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Allelic polymorphisms in a glycosyltransferase gene shape glycan repertoire in the O-linked protein glycosylation system of Neisseria.

ABSTRACT: Glycosylation of multiple proteins via O-linkage is well documented in bacterial species of Neisseria of import to human disease. Recent studies of protein glycosylation (pgl) gene distribution established that related protein glycosylation systems occur throughout the genus including nonpathogenic species. However, there are inconsistencies between pgl gene status and observed glycan structures. One of these relates to the widespread distribution of pglG, encoding a glycosyltransferase that in Neisseria elongata subsp. glycolytica is responsible for the addition of di-N-acetyl glucuronic acid at the third position of a tetrasaccharide. Despite pglG residing in strains of N. gonorrhoeae, N. meningitidis and N. lactamica, no glycan structures have been correlated with its presence in these backgrounds. Moreover, PglG function in N. elongata subsp. glycolytica minimally requires UDP-glucuronic acid (GlcNAcA), and yet N. gonorrhoeae, N. meningitidis and N. lactamica lack pglJ, the gene whose product is essential for UDP-GlcNAcA synthesis. We examined the functionality of pglG alleles from species spanning the Neisseria genus by genetic complementation in N. elongata subsp. glycolytica. The results indicate that select pglG alleles from N. meningitidis and N. lactamica are associated with incorporation of an N-acetyl-hexosamine at the third position and reveal the potential for an expanded glycan repertoire in those species. Similar experiments using pglG from N. gonorrhoeae failed to find any evidence of function suggesting that those alleles are missense pseudogenes. Taken together, the results are emblematic of how allelic polymorphisms can shape bacterial glycosyltransferase function and demonstrate that such alterations may be constrained to distinct phylogenetic lineages.

SUBMITTER: Wang N

PROVIDER: S-EPMC8091471 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Species within the genus Neisseria display significant glycan diversity associated with the O-linked protein glycosylation (pgl) systems due to phase variation and polymorphic genes and gene content. The aim of this study was to examine in detail the pgl genotype and glycosylation phenotype in meningococcal isolates and the changes occurring during short-term asymptomatic carriage. Paired meningococcal isolates derived from 50 asymptomatic meningococcal carriers, taken about 2 months apart, were analyzed with whole-genome sequencing. The O-linked protein glycosylation genes were characterized in detail using the Genome Comparator tool at the https://pubmlst.org/ database. Immunoblotting with glycan-specific antibodies (Abs) was used to investigate the protein glycosylation phenotype. All major pgl locus polymorphisms identified in Neisseria meningitidis to date were present in our isolate collection, with the variable presence of pglG and pglH, both in combination with either pglB or pglB2 We identified significant changes and diversity in the pgl genotype and/or glycan phenotype in 96% of the paired isolates. There was also a high degree of glycan microheterogeneity, in which different variants of glycan structures were found at a given glycoprotein. The main mechanism responsible for the observed differences was phase-variable expression of the involved glycosyltransferases and the O-acetyltransferase. To our knowledge, this is the first characterization of the pgl genotype and glycosylation phenotype in a larger strain collection. This report thus provides important insight into glycan diversity in N. meningitidis and into the phase variability changes that influence the expressed glycoform repertoire during meningococcal carriage.IMPORTANCE Bacterial meningitis is a serious global health problem, and one of the major causative organisms is Neisseria meningitidis, which is also a common commensal in the upper respiratory tract of healthy humans. In bacteria, numerous loci involved in biosynthesis of surface-exposed antigenic structures that are involved in the interaction between bacteria and host are frequently subjected to homologous recombination and phase variation. These mechanisms are well described in Neisseria, and phase variation provides the ability to change these structures reversibly in response to the environment. Protein glycosylation systems are becoming widely identified in bacteria, and yet little is known about the mechanisms and evolutionary forces influencing glycan composition during carriage and disease.

Project description:UnlabelledBroad-spectrum O-linked protein glycosylation is well characterized in the major Neisseria species of importance to human health and disease. Within strains of Neisseria gonorrhoeae, N. meningitidis, and N. lactamica, protein glycosylation (pgl) gene content and the corresponding oligosaccharide structure are fairly well conserved, although intra- and interstrain variability occurs. The status of such systems in distantly related commensal species, however, remains largely unexplored. Using a strain of deeply branching Neisseria elongata subsp. glycolytica, a heretofore unrecognized tetrasaccharide glycoform consisting of di-N-acetylbacillosamine-glucose-di-N-acetyl hexuronic acid-N-acetylhexosamine (diNAcBac-Glc-diNAcHexA-HexNAc) was identified. Directed mutagenesis, mass spectrometric analysis, and glycan serotyping confirmed that the oligosaccharide is an extended version of the diNAcBac-Glc-based structure seen in N. gonorrhoeae and N. meningitidis generated by the successive actions of PglB, PglC, and PglD and glucosyltransferase PglH orthologues. In addition, a null mutation in the orthologue of the broadly conserved but enigmatic pglG gene precluded expression of the extended glycoform, providing the first evidence that its product is a functional glycosyltransferase. Despite clear evidence for a substantial number of glycoprotein substrates, the major pilin subunit of the endogenous type IV pilus was not glycosylated. The latter finding raises obvious questions as to the relative distribution of pilin glycosylation within the genus, how protein glycosylation substrates are selected, and the overall structure-function relationships of broad-spectrum protein glycosylation. Together, the results of this study provide a foundation upon which to assess neisserial O-linked protein glycosylation diversity at the genus level.ImportanceBroad-spectrum protein glycosylation systems are well characterized in the pathogenic Neisseria species N. gonorrhoeae and N. meningitidis. A number of lines of evidence indicate that the glycan components in these systems are subject to diversifying selection and suggest that glycan variation may be driven in the context of glycosylation of the abundant and surface-localized pilin protein PilE, the major subunit of type IV pili. Here, we examined protein glycosylation in a distantly related, nonpathogenic neisserial species, Neisseria elongata subsp. glycolytica. This system has clear similarities to the systems found in pathogenic species but makes novel glycoforms utilizing a glycosyltransferase that is widely conserved at the genus level but whose function until now remained unknown. Remarkably, PilE pilin is not glycosylated in this species, a finding that raises important questions about the evolutionary trajectories and overall structure-function relationships of broad-spectrum protein glycosylation systems in bacteria.

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Allelic polymorphisms in a glycosyltransferase gene shape glycan repertoire in the O-linked protein glycosylation system of Neisseria.

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