Nikolay Paramonov

Identification of a Second Lipopolysaccharide in Porphyromonas gingivalis W50

We previously described a cell surface anionic polysaccharide (APS) in Porphyromonas gingivalis that is required for cell integrity and serum resistance. APS is a phosphorylated branched mannan that shares a common epitope with posttranslational additions to some of the Arg-gingipains. This study aimed to determine the mechanism of anchoring of APS to the surface of P. gingivalis. APS was purified on concanavalin A affinity columns to minimize the loss of the anchoring system that occurred during chemical extraction. (1)H nuclear magnetic resonance spectroscopy of the lectin-purified APS confirmed the previous structure but also revealed additional signals that suggested the presence of a lipid A. This was confirmed by fatty acid analysis of the APS and matrix-assisted laser desorption ionization-time of flight mass spectrometry of the lipid A released by treatment with sodium acetate buffer (pH 4.5). Hence, P. gingivalis synthesizes two distinct lipopolysaccharide (LPS) macromolecules containing different glycan repeating units: O-LPS (with O-antigen tetrasaccharide repeating units) and A-LPS (with APS repeating units). Nonphosphorylated penta-acylated and nonphosphorylated tetra-acylated species were detected in lipid A from P. gingivalis total LPS and in lipid A from A-LPS. These lipid A species were unique to lipid A derived from A-LPS. Biological assays demonstrated a reduced proinflammatory activity of A-LPS compared to that of total LPS. Inactivation of a putative O-antigen ligase (waaL) at PG1051, which is required for the final step of LPS biosynthesis, abolished the linkage of both the O antigen and APS to the lipid A core of O-LPS and A-LPS, respectively, suggesting that WaaL in P. gingivalis has dual specificity for both O-antigen and APS repeating units.

Structural analysis of a novel anionic polysaccharide from Porphyromonas gingivalis strain W50 related to Arg-gingipain glycans

The Arg‐gingipains (RgpsA and B) of Porphyromonas gingivalis are a family of extracellular cysteine proteases and are important virulence determinants of this periodontal bacterium. A monoclonal antibody, MAb1B5, which recognizes an epitope on glycosylated monomeric RgpAs also cross‐reacts with a cell‐surface polysaccharide of P. gingivalis W50 suggesting that the maturation pathway of the Arg‐gingipains may be linked to the biosynthesis of a surface carbohydrate. We report the purification and structural characterization of the cross‐reacting anionic polysaccharide (APS), which is distinct from both the lipopolysaccharide and serotype capsule polysaccharide of P. gingivalis W50. The structure of APS was determined by 1D and 2D NMR spectroscopy and methylation analysis, which showed it to be a phosphorylated branched mannan. The backbone is built up of α‐1,6‐linked mannose residues and the side‐chains contain α‐1,2‐linked mannose oligosaccharides of different lengths (one to two sugar residues) attached to the backbone via 1,2‐linkage. One of the side‐chains in the repeating unit contains Manα1‐2Manα1‐phosphate linked via phosphorus to a backbone mannose at position 2. De‐O‐phosphorylation of APS abolished cross‐reactivity suggesting that Manα1‐2Manα1‐phosphate fragment forms part of the epitope recognized by MAb1B5. This phosphorylated branched mannan represents a novel polysaccharide that is immunologically related to the post‐translational additions of Arg‐gingipains.

Glycosylation of immunoglobulin light chains associated with amyloidosis

AL amyloidosis is a fatal disease caused by deposition of immunoglobulin light chains in a fibrillar form (AL) in various organs. By searching the Kabat database of immunoglobulin sequences using the KabatMan software, we have shown that there is a preponderance of the consensus glycosylation sequon (AsnXxxSer/Thr) in the framework regions of amyloid light chains. We have characterised by computer graphics simulations, NMR spectroscopy and carbohydrate biochemistry the structure and conformation of the oligosaccharide from amyloid protein AL MS (λI) and from the amyloid associated Bence Jones protein of patient MH (K1). These proteins have glycosylation in the hypervariable complementarity–determining region versus framework region, respectively. Both contained a 2–6 sialylated core fucosylated biantennary chain mostly with bisecting GlcNAc. Together our results suggest that light chain glycosylation may be one of several modifications which may render the protein more prone to amyloid formation.

Expression of Arg-Gingipain RgpB Is Required for Correct Glycosylation and Stability of Monomeric Arg-Gingipain RgpA from Porphyromonas gingivalis W50

ABSTRACT Arg-gingipains are extracellular cysteine proteases produced by the gram-negative periodontal pathogen Porphyromonas gingivalis and are encoded by rgpA and rgpB. Three Arg-gingipains, heterodimeric high-molecular-mass Arg-gingipain HRgpA comprising the α-catalytic chain and the β-adhesin chain, the monomeric soluble Arg-gingipain comprising only the α-catalytic chain (RgpAcat), and the monomeric membrane-type heavily glycosylated Arg-gingipain comprising the α-catalytic chain (mt-RgPAcat), are derived from rgpA. The monomeric enzymes contain between 14 and 30% carbohydrate by weight. rgpB encodes two monomeric enzymes, RgpB and mt-RgpB. Earlier work indicated that rgpB is involved in the glycosylation process, since inactivation of rgpB results in the loss of not only RgpB and mt-RgpB but also mt-RgpAcat. This work aims to confirm the role of RgpB in the posttranslational modification of RgpAcat and the effect of aberrant glycosylation on the properties of this enzyme. Two-dimensional gel electrophoresis of cellular proteins from W50 and an inactivated rgpB strain (D7) showed few differences, suggesting that loss of RgpB has a specific effect on RgpA maturation. Inactivation of genes immediately upstream and downstream of rgpB had no effect on rgpA-derived enzymes, suggesting that the phenotype of the rgpB mutant is not due to a polar effect on transcription at this locus. Matrix-assisted laser desorption ionization-time of flight analysis of purified RgpAcat from W50 and D7 strains gave identical peptide mass fingerprints, suggesting that they have identical polypeptide chains. However, RgpAcat from D7 strain had a higher isoelectric point and a dramatic decrease in thermostability and did not cross-react with a monoclonal antibody which recognizes a glycan epitope on the parent strain enzyme. Although it had the same total sugar content as the parent strain enzyme, there were significant differences in the monosaccharide composition and linking sugars. These data suggest that RgpB is required for the normal posttranslational glycosylation of Arg-gingipains derived from rgpA and that this process is required for enzyme stabilization.

Characterization of the α- and β-mannosidases of Porphyromonas gingivalis.

Mannose is an important sugar in the biology of the Gram-negative bacterium Porphyromonas gingivalis. It is a major component of the oligosaccharides attached to the Arg-gingipain cysteine proteases, the repeating units of an acidic lipopolysaccharide (A-LPS), and the core regions of both types of LPS produced by the organism (O-LPS and A-LPS) and a reported extracellular polysaccharide (EPS) isolated from spent culture medium. The organism occurs at inflamed sites in periodontal tissues, where it is exposed to host glycoproteins rich in mannose, which may be substrates for the acquisition of mannose by P. gingivalis. Five potential mannosidases were identified in the P. gingivalis W83 genome that may play a role in mannose acquisition. Four mannosidases were characterized in this study: PG0032 was a β-mannosidase, whereas PG0902 and PG1712 were capable of hydrolyzing p-nitrophenyl α-d-mannopyranoside. PG1711 and PG1712 were α-1 → 3 and α-1 → 2 mannosidases, respectively. No enzyme function could be assigned to PG0973. α-1 → 6 mannobiose was not hydrolyzed by P. gingivalis W50. EPS present in the culture supernatant was shown to be identical to yeast mannan and a component of the medium used for culturing P. gingivalis and was resistant to hydrolysis by mannosidases. Synthesis of O-LPS and A-LPS and glycosylation of the gingipains appeared to be unaffected in all mutants. Thus, α- and β-mannosidases of P. gingivalis are not involved in the harnessing of mannan/mannose from the growth medium for these biosynthetic processes. P. gingivalis grown in chemically defined medium devoid of carbohydrate showed reduced α-mannosidase activity (25%), suggesting these enzymes are environmentally regulated.

Hemin binding by Porphyromonas gingivalis strains is dependent on the presence of A-LPS

Porphyromonas gingivalis is a Gram‐negative black pigmenting anaerobe that is unable to synthesize heme [Fe(II)‐protoporphyrin IX] or hemin [Fe(III)‐protoporphyrin IX‐Cl], which are important growth/virulence factors, and must therefore derive them from the host. Porphyromonas gingivalis expresses several proteinaceous hemin‐binding sites, which are important in the binding/transport of heme/hemin from the host. It also synthesizes several virulence factors, namely cysteine‐proteases Arg‐ and Lys‐gingipains and two lipopolysaccharides (LPS), O‐LPS and A‐LPS. The gingipains are required for the production of the black pigment, μ‐oxo‐bisheme {[Fe(III)PPIX]2 O}, which is derived from hemoglobin and deposited on the bacterial cell‐surface leading to the characteristic black colonies when grown on blood agar. In this study we investigated the role of LPS in the deposition of μ‐oxo‐bisheme on the cell‐surface. A P. gingivalis mutant defective in the biosynthesis of Arg‐gingipains, namely rgpA/rgpB, produces brown colonies on blood agar and mutants defective in Lys‐gingipain (kgp) and LPS biosynthesis namely porR, waaL, wzy, and pg0129 (α‐1, 3‐mannosyltransferase) produce non‐pigmented colonies. However, only those mutants lacking A‐LPS showed reduced hemin‐binding when cells in suspension were incubated with hemin. Using native, de‐O‐phosphorylated and de‐lipidated LPS from P. gingivalis W50 and porR strains, we demonstrated that hemin‐binding to O‐polysaccharide (PS) and to the lipid A moiety of LPS was reduced compared with hemin‐binding to A‐PS. We conclude that A‐LPS in the outer‐membrane of P. gingivalis serves as a scaffold/anchor for the retention of μ‐oxo‐bisheme on the cell surface and pigmentation is dependent on the presence of A‐LPS.

Generation and characterisation of Porphyromonas gingivalis mutant lacking peptidylarginine deiminase activity

ABSTRACT Porphyromonas gingivalis peptidylarginine deiminase (PPAD) is the focus of several studies due to its ability to citrullinate in vitro human proteins, which have been linked to the aetiopathogenesis of rheumatoid arthritis (RA). The aim of this work was the generation by homologous recombination and characterisation of a P. gingivalis W50 mutant lacking pad gene (PG1424) to study the role of PPAD in RA. To confirm the absence of PPAD activity in P. gingivalis PG1424, cells were incubated with arginine-containing substrates and citrullination of L-arginine measured using a colorimetric assay and thin-layer chromatography. Furthermore, arginine and lysine protease (gingipain) activities were assessed and immunoblotting was performed using monoclonal antibody 1B5 (mAb1B5) and a commercial anti-modified citrulline antibody (AMC) to detect differences in virulence factor expression. The deletion of pad gene in P. gingivalis PG1424 completely abolished the ability to autocitrullinate P. gingivalis proteins in the mutant strain and also the citrullination of used substrates but not free L-arginine. Moreover, the wild-type and mutant strains had similar total gingipain activities and reactivity with mAb1B5. In conclusion, this work has produced a well-characterised PPAD-deleted P. gingivalis strain, which can be used to help determine the role of citrullination by this microorganism in RA.

Cardiolipins Act as a Selective Barrier to Toll-Like Receptor 4 Activation in the Intestine

ABSTRACT Intestinal homeostasis mechanisms must protect the host intestinal tissue from endogenous lipopolysaccharides (LPSs) produced by the intestinal microbiota. In this report, we demonstrate that murine intestinal fecal lipids effectively block Toll-like receptor 4 (TLR4) responses to naturally occurring Bacteroidetes sp. LPS. Cardiolipin (CL) represents a significant proportion of the total intestinal and fecal lipids and, furthermore, potently antagonizes TLR4 activation by reducing LPS binding at the lipopolysaccharide binding protein (LBP), CD14, and MD-2 steps of the TLR4 signaling pathway. It is further demonstrated that intestinal lipids and CL are less effective at neutralizing more potent Enterobacteriaceae-type LPS, which is enriched in feces obtained from mice with dextran sodium sulfate (DSS)-treated inflammatory bowel disease. The selective inhibition of naturally occurring LPS structures by intestinal lipids may represent a novel homeostasis mechanism that blocks LPS activation in response to symbiotic but not dysbiotic microbial communities. IMPORTANCE The guts of animals harbor a variety of Gram-negative bacteria associated with both states of intestinal health and states of disease. Environmental factors, such as dietary habits, can drive the microbial composition of the host animals intestinal bacterial community toward a more pathogenic state. Both beneficial and harmful Gram-negative bacteria are capable of eliciting potentially damaging inflammatory responses from the host intestinal tissues via a lipopolysaccharide (LPS)-dependent pathway. Physical mucosal barriers and antibodies produced by the intestinal immune system protect against the undesired inflammatory effects of LPS, although it is unknown why some bacteria are more effective at overcoming the protective barriers than others. This report describes the discovery of a lipid-type protective barrier in the intestine that reduces the deleterious effects of LPSs from beneficial bacteria but is less effective in dampening the inflammatory effects of LPSs from harmful bacteria, providing a novel mechanistic insight into inflammatory intestinal disorders.