS served as a recognition site of PhiAB6TSP. The serum boosted by PhiAB6TSP-digested product and carrier protein CRM197 conjugate complex displayed specific sensitivity toward Ab-54149 EPS with bacterial killing activity. Strikingly, Pse is an ideal epitope with strong antigenicity, profiting the application of the probe for pathogen detection and glyco-based vaccine.

Acinetobacter baumannii, pseudaminic acid, exopolysaccharide, vaccine, CRM197, glycoconjugate vaccine

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3. (Article ID: 6211)
 
Del Bino L, Osterlid KE, Wu DY, Nonne F, Romano MR, Codée J, Adamo R
Synthetic Glycans to Improve Current Glycoconjugate Vaccines and Fight Antimicrobial Resistance
Chemical Reviews 122(20) (2022) 15672-15716
 

Antimicrobial resistance (AMR) is emerging as the next potential pandemic. Different microorganisms, including the bacteria Acinetobacter baumannii, Clostridioides difficile, Escherichia coli, Enterococcus faecium, Klebsiella pneumoniae, Neisseria gonorrhoeae, Pseudomonas aeruginosa, non-typhoidal Salmonella, and Staphylococcus aureus, and the fungus Candida auris, have been identified by the WHO and CDC as urgent or serious AMR threats. Others, such as group A and B Streptococci, are classified as concerning threats. Glycoconjugate vaccines have been demonstrated to be an efficacious and cost-effective measure to combat infections against Haemophilus influenzae, Neisseria meningitis, Streptococcus pneumoniae, and, more recently, Salmonella typhi. Recent times have seen enormous progress in methodologies for the assembly of complex glycans and glycoconjugates, with developments in synthetic, chemoenzymatic, and glycoengineering methodologies. This review analyzes the advancement of glycoconjugate vaccines based on synthetic carbohydrates to improve existing vaccines and identify novel candidates to combat AMR. Through this literature survey we built an overview of structure-immunogenicity relationships from available data and identify gaps and areas for further research to better exploit the peculiar role of carbohydrates as vaccine targets and create the next generation of synthetic carbohydrate-based vaccines.

carbohydrates, glycan, glycoconjugate vaccine

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4. (Article ID: 6469)
 
Sun K, Lian M, Li Q, Wang R, Gu Y, Lei P, He H, Xu H, Sha F, Sun L
Characterization of a novel exopolysaccharide from Acinetobacter rhizosphaerae with ability to enhance the salt stress resistance of rice seedlings
International Journal of Biological Macromolecules (2023) 128438
 

We here describe the isolation of a novel exopolysaccharide from Acinetobacter rhizosphaerae, named ArEPS. The structure of ArEPS was characterized by analysis of the monosaccharide composition, molecular weight, infrared spectrum, methylation, and nuclear magnetic resonance spectrum. ArEPS was found to be an acidic heteropolysaccharide composed of glucose, galactose, galacturonic acid, glucuronic acid, mannose, and glucosamine; the molecular weight was 1533 kDa. Structural analysis showed that the main-chain structure of ArEPS predominantly comprised 1,3,6-β-Glcp, 1,3,4-α-Galp, 1,2-β-Glcp, 1,4-β-GlcpA, 1,4-β-GalpA, and the side-chain structure comprised 1,6-β-Glcp, 1,3-β-Galp, 1-α-Glcp, 1-β-Galp, 1-α-Manp, 1,4,6-α-Glcp, 1,2,4-β-Glcp, 1,2,3-β-Glcp, and 1,3-β-GlcpN. ArEPS significantly enhanced the tolerance of rice seedlings to salt stress. Specifically, plant height, fresh weight, chlorophyll content, and the K+/Na+ ratio increased by 51 %, 63 %, 29 %, and 162 %, respectively, and the malondialdehyde content was reduced by 45 % after treatment with 100 mg/kg ArEPS compared to treatment with 100 mM NaCl. Finally, based on the quadratic regression between fresh weight and ArEPS addition, the optimal ArEPS addition level was estimated to be 135.12 mg/kg. These results indicate the prospects of ArEPS application in agriculture.

exopolysaccharides, Structural characterization, salt stress alleviation

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