Glycosylation substrate specificity of Pseudomonas aeruginosa 1244 pilin

CRISPRi-Mediated Silencing of Burkholderia O-Linked Glycosylation Systems Enables the Depletion of Glycosylation Yet Results in Modest Proteome Impacts

The process of O-linked protein glycosylation is highly conserved across the Burkholderia genus and mediated by the oligosaccharyltransferase PglL. While our understanding of Burkholderia glycoproteomes has increased in recent years, little is known about how Burkholderia species respond to modulations in glycosylation. Utilizing CRISPR interference (CRISPRi), we explored the impact of silencing of O-linked glycosylation across four species of Burkholderia; Burkholderia cenocepacia K56-2, Burkholderia diffusa MSMB375, Burkholderia multivorans ATCC17616, and Burkholderia thailandensis E264. Proteomic and glycoproteomic analyses revealed that while CRISPRi enabled inducible silencing of PglL, this did not abolish glycosylation, nor recapitulate phenotypes such as proteome changes or alterations in motility that are associated with glycosylation null strains, despite inhibition of glycosylation by nearly 90%. Importantly, this work also demonstrated that CRISPRi induction with high levels of rhamnose leads to extensive impacts on the Burkholderia proteomes, which without appropriate controls mask the impacts specifically driven by CRISPRi guides. Combined, this work revealed that while CRISPRi allows the modulation of O-linked glycosylation with reductions up to 90% at a phenotypic and proteome levels, Burkholderia appears to demonstrate a robust tolerance to fluctuations in glycosylation capacity.

Discovery and characterization of a new class of O-linking oligosaccharyltransferases from the Moraxellaceae family

Bacterial protein glycosylation is commonly mediated by oligosaccharyltransferases (OTases) that transfer oligosaccharides en bloc from preassembled lipid-linked precursors to acceptor proteins. Natively, O-linking OTases usually transfer a single repeat unit of the O-antigen or capsular polysaccharide to the side chains of serine or threonine on acceptor proteins. Three major families of bacterial O-linking OTases have been described: PglL, PglS, and TfpO. TfpO is limited to transferring short oligosaccharides both in its native context and when heterologously expressed in glycoengineered Escherichia coli. On the other hand, PglL and PglS can transfer long-chain polysaccharides when expressed in glycoengineered E. coli. Herein, we describe the discovery and functional characterization of a novel family of bacterial O-linking OTases termed TfpM from Moraxellaceae bacteria. TfpM proteins are similar in size and sequence to TfpO enzymes but can transfer long-chain polysaccharides to acceptor proteins. Phylogenetic analyses demonstrate that TfpM proteins cluster in distinct clades from known bacterial OTases. Using a representative TfpM enzyme from Moraxella osloensis, we determined that TfpM glycosylates a C-terminal threonine of its cognate pilin-like protein and identified the minimal sequon required for glycosylation. We further demonstrated that TfpM has broad substrate tolerance and can transfer diverse glycans including those with glucose, galactose, or 2-N-acetyl sugars at the reducing end. Last, we find that a TfpM-derived bioconjugate is immunogenic and elicits serotype-specific polysaccharide IgG responses in mice. The glycan substrate promiscuity of TfpM and identification of the minimal TfpM sequon renders this enzyme a valuable additional tool for expanding the glycoengineering toolbox.

Integrated mass spectrometry-based multi-omics for elucidating mechanisms of bacterial virulence

Despite being considered the simplest form of life, bacteria remain enigmatic, particularly in light of pathogenesis and evolving antimicrobial resistance. After three decades of genomics, we remain some way from understanding these organisms, and a substantial proportion of genes remain functionally unknown. Methodological advances, principally mass spectrometry (MS), are paving the way for parallel analysis of the proteome, metabolome and lipidome. Each provides a global, complementary assay, in addition to genomics, and the ability to better comprehend how pathogens respond to changes in their internal (e.g. mutation) and external environments consistent with infection-like conditions. Such responses include accessing necessary nutrients for survival in a hostile environment where co-colonizing bacteria and normal flora are acclimated to the prevailing conditions. Multi-omics can be harnessed across temporal and spatial (sub-cellular) dimensions to understand adaptation at the molecular level. Gene deletion libraries, in conjunction with large-scale approaches and evolving bioinformatics integration, will greatly facilitate next-generation vaccines and antimicrobial interventions by highlighting novel targets and pathogen-specific pathways. MS is also central in phenotypic characterization of surface biomolecules such as lipid A, as well as aiding in the determination of protein interactions and complexes. There is increasing evidence that bacteria are capable of widespread post-translational modification, including phosphorylation, glycosylation and acetylation; with each contributing to virulence. This review focuses on the bacterial genotype to phenotype transition and surveys the recent literature showing how the genome can be validated at the proteome, metabolome and lipidome levels to provide an integrated view of organism response to host conditions.

The potential for flower nectar to allow mosquito to mosquito transmission of Francisella tularensis

Francisella tularensis is disseminated in nature by biting arthropods such as mosquitoes. The relationship between mosquitoes and F. tularensis in nature is highly ambiguous, due in part to the fact that mosquitoes have caused significant tularemia outbreaks despite being classified as a mechanical vector of F. tularensis. One possible explanation for mosquitoes being a prominent, yet mechanical vector is that these insects feed on flower nectar between blood meals, allowing for transmission of F. tularensis between mosquitoes. Here, we aimed to assess whether F. tularensis could survive in flower nectar. Moreover, we examined if mosquitoes could interact with or ingest and transmit F. tularensis from one source of nectar to another. F. tularensis exhibited robust survivability in flower nectar with concentrations of viable bacteria remaining consistent with the rich growth medium. Furthermore, F. tularensis was able to survive (albeit to a lesser extent) in 30% sucrose (a nectar surrogate) over a period of time consistent with that of a typical flower bloom. Although we observed diminished bacterial survival in the nectar surrogate, mosquitoes that fed on this material became colonized with F. tularensis. Finally, colonized mosquitoes were capable of transferring F. tularensis to a sterile nectar surrogate. These data suggest that flower nectar may be capable of serving as a temporary source of F. tularensis that could contribute to the amplification of outbreaks. Mosquitoes that feed on an infected mammalian host and subsequently feed on flower nectar could deposit some F. tularensis bacteria into the nectar in the process. Mosquitoes subsequently feeding on this nectar source could potentially become colonized by F. tularensis. Thus, the possibility exists that flower nectar may allow for vector-vector transmission of F. tularensis.

Alarm Odor Compounds of the Brown Marmorated Stink Bug Exhibit Antibacterial Activity

Some insects release scented compounds as a defense against predators that also exhibit antimicrobial activity. Trans-2-octenal and trans-2-decenal are the major alarm aldehydes responsible for the scent of Halyomorpha halys, the brown marmorated stink bug. Previous research has shown these aldehydes are antifungal and produce an antipredatory effect, but have never been tested for antibacterial activity. We hypothesized that these compounds functioned similarly to the analogous multifunctional action of earwig compounds, so we tested whether these aldehydes could inhibit the growth of bacteria. Disk diffusion assays indicated that these aldehydes significantly inhibited the growth of Methicillin-resistant Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, in vitro. Moreover, mealworm beetles (Tenebrio molitor) coated in stink bug aldehydes showed a substantial reduction in bacterial colonization compared to vehicle-treated insects. These results suggest that brown marmorated stinkbug aldehydes are indeed antibacterial agents and serve a multifunctional role for this insect. Therefore, stinkbug aldehydes may have potential for use as chemical antimicrobials.

Functional analysis of N-linking oligosaccharyl transferase enzymes encoded by deep-sea vent proteobacteria

Bacterial N-linking oligosaccharyl transferases (OTase enzymes) transfer lipid-linked glycans to selected proteins in the periplasm and were first described in the intestinal pathogen Campylobacter jejuni, a member of the ε-proteobacteria-subdivision of bacteria. More recently, orthologues from other ε-proteobacterial Campylobacter and Helicobacter species and a δ-proteobacterium, Desulfovibrio desulfuricans, have been described, suggesting that these two subdivisions of bacteria may be a source of further N-linked protein glycosylation systems. Whole-genome sequencing of both ε- and δ-proteobacteria from deep-sea vent habitats, a rich source of species from these subdivisions, revealed putative ORFs encoding OTase enzymes and associated adjacent glycosyltransferases similar to the C. jejuni N-linked glycosylation locus. We expressed putative OTase ORFs from the deep-sea vent species Nitratiruptor tergarcus, Sulfurovum lithotrophicum and Deferribacter desulfuricans in Escherichia coli and showed that they were able to functionally complement the C. jejuni OTase, CjPglB. The enzymes were shown to possess relaxed glycan specificity, transferring diverse glycan structures and demonstrated different glycosylation sequon specificities. Additionally, a permissive D. desulfuricans acceptor protein was identified, and we provide evidence that the N-linked glycan synthesized by N. tergarcus and S. lithotrophicum contains an acetylated sugar at the reducing end. This work demonstrates that deep-sea vent bacteria encode functional N-glycosylation machineries and are a potential source of biotechnologically important OTase enzymes.

Selective distribution of Pseudomonas aeruginosa O-antigen among strains producing group I pilin

Strains of Pseudomonas aeruginosa that produce type IVa pili categorized as group I have the potential to covalently attach an O-antigen repeating unit to the pilin C-terminal residue. PCR, employing primers targeting a conserved region of a group-I-specific gene, was used to provide evidence that 110 of 206 clinical isolates studied had the capability of producing this type of pilus. The potential of P. aeruginosa to produce a particular O-antigen type is determined by the presence of a specific biosynthetic gene cluster. The distribution of these gene clusters among the isolates studied was determined using a second PCR procedure. The results of these studies showed that the O-antigen repeating unit types associated with group I pilin producers were significantly different from those found in the non-group I pilin strains. In addition, the predicted ability to express O-antigen repeating units composed of four sugars, and the ability of the glycan to express a negative charge were associated with group I pilin producing strains. The results presented suggest that these properties specifically enhance group I pilus function and that the commonality of pilus and O-antigen types may be useful as targets in disease intervention.

The group I pilin glycan affects type IVa pilus hydrophobicity and twitching motility in Pseudomonas aeruginosa 1244

The group I pilin category is the most common type of type IVa pilus produced by Pseudomonas aeruginosa. The lateral surfaces of these pili are characterized by the presence of closely spaced, covalently attached O-antigen repeating units. The current work was conducted to investigate the pilin glycan's effect on pilus solubility and function. Culture supernatant fluids containing fully, partially and non-glycosylated P. aeruginosa group I pili were tested for solubility in the presence of ammonium sulfate. These results showed that while pili expressing three or four sugars were highly soluble under all conditions, those with fewer than three were insoluble under the lowest salt concentrations tested. A representative of the P. aeruginosa group II pili also showed low solubility when assayed under these same conditions. Reduced solubility suggested an increased pilus surface hydrophobicity, which was supported by protein modelling. While having no effect on the WT strain, an ionic strength found at many host infection sites inhibited surface and subsurface twitching motility of strain 1244G7, an isogenic mutant unable to glycosylate pilin. This effect was reversed by mutant complementation. Twitching motility of P. aeruginosa strain PA103, which produces group II pili, was also inhibited by ionic strengths which influenced the mutant 1244 strain. We suggest that the group I pilin glycan may, therefore, be beneficial to this organism specifically for optimal pilus functioning at the many host disease sites with ionic strengths comparable to those tested here.

The sweet tooth of bacteria: common themes in bacterial glycoconjugates

Humans have been increasingly recognized as being superorganisms, living in close contact with a microbiota on all their mucosal surfaces. However, most studies on the human microbiota have focused on gaining comprehensive insights into the composition of the microbiota under different health conditions (e.g., enterotypes), while there is also a need for detailed knowledge of the different molecules that mediate interactions with the host. Glycoconjugates are an interesting class of molecules for detailed studies, as they form a strain-specific barcode on the surface of bacteria, mediating specific interactions with the host. Strikingly, most glycoconjugates are synthesized by similar biosynthesis mechanisms. Bacteria can produce their major glycoconjugates by using a sequential or an en bloc mechanism, with both mechanistic options coexisting in many species for different macromolecules. In this review, these common themes are conceptualized and illustrated for all major classes of known bacterial glycoconjugates, with a special focus on the rather recently emergent field of glycosylated proteins. We describe the biosynthesis and importance of glycoconjugates in both pathogenic and beneficial bacteria and in both Gram-positive and -negative organisms. The focus lies on microorganisms important for human physiology. In addition, the potential for a better knowledge of bacterial glycoconjugates in the emerging field of glycoengineering and other perspectives is discussed.

Pilin Processing Follows a Different Temporal Route than That of Archaellins in Methanococcus maripaludis

Methanococcus maripaludis has two different surface appendages: type IV-like pili and archaella. Both structures are believed to be assembled using a bacterial type IV pilus mechanism. Each structure is composed of multiple subunits, either pilins or archaellins. Both pilins and archaellins are made initially as preproteins with type IV pilin-like signal peptides, which must be removed by a prepilin peptidase-like enzyme. This enzyme is FlaK for archaellins and EppA for pilins. In addition, both pilins and archaellins are modified with N-linked glycans. The archaellins possess an N-linked tetrasaccharide while the pilins have a pentasaccharide which consists of the archaellin tetrasaccharide but with an additional sugar, an unidentified hexose, attached to the linking sugar. In this report, we show that archaellins can be processed by FlaK in the absence of N-glycosylation and N-glycosylation can occur on archaellins that still retain their signal peptides. In contrast, pilins are not glycosylated unless they have been acted on by EppA to have the signal peptide removed. However, EppA can still remove signal peptides from non-glycosylated pilins. These findings indicate that there is a difference in the order of the posttranslational modifications of pilins and archaellins even though both are type IV pilin-like proteins.

Aeromonas hydrophila flagella glycosylation: involvement of a lipid carrier

Polar flagellin proteins from Aeromonas hydrophila strain AH-3 (serotype O34) were found to be O-glycosylated with a heterogeneous glycan. Mutants unable to produce WecP or Gne enzymes showed altered motility, and the study of their polar flagellin glycosylation showed that the patterns of glycosylation differed from that observed with wild type polar flagellin. This suggested the involvement of a lipid carrier in glycosylation. A gene coding for an enzyme linking sugar to a lipid carrier was identified in strain AH-3 (WecX) and subsequent mutation abolished completely motility, flagella production by EM, and flagellin glycosylation. This is the first report of a lipid carrier involved in flagella O-glycosylation. A molecular model has been proposed. The results obtained suggested that the N-acetylhexosamines are N-acetylgalactosamines and that the heptasaccharide is completely independent of the O34-antigen lipopolysaccharide. Furthermore, by comparing the mutants with differing degrees of polar flagellin glycosylation, we established their importance in A. hydrophila flagella formation and motility.

Type IV pilin proteins: versatile molecular modules

Type IV pili (T4P) are multifunctional protein fibers produced on the surfaces of a wide variety of bacteria and archaea. The major subunit of T4P is the type IV pilin, and structurally related proteins are found as components of the type II secretion (T2S) system, where they are called pseudopilins; of DNA uptake/competence systems in both Gram-negative and Gram-positive species; and of flagella, pili, and sugar-binding systems in the archaea. This broad distribution of a single protein family implies both a common evolutionary origin and a highly adaptable functional plan. The type IV pilin is a remarkably versatile architectural module that has been adopted widely for a variety of functions, including motility, attachment to chemically diverse surfaces, electrical conductance, acquisition of DNA, and secretion of a broad range of structurally distinct protein substrates. In this review, we consider recent advances in this research area, from structural revelations to insights into diversity, posttranslational modifications, regulation, and function.

Glycosylation of pilin and nonpilin protein constructs by Pseudomonas aeruginosa 1244

PilO is an oligosaccharyl transferase (OTase) that catalyzes the O-glycosylation of Pseudomonas aeruginosa 1244 pilin by adding a single O-antigen repeating unit to the β carbon of the C-terminal residue (a serine). While PilO has an absolute requirement for Ser/Thr at this position, it is unclear if this enzyme must recognize other pilin features. To test this, pilin constructs containing peptide extensions terminating with serine were tested for the ability to support glycosylation. It was found that a 15-residue peptide, which had been modeled on the C-proximal region of strain 1244 pilin, served as a PilO substrate when it was expressed on either group II or group III pilins. In addition, adding a 3-residue extension culminating in serine to the C terminus of a group III pilin supported PilO activity. A protein fusion composed of strain 1244 pilin linked at its C terminus with Escherichia coli alkaline phosphatase (which, in turn, contained the above-mentioned 15 amino acids at its C terminus) was glycosylated by PilO. E. coli alkaline phosphatase lacking the pilin membrane anchor and containing the 15-residue peptide was also glycosylated by PilO. Addition of the 3-residue extension did not allow glycosylation of either of these constructs. Site-directed mutagenesis of strain 1244 pilin residues of the C-proximal region common to the group I proteins showed that this structure was not required for glycosylation. These experiments indicate that pilin common sequence is not required for glycosylation and show that nonpilin protein can be engineered to be a PilO substrate.

Global transcriptional response to mammalian temperature provides new insight into Francisella tularensis pathogenesis

Background

After infecting a mammalian host, the facultative intracellular bacterium, Francisella tularensis, encounters an elevated environmental temperature. We hypothesized that this temperature change may regulate genes essential for infection.

Results

Microarray analysis of F. tularensis LVS shifted from 26°C (environmental) to 37°C (mammalian) showed ~11% of this bacterium's genes were differentially-regulated. Importantly, 40% of the protein-coding genes that were induced at 37°C have been previously implicated in virulence or intracellular growth of Francisella in other studies, associating the bacterial response to this temperature shift with pathogenesis. Forty-four percent of the genes induced at 37°C encode proteins of unknown function, suggesting novel Francisella virulence traits are regulated by mammalian temperature. To explore this possibility, we generated two mutants of loci induced at 37°C [FTL_1581 and FTL_1664 (deoB)]. The FTL_1581 mutant was attenuated in a chicken embryo infection model, which was likely attributable to a defect in survival within macrophages. FTL_1581 encodes a novel hypothetical protein that we suggest naming temperature-induced, virulence-associated locus A, tivA. Interestingly, the deoB mutant showed diminished entry into mammalian cells compared to wild-type LVS, including primary human macrophages and dendritic cells, the macrophage-like RAW 264.7 line, and non-phagocytic HEK-293 cells. This is the first study identifying a Francisella gene that contributes to uptake into both phagocytic and non-phagocytic host cells.

Conclusion

Our results provide new insight into mechanisms of Francisella virulence regulation and pathogenesis. F. tularensis LVS undergoes considerable gene expression changes in response to mammalian body temperature. This temperature shift is important for the regulation of genes that are critical for the pathogenesis of Francisella. Importantly, the compilation of temperature-regulated genes also defines a rich collection of novel candidate virulence determinants, including tivA (FTL_1581). An analysis of tivA and deoB (FTL_1664) revealed that these genes contribute to intracellular survival and entry into mammalian cells, respectively.

Modification of Pseudomonas aeruginosa Pa5196 type IV Pilins at multiple sites with D-Araf by a novel GT-C family Arabinosyltransferase, TfpW

Pseudomonas aeruginosa Pa5196 produces type IV pilins modified with unusual alpha1,5-linked d-arabinofuranose (alpha1,5-D-Araf) glycans, identical to those in the lipoarabinomannan and arabinogalactan cell wall polymers from Mycobacterium spp. In this work, we identify a second strain of P. aeruginosa, PA7, capable of expressing arabinosylated pilins and use a combination of site-directed mutagenesis, electrospray ionization mass spectrometry (MS), and electron transfer dissociation MS to identify the exact sites and extent of pilin modification in strain Pa5196. Unlike previously characterized type IV pilins that are glycosylated at a single position, those from strain Pa5196 were modified at multiple sites, with modifications of alphabeta-loop residues Thr64 and Thr66 being important for normal pilus assembly. Trisaccharides of alpha1,5-D-Araf were the principal modifications at Thr64 and Thr66, with additional mono- and disaccharides identified on Ser residues within the antiparallel beta sheet region of the pilin. TfpW was hypothesized to encode the pilin glycosyltransferase based on its genetic linkage to the pilin, weak similarity to membrane-bound GT-C family glycosyltransferases (which include the Mycobacterium arabinosyltransferases EmbA/B/C), and the presence of characteristic motifs. Loss of TfpW or mutation of key residues within the signature GT-C glycosyltransferase motif completely abrogated pilin glycosylation, confirming its involvement in this process. A Pa5196 pilA mutant complemented with other Pseudomonas pilins containing potential sites of modification expressed nonglycosylated pilins, showing that TfpW's pilin substrate specificity is restricted. TfpW is the prototype of a new type IV pilin posttranslational modification system and the first reported gram-negative member of the GT-C glycosyltransferase family.

Not just for Eukarya anymore: protein glycosylation in Bacteria and Archaea

Of the many post-translational modifications proteins can undergo, glycosylation is the most prevalent and the most diverse. Today, it is clear that both N-glycosylation and O-glycosylation, once believed to be restricted to eukaryotes, also transpire in Bacteria and Archaea. Indeed, prokaryotic glycoproteins rely on a wider variety of monosaccharide constituents than do those of eukaryotes. In recent years, substantial progress in describing the enzymes involved in bacterial and archaeal glycosylation pathways has been made. It is becoming clear that enhanced knowledge of bacterial glycosylation enzymes may be of therapeutic value, while the demonstrated ability to introduce bacterial glycosylation genes into Escherichia coli represents a major step forward in glyco-engineering. A better understanding of archaeal protein glycosylation provides insight into this post-translational modification across evolution as well as protein processing under extreme conditions. Here, we discuss new structural and biosynthetic findings related to prokaryotic protein glycosylation, until recently a neglected topic.

Affinity-capture tandem mass spectrometric characterization of polyprenyl-linked oligosaccharides: tool to study protein N-glycosylation pathways

N-glycosylation of proteins is recognized as one of the most common post-translational modifications. Until recently it was believed that N-glycosylation occurred exclusively in eukaryotes before the discovery of the general protein glycosylation pathway (Pgl) in Campylobacter jejuni. To date, most techniques to analyze lipid-linked oligosaccharides (LLOs) of these pathways involve the use of radiolabels and chromatographic separation. Technologies capable of characterizing eukaryotic and the newly described bacterial N-glycosylation systems from biologically relevant samples in a quick, accurate, and cost-effective manner are needed. In this paper a new glycomics strategy based on lectin-affinity capture was devised and validated on the C. jejuni N-glycan pathway and the engineered Escherichia coli strains expressing the functional C. jejuni pathway. The lipid-linked oligosaccharide intermediates of the Pgl pathway were then enriched using SBA-agarose affinity-capture and examined by capillary electrophoresis-mass spectrometry (CE-MS). We demonstrate that this method is capable of detecting low levels of LLOs, the sugars are indeed assembled on undecaprenylpyrophosphate, and structural information for expected and unexpected LLOs can be obtained without further sample manipulation. Furthermore, CE-MS analyses of C. jejuni and the E. coli "glyco-factories" showed striking differences in the assembly and control of N-glycan biosynthesis.

Immunization with a Pseudomonas aeruginosa 1244 pilin provides O-antigen-specific protection

The O antigen is both a major structural outer membrane component and the dominant epitope of most gram-negative bacteria. Pseudomonas aeruginosa 1244 produces a type IV pilus and covalently links an O-antigen repeating unit to each pilin monomer. Here we show that immunization of mice with pure pilin from strain 1244 by use of either the mouse respiratory model or the thermal injury model resulted in protection from challenge with a pilus-null O-antigen-producing 1244 mutant. These results provide evidence that the pilin glycan stimulates a protective response that targets the O antigen, suggesting that this system could be used as the basis for the development of a variety of bioconjugate vaccines protective against gram-negative bacteria.

PilO of Pseudomonas aeruginosa 1244: subcellular location and domain assignment

PilO of Pseudomonas aeruginosa 1244 catalyses the attachment of an O-antigen repeating unit to the beta-carbon of the pilin C-terminal residue, a serine. The present study was conducted to locate the regions of this enzyme important in catalysis and to establish the cellular location of the pilin glycosylation reaction. While PilO was not detectable in extracts of P. aeruginosa or Escherichia coli, even under conditions of overexpression, it was found that an intact MalE-PilO fusion protein was produced in significant amounts. This fusion complemented a P. aeruginosa 1244 mutant containing a pilO deletion and targeted to the cytoplasmic membrane of E. coli. Wzy and WaaL, enzymes that also utilize the O-antigen repeating unit as substrate, were found to share a sequence pattern with PilO even though these proteins have little overall sequence similarity. PilO constructs in which portions of this common sequence were deleted or altered by site-directed mutagenesis lacked pilin glycosylating activity. Deletions of segments downstream from the common region also prevented enzyme activity. Topology studies showed that the two PilO regions associated with enzyme activity were located in the periplasm. These results establish regions of this enzyme important for catalysis and present evidence that pilin glycosylation occurs in the periplasmic space of this organism.

Glycosylation of Pseudomonas aeruginosa strain Pa5196 type IV pilins with mycobacterium-like alpha-1,5-linked d-Araf oligosaccharides

Pseudomonas aeruginosa is a gram-negative bacterium that uses polar type IV pili for adherence to various materials and for rapid colonization of surfaces via twitching motility. Within the P. aeruginosa species, five distinct alleles encoding variants of the structural subunit PilA varying in amino acid sequence, length, and presence of posttranslational modifications have been identified. In this work, a combination of mass spectrometry and nuclear magnetic resonance spectroscopy was used to identify a novel glycan modification on the pilins of the group IV strain Pa5196. Group IV pilins continued to be modified in a lipopolysaccharide (wbpM) mutant of Pa5196, showing that, unlike group I strains, the pilins of group IV are not modified with the O-antigen unit of the background strain. Instead, the pilin glycan was determined to be an unusual homo-oligomer of alpha-1,5-linked d-arabinofuranose (d-Araf). This sugar is uncommon in prokaryotes, occurring mainly in the cell wall arabinogalactan and lipoarabinomannan (LAM) polymers of mycobacteria, including Mycobacterium tuberculosis and Mycobacterium leprae. Antibodies raised against M. tuberculosis LAM specifically identified the glycosylated pilins from Pa5196, confirming that the glycan is antigenically, as well as chemically, identical to those of Mycobacterium. P. aeruginosa Pa5196, a rapidly growing strain of low virulence that expresses large amounts of glycosylated type IV pilins on its surface, represents a genetically tractable model system for elucidation of alternate pathways for biosynthesis of d-Araf and its polymerization into mycobacterium-like alpha-1,5-linked oligosaccharides.

Flagellar glycosylation - a new component of the motility repertoire?

The biosynthesis, assembly and regulation of the flagellar apparatus has been the subject of extensive studies over many decades, with considerable attention devoted to the peritrichous flagella of Escherichia coli and Salmonella enterica. The characterization of flagellar systems from many other bacterial species has revealed subtle yet distinct differences in composition, regulation and mode of assembly of this important subcellular structure. Glycosylation of the major structural protein, the flagellin, has been shown most recently to be an important component of numerous flagellar systems in both Archaea and Bacteria, playing either an integral role in assembly or for a number of bacterial pathogens a role in virulence. This review focuses on the structural diversity in flagellar glycosylation systems and demonstrates that as a consequence of the unique assembly processes, the type of glycosidic linkage found on archaeal and bacterial flagellins is distinctive.

Pseudomonas aeruginosa 1244 pilin glycosylation: glycan substrate recognition

The pilin of Pseudomonas aeruginosa 1244 is glycosylated with an oligosaccharide that is structurally identical to the O-antigen repeating unit of this organism. Concordantly, the metabolic source of the pilin glycan is the O-antigen biosynthetic pathway. The present study was conducted to investigate glycan substrate recognition in the 1244 pilin glycosylation reaction. Comparative structural analysis of O subunits that had been previously shown to be compatible with the 1244 glycosylation machinery revealed similarities among sugars at the presumed reducing termini of these oligosaccharides. We therefore hypothesized that the glycosylation substrate was within the sugar at the reducing end of the glycan precursor. Since much is known of PA103 O-antigen genetics and because the sugars at the reducing termini of the O7 (strain 1244) and O11 (strain PA103) are identical (beta-N-acetyl fucosamine), we utilized PA103 and strains that express lipopolysaccharide (LPS) with a truncated O-antigen subunit to test our hypothesis. LPS from a strain mutated in the wbjE gene produced an incomplete O subunit, consisting only of the monosaccharide at the reducing end (beta-d-N-acetyl fucosamine), indicating that this moiety contained substrate recognition elements for WaaL. Expression of pilAO(1244) in PA103 wbjE::aacC1, followed by Western blotting of extracts of these cells, indicated that pilin produced has been modified by the addition of material consistent with a single N-acetyl fucosamine. This was confirmed by analyzing endopeptidase-treated pilin by mass spectrometry. These data suggest that the pilin glycosylation substrate recognition features lie within the reducing-end moiety of the O repeat and that structures of the remaining sugars are irrelevant.