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A structurally diverse capsular polysaccharide (CPS) in the outer cell envelope plays an important role in the virulence of the important bacterial pathogen, Acinetobacter baumannii. More than 75 different CPS structures have been determined for the species to date, and many CPSs include isomers of a higher sugar, namely 5,7-diamino-3,5,7,9-tetradeoxynon-2-ulosonic acid. Recently, a novel isomer having the D-glycero-L-manno configuration (5,7-di-N-acetyl-8-epipseudaminic acid; 8ePse5Ac7Ac) has been identified in the CPS from A. baumannii clinical isolate RES-546 [Carbohydr. Res. 513 (2022) 108,531]. Here, the complete chemical structure of this CPS, designated K135, was elucidated. The CPS was found to have a branched tetrasaccharide K unit and to include the higher sugar as part of a 8ePse5Ac7Ac-(2→6)-α-Gal disaccharide branching from a →3)-α-D-GlcpNAc-(1→3)-β-D-GlcpNAc-(1→ main chain. Assignment of glycosyltransferases encoded by the CPS biosynthesis gene cluster in the RES-546 genome enabled the first sugar of the K unit, and hence the topology of the K135 CPS, to be determined.

Acinetobacter baumannii, capsular polysaccharide, 5, 7, 9-tetradeoxynon-2-ulosonic acid, 7-diacetamido-3, K135

NCBI PubMed ID: 36446189
Publication DOI: 10.1016/j.carres.2022.108726
Journal NLM ID: 0043535
Publisher: Elsevier
Correspondence: J.J. Kenyon
Institutions: N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia, Centre for Immunology and Infection Control, School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Australia, State Research Center for Applied Microbiology and Biotechnology, Obolensk, Moscow, Region, Russia, M.M. Shemyakin & Y. A Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
Methods: 13C NMR, 1H NMR, NMR-2D, sugar analysis, acid hydrolysis, GLC, Smith degradation, GPC, bioinformatic analysis

The polysaccharide capsule surrounding bacterial cell plays an important role in pathogenesis of infections caused by the opportunistic pathogen Acinetobacter baumannii by providing protection from external factors. The structures of the capsular polysaccharide (CPS) produced by A. baumannii isolates and the corresponding CPS biosynthesis gene clusters are highly diverse, although many of them are related. Many types of A. baumannii CPSs contain isomers of 5,7-diamino-3,5,7,9-tetradeoxynon-2-ulosonic acid (DTNA). Three of these isomers, namely acinetaminic acid (l-glycero-l-altro isomer), 8-epiacinetaminic acid (d-glycero-l-altro isomer), and 8-epipseudaminic acid (d-glycero-l-manno isomer), have not been found so far in naturally occurring carbohydrates from other species. In A. baumannii CPSs, DTNAs carry N-acyl substituents at positions 5 and 7; in some CPSs, both N-acetyl and N-(3-hydroxybutanoyl) groups are present. Remarkably, pseudaminic acid carries the (R)-isomer and legionaminic acid carries the (S)-isomer of the 3-hydroxybutanoyl group. The review addresses the structure and genetics of biosynthesis of A. baumannii CPSs containing di-N-acyl derivatives of DTNA.

Acinetobacter baumannii, capsular polysaccharide, nonulosonic acid, Bacterial polysaccharide, capsule, higher monosaccharide, acyl group

NCBI PubMed ID: 37072328
Publication DOI: 10.1134/S0006297923020049
Journal NLM ID: 0376536
Publisher: Nauka/Interperiodica
Correspondence: Y.A. Knirel
Institutions: State Research Center for Applied Microbiology and Biotechnology, Obolensk, Moscow Region, 142279, Russia, Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 117913, Russia, Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia, Branch of the Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry in Pushchino, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia

Acinetobacter baumannii, capsular polysaccharide, 5, 7, 9-tetradeoxynon-2-ulosonic acid, 7-diacetamido-3, K135