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1. (Article ID: 5398)
 
Arbatsky NP, Kenyon JJ, Shashkov AS, Shneider MM, Popova AV, Kalinchuk NA, Hall RM, Knirel YA
The K5 capsular polysaccharide of the bacterium Acinetobacter baumannii SDF with the same K unit containing Leg5Ac7Ac as the K7 capsular polysaccharide but a different linkage between the K units
Russian Chemical Bulletin = Izvestiia Akademii nauk. Seriia khimicheskaia 68(1) (2019) 163-167
 

The K5 capsular polysaccharide (CPS) was isolated from the bacterium Acinetobacter baumannii (A. baumannii) SDF and studied by 1D and 2D 1H and 13C NMR spectroscopy before and after O-deacetylation and partial acid hydrolysis. The CPS was found to be composed of branched tetrasaccharide repeats (K units) containing 5,7-diacetamido-3,5,7,9-tetradeoxy-d-glycero-d-galacto-non-2-ulosonic acid (Leg5Ac7Ac). The KL5 capsule biosynthesis gene cluster at the K locus is consistent with the composition and structure of the CPS. KL5 is almost identical to the KL7 gene ulosonic acid (Leg5Ac7Ac A. baumannii LUH5533 that has been characterized earlier, and differs only in the gene for Wzy polymerase that is responsible for the formation of the linkage between the K units. The K5 CPS from strain SDF and the K7 CPS from strain LUH5533 have the same K-unit structure but a different linkage between the K units, which is formed by distinct Wzy polymerases. As opposite to Leg5Ac7Ac in the K7 CPS, this monosaccharide is O-acetylated at position 4 in the K5 CPS. No acetyltransferase for this modification of the K5 CPS is present in the KL5 gene cluster, and hence it is encoded by a gene located elsewhere in the genome.

Acinetobacter baumannii, capsular polysaccharide, legionaminic acid, Wzy polymerase, gene polymorphism, KL gene locus

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2. (Article ID: 5459)
 
Kenyon JJ, Arbatsky NP, Shneider MM, Popova AV, Dmitrenok AS, Kasimova AA, Shashkov AS, Hall RM, Knirel YA
The K46 and K5 capsular polysaccharides produced by Acinetobacter baumannii NIPH 329 and SDF have related structures and the side-chain non-ulosonic acids are acetylated by phage-encoded acetyltransferases
PLoS One 14(6) (2019) 0218461
 

Acinetobacter baumannii isolate NIPH 329 carries a novel capsular polysaccharide (CPS) gene cluster, designated KL46, that is closely related to the KL5 locus in A. baumannii isolate SDF but includes genes for synthesis of 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic (di-N-acetylpseudaminic) acid (Pse5Ac7Ac) instead of the corresponding D-glycero-D-galacto isomer (di-N-acetyllegionaminic acid) (Leg5Ac7Ac). In agreement with the genetic content of KL46, chemical studies of the K46 CPS produced by NIPH 329 revealed a branched tetrasaccharide repeat (K unit) with an overall structure the same as K5 from SDF but with β-Pse5Ac7Ac replacing α-Leg5Ac7Ac. As for K5, the K46 unit begins with d-GalpNAc and includes α-d-GlcpNAc-(1→3)-d-GalpNAc and α-d-Galp-(1→6)-d-GlcpNAc linkages, formed by Gtr14 and Gtr15 glycosyltransferases, respectively. The Gtr94K46 glycosyltransferase, which is related to Gtr13K5, links Pse5Ac7Ac to d-Galp in the growing K unit via a β-(2→6) linkage. Nearly identical Wzy enzymes connect the K46 and K5 units via a α-D-GalpNAc-(1→3)-α-D-Galp linkage to form closely related CPSs. Both Pse5Ac7Ac in K46 and Leg5Ac7Ac in K5 are acetylated at O4 but no acetyltransferase gene is present in KL46 or KL5. Related acetyltransferases were found encoded in the NIPH 329 and SDF genomes, but not in other strains carrying an unacetylated Pse or Leg derivative in the CPS. The genes encoding the acetyltransferases were in different putative phage genomes. However, related acetyltransferases were rare among the >3000 publically available genome sequences.

biosynthesis, locus, Acinetobacter baumannii, capsular polysaccharide, gene cluster, nonulosonic acid, glycosyltransferase

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3. (Article ID: 5493)
 
Senchenkova SN, Kenyon JJ, Jia TY, Popova AV, Shneider MM, Kasimova AA, Shashkov AS, Liu B, Hall RM, Knirel YA
The K90 capsular polysaccharide produced by Acinetobacter baumannii LUH5553 contains di-N-acetylpseudaminic acid and is structurally related to the K7 polysaccharide from A. baumannii LUH5533
Carbohydrate Research 479(1) (2019) 1-5
 

Acinetobacter baumannii isolate LUH5553 carries the KL90 capsule gene cluster, which includes genes for three glycosyltransferases (Gtrs) and the ItrA3 initiating transferase, as well as a set of genes for synthesis of a higher sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-non-2-ulosonic (di-N-acetylpseudaminic) acid (Pse5Ac7Ac). The K90 capsular polysaccharide (CPS) has a tetrasaccharide repeat (K90 unit), which begins with d-GlcpNAc and contains Pse5Ac7Ac. The higher sugar was cleaved by mild acid hydrolysis of the CPS, and structures of the initial and modified polysaccharides were established by 1D and 2D 1H and 13C NMR spectroscopy. K90 contains α-d-Galp-(1-6)-d-GlcpNAc and α-d-GlcpNAc-(1-3)-d-GlcpNAc fragments, and formation of these glycosidic linkages is catalysed respectively by Gtr14 and Gtr15. The gtr14 and gtr15 genes occur in several A. baumannii KL gene clusters, including KL5 and KL7 that carry itrA2 rather than itrA3. As ItrA2 introduces d-GalpNAc rather than d-GlcpNAc as the first monosaccharide, Gtr15 can transfer d-GlcpNAc to either of these amino sugars, suggesting that this enzyme has relaxed specificity. Consequently, the third, novel glycosyltransferase, Gtr163, forms the β-(2-3) linkage between Pse5Ac7Ac and d-Galp. Wzy polymerases encoded by KL90 and KL7 are 54% identical and form the same linkage between the K units to give branched polysaccharides with the same main chain but different disaccharide side chains, β-Pse5Ac7Ac-(2-3)-d-Galp in K90 and α-Leg5Ac7Ac-(2-6)-d-Galp in K7.

Acinetobacter baumannii, capsular polysaccharide, Di-N-Acetylpseudaminic acid, KL90 gene cluster

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4. (Article ID: 5791)
 
Knirel YA, Van Calsteren M
Bacterial exopolysaccharides
Book: Comprehensive Glycoscience: From Chemistry to Systems Biology. Reference Module in Chemistry, Molecular Sciences and Chemical Engineering (2021) 1-75
 

Bacterial extracellular polysaccharides are known as a cell-bound capsule, a sheath, or a slime, which is excreted into the environment. They play an important role in virulence of medical bacteria and plant-to-symbiont interaction and are used for serotyping of bacteria and production of vaccines. Some exopolysaccharides have commercial applications in industry, and claims of health benefits have been documented for an increasing number of them. Exopolysaccharides have diverse composition and structure, and some contain sugar and non-sugar components that are found in bacterial carbohydrates only. The present article provides an updated collection of the data on exopolysaccharides of various classes of gram-negative and gram-positive bacteria reported until the end of 2019. When known, biosynthesis pathways of exopolysaccharides are treated in a summary manner. References are made to structure and biosynthesis relatedness between exopolysaccharides of different bacterial taxa as well as between bacterial polysaccharides and mammalian glycosaminoglycans.

polysaccharide structure, Gram-negative bacteria, capsule, Biofilm, polysaccharide biosynthesis, gram-positive bacteria, Monosaccharide composition, Bacterial exopolysaccharide, non-sugar component

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5. (Article ID: 6413)
 
Knirel YA, Kasimova AA, Arbatsky NP, Shneider MM, Popova AV, Brovko FA, Shashkov AS, Senchenkova SN, Perepelov AV, Shpirt AM
5,7-Diamino-3,5,7,9-tetradeoxynon-2-ulosonic Acids in the Capsular Polysaccharides of Acinetobacter baumannii
Biochemistry (Moscow) 88(2) (2023) 202-210
 

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

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