Structure of the K58 capsular polysaccharide produced by Acinetobacter baumannii isolate MRSN 31468 includes Pse5Ac7Ac that is 4-O-acetylated by a phage-encoded acetyltransferase

• Published in: Carbohydrate research 2025-01, Vol.547, p.109324, Article 109324
• Main Authors: Iovine, Andrea, Filatov, Andrei V., Kasimova, Anastasiya A., Sharar, Nowshin S., Ambrose, Stephanie J., Dmitrenok, Andrey S., Shneider, Mikhail M., Shpirt, Anna M., Perepelov, Andrei V., Knirel, Yuriy A., Hall, Ruth M., De Castro, Cristina, Kenyon, Johanna J.
• Format: Article
• Language: English
• Subjects: Acetylation; Acetyltransferases - chemistry; Acetyltransferases - genetics; Acetyltransferases - metabolism; Acinetobacter baumannii; Acinetobacter baumannii - chemistry; Bacterial Capsules - chemistry; Bacterial Capsules - metabolism; Bacteriophages - chemistry; Bacteriophages - enzymology; Capsular polysaccharide; Carbohydrate Sequence; K locus; K58; Polysaccharides, Bacterial - biosynthesis; Polysaccharides, Bacterial - chemistry; Polysaccharides, Bacterial - metabolism; Pseudaminic acid
• ISSN: 0008-6215; 1873-426X; 1873-426X
• DOI: 10.1016/j.carres.2024.109324

Capsular polysaccharide (CPS), a heteropolymeric carbohydrate structure present on the cell surface of most isolates of the bacterial pathogen Acinetobacter baumannii, is a major virulence determinant. Here, the CPS produced by A. baumannii MRSN 31468, which carries the KL58 CPS biosynthesis locus, was studied by sugar analysis, one- and two-dimensional 1H and 13C NMR spectroscopy. The structure was found to consist of a repeating tetrasaccharide K-unit that includes glucose (d-Glcp), galactose (d-Galp), N-acetyl-galactosamine (d-GalpNAc), and 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic acid (5,7-di-N-acetylpseudaminic acid; Pse5Ac7Ac). The CPS has a branched repeating unit with the disaccharide →3)-β-d-Glc-(1→3)-β-d-GalNAc-(1→ as the mainchain and O-6 of the Glc unit substituted with the disaccharide β-Pse5Ac7Ac-(2→6)-α-d-Gal, and Pse5Ac7Ac is partially acetylated at O-4. The presence of Pse5Ac7Ac in the K58 structure is consistent with the presence of psaA-F genes in KL58, which are responsible for Pse5Ac7Ac synthesis. 4-O-acetylation of Pse5Ac7Ac was traced to an acetyltransferase, Atr44, which was found to be closely related to Atr29 that similarly decorates Pse5Ac7Ac with 4OAc in the K46-type CPS. Atr44 like Atr29 is encoded by a gene found in a prophage. The K58 CPS produced by MRSN 31468 did not include the 8-epimer of Pse5Ac7Ac (5,7-di-N-acetyl-8-epipseudaminic acid; 8ePse5Ac7Ac) found in the closely related CPS from BAL062 that also carries KL58. Hence, the gene(s) for conversion of Pse5Ac7Ac to 8ePse5Ac7Ac must lie elsewhere. [Display omitted] •Structure of the CPS from Acinetobacter baumannii isolate MRSN31468 was determined.•Tetrasaccharide repeat units include D-Glc, D-Gal, D-GalNAc and Pse5Ac7Ac.•Structure was found to be consistent with genetic content of KL58 locus in the genome of MRSN31468.