Biosynthesis of D-alanyl-lipoteichoic acid: characterization of ester-linked D-alanine in the in vitro-synthesized product

Lactobacillus casei extracellular vesicles stimulate EGFR pathway likely due to the presence of proteins P40 and P75 bound to their surface

In the complex interplay of beneficial bacteria with the host, there are few examples of bacterial metabolites and effector molecules that have been consistently identified. Protective effects on the intestinal epithelium have been ascribed to P40 and P75, two well characterized cell wall muramidases, present in the culture supernatant of strains belonging to the taxon Lactobacillus casei/paracasei/rhamnosus. This work reports that Lactobacillus casei BL23 extracellular vesicles (BL23 EVs) have a small size (17–20 nm or 24–32 nm, depending on the method used) and contain lipoteichoic acid (LTA). Interestingly, all detected P40 and most of P75 were associated to EVs and possibly located at their external surface, as shown by proteinase K digestion. Biosensor assays showed that both proteins bind LTA and vesicles, suggesting that they could bind to ligands like LTA present on BL23 EVs. Native BL23 EVs have a moderate proinflammatory effect and they were able to induce phosphorylation of the epidermal growth factor receptor (EGFR), showing an effect similar to purified P40 and P75 and leading to the conclusion that the activity described in the supernatant (postbiotic) of these bacteria would be mainly due to P40 and P75 bound to EVs.

Phosphoglycerol-type wall and lipoteichoic acids are enantiomeric polymers differentiated by the stereospecific glycerophosphodiesterase GlpQ

The cell envelope of Gram-positive bacteria generally comprises two types of polyanionic polymers linked to either peptidoglycan (wall teichoic acids; WTA) or to membrane glycolipids (lipoteichoic acids; LTA). In some bacteria, including Bacillus subtilis strain 168, both WTA and LTA are glycerolphosphate polymers yet are synthesized through different pathways and have distinct but incompletely understood morphogenetic functions during cell elongation and division. We show here that the exolytic sn-glycerol-3-phosphodiesterase GlpQ can discriminate between B. subtilis WTA and LTA. GlpQ completely degraded unsubstituted WTA, which lacks substituents at the glycerol residues, by sequentially removing glycerolphosphates from the free end of the polymer up to the peptidoglycan linker. In contrast, GlpQ could not degrade unsubstituted LTA unless it was partially precleaved, allowing access of GlpQ to the other end of the polymer, which, in the intact molecule, is protected by a connection to the lipid anchor. Differences in stereochemistry between WTA and LTA have been suggested previously on the basis of differences in their biosynthetic precursors and chemical degradation products. The differential cleavage of WTA and LTA by GlpQ reported here represents the first direct evidence that they are enantiomeric polymers: WTA is made of sn-glycerol-3-phosphate, and LTA is made of sn-glycerol-1-phosphate. Their distinct stereochemistries reflect the dissimilar physiological and immunogenic properties of WTA and LTA. It also enables differential degradation of the two polymers within the same envelope compartment in vivo, particularly under phosphate-limiting conditions, when B. subtilis specifically degrades WTA and replaces it with phosphate-free teichuronic acids.

Profiling and tandem mass spectrometry analysis of aminoacylated phospholipids in Bacillus subtilis

Cationic modulation of the dominantly negative electrostatic structure of phospholipids plays an important role in bacterial response to changes in the environment. In addition to zwitterionic phosphatidylethanolamine, Gram-positive bacteria are also abundant in positively charged lysyl-phosphatidylglycerol. Increased amounts of both types of lipids render Gram-positive bacterial cells more resistant to cationic antibiotic peptides such as defensins.  Lysyl and alanyl-phosphatidylglycerol as well as alanyl-cardiolipin have also been studied by mass spectroscopy. Phospholipids modified by other amino acids have been discovered by chemical analysis of the lipid lysate but have yet to be studied by mass spectroscopy. We exploited the high sensitivity of modern mass spectroscopy in searching for substructures in complex mixtures to establish a sensitive and thorough screen for aminoacylated phospholipids. The search for deprotonated aminoacyl anions in lipid extracted from Bacillus subtilis strain 168 yielded strong evidence as well as relative abundance of aminoacyl-phosphatidylglycerols, which serves as a crude measure of the specificity of aminoacyl-phosphatidylglycerol synthase MprF. No aminoacyl-cardiolipin was found. More importantly, the second most abundant species in this category is D-alanyl-phosphatidylglycerol, suggesting a possible role in the D-alanylation pathway of wall- and lipo-teichoic acids.

Synthesis of glycerol phosphate lipoteichoic acid in Staphylococcus aureus

Lipoteichoic acid (LTA), a glycerol phosphate surface polymer, is a component of the envelope of Gram-positive bacteria. However, the molecular basis for its synthesis or function is not known. Here we report that Staphylococcus aureus LtaS synthesizes glycerol phosphate LTA. Construction of a mutant S. aureus strain with inducible ltaS expression revealed that LTA synthesis is required for bacterial growth and cell division. An ltaS homologue of Bacillus subtilis restored LTA synthesis and the growth of ltaS mutant staphylococci. Thus, LtaS inhibition can be used as a target to treat human infections caused by antibiotic-resistant S. aureus or other bacterial pathogens.

Antibody response to actinomyces antigen and dental caries experience: implications for caries susceptibility

Fluoridated dentifrices reduce dental caries in subjects who perform effective oral hygiene. Actinomyces naeslundii increases in teeth-adherent microbial biofilms (plaques) in these subjects, and a well-characterized serum immunoglobulin G (IgG) antibody response (Actinomyces antibody [A-Ab]) is also increased. Other studies suggest that a serum IgG antibody response to streptococcal d-alanyl poly(glycerophosphate) (S-Ab) may indicate caries experience associated strongly with gingival health and exposure to fluoridated water. The aim of this study was to investigate relationships between A-Ab response, oral hygiene, S-Ab response, and caries experience. Measurements were made of A-Ab and S-Ab concentrations, caries experience (number of decayed, missing, and filled teeth [DMFT], number of teeth surfaces [DMFS], and number of decayed teeth needing treated [DT]), exposure to fluoridated water (Flu), mean clinical pocket depth (PD; in millimeters), and extent of plaque (PL) and gingival bleeding on probing (BOP). A-Ab concentration, the dependent variable in a multiple regression analysis, increased with S-Ab concentration and decreased with PL and DMFT adjusted for Flu (R(2) = 0.51, P < 0.002). Residual associations with age, DMFS, DT, and BOP were not significant. In addition, an elevated A-Ab response, defined from immunoprecipitation and immunoassay measurements, indicated a significant, 30% reduction in DMFT after adjustment for significant age and Flu covariance (analysis of variance with covariance F statistic = 10.6, P < 0.003; S-Ab response and interactions not significant). Thus, an elevated A-Ab response indicates less caries in subjects performing effective oral hygiene using fluoridated dentifrices. Conversely, a low A-Ab response is suggestive of decreased A. naeslundii binding to saliva-coated apatite and greater caries experience, as reported by others.

A continuum of anionic charge: structures and functions of D-alanyl-teichoic acids in gram-positive bacteria

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and D-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with D-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of D-alanyl-TAs, the D-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of D-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of D-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to D-alanyl-TA synthesis.

Antibody-based diagnostic for 'refractory' periodontitis

OBJECTIVE

About 10-15% of US adults are 'refractory' to therapy for chronic periodontitis. Recently, studies suggest that these patients have elevated lysine decarboxylase activity in the sulcular microbiota. The aim of this study was to determine whether an elevated IgG antibody response to lysine decarboxylase, alone or with antibody to other bacterial antigens and baseline clinical measurements, would predict 'refractory' patients with high accuracy.

METHODS

Chronic periodontitis patients were treated using scaling and root planing (SRP) followed by maintenance SRP and 3-monthly re-examinations. If there was a loss of mean full mouth attachment or more than three sites appeared with > 2.5 mm new loss within a year, the subjects were re-treated (modified Widman flap surgery and systemically administered tetracycline). If attachment loss as above recurred, the subjects were 'refractory'. Baseline clinical measurements and specific antibody responses were used in a logistic regression model to predict 'refractory' subjects.

RESULTS

Antibody to a peptide portion of lysine decarboxylase (HKL-Ab) and baseline bleeding on probing (BOP) prevalence measurements predicted attachment loss 3 months after initial therapy [pIAL = loss (0) or gain (1)]. IgG antibody contents to a purified antigen from Actinomyces spp. (A-Ab) and streptococcal d-alanyl glycerol lipoteichoic acid (S-Ab) were related in 'refractory' patients (R2 = 0.37, p < 0.01). From the regression equation, the relationship between the antibodies was defined as linear (pLA/S-Ab = 0) or non-linear pLA/S-Ab = 1). Using pLA/S-Ab, pIAL and age, a logistic regression equation was derived from 48 of the patients. Of 59 subjects, 37 had 2-4 mm attachment loss and were assigned as 'refractory' or successfully treated with 86% accuracy.

CONCLUSION

HKL-Ab facilitated an accurate prediction of therapeutic outcome in subjects with moderate periodontitis.

Elevated antibody to D-alanyl lipoteichoic acid indicates caries experience associated with fluoride and gingival health

: BACKGROUND: Acidogenic, acid-tolerant bacteria induce dental caries and require D-alanyl glycerol lipoteichoic acid (D-alanyl LTA) on their cell surface. Because fluoride inhibits acid-mediated enamel demineralization, an elevated antibody response to D-alanyl LTA may indicate subjects with more acidogenic bacteria and, therefore, an association of DMFT with fluoride exposure and gingival health not apparent in low responders. METHODS: Cluster analysis was used to identify low antibody content. Within low and high responders (control and test subjects), the number of teeth that were decayed missing and filled (DMFT), or decayed only (DT) were regressed against fluoride exposure in the water supply and from dentrifice use. The latter was determined from gingival health: prevalences of plaque (PL) and bleeding on probing (BOP), and mean pocket depth (PD). Age was measured as a possible confounding cofactor. RESULTS: In 35 high responders, DMFT associated with length of exposure to fluoridated water (F score), PL and BOP (R2 = 0.51, p < 0.001), whereas in 67 low D-ala-IgG responders, DMFT associated with PL, age, and PD (R2 = 0.26, p < 0.001). BOP correlated strongly with number of 7 7 decayed teeth (DT) in 54 high responders (R2 = 0.57, p < 0.001), but poorly in 97 low responders (R2 = 0.12, p < 0.001). The strength of the PD association with DMFT, or of BOP with DT, in high responders significantly differed from that in low responders (p < 0.05). CONCLUSION: Caries associates with gingival health and fluoridated water exposure in high D-alanyl LTA antibody responders.

Regulation of D-alanyl-lipoteichoic acid biosynthesis in Streptococcus agalactiae involves a novel two-component regulatory system

The dlt operon of gram-positive bacteria comprises four genes (dltA, dltB, dltC, and dltD) that catalyze the incorporation of D-alanine residues into the lipoteichoic acids (LTAs). In this work, we characterized the dlt operon of Streptococcus agalactiae, which, in addition to the dltA to dltD genes, included two regulatory genes, designated dltR and dltS, located upstream of dltA. The dltR gene encodes a 224-amino-acid putative response regulator belonging to the OmpR family of regulatory proteins. The dltS gene codes for a 395-amino-acid putative histidine kinase thought to be involved in the sensing of environmental signals. The dlt operon of S. agalactiae is mainly transcribed from the P(dltR) promoter, which directs synthesis of a 6.5-kb transcript encompassing dltR, dltS, dltA, dltB, dltC, and dltD, and from a weaker promoter, P(dltA), which is located in the 3' extremity of dltS. We demonstrate that P(dltR), but not P(dlA), is activated by DltR in the presence of DltS in D-Ala-deficient LTA mutants resulting from insertional inactivation of the dltA gene, which encodes the cytoplasmic D-alanine-D-alanyl carrier ligase DltA. Expression of the dlt operon does not require DltR and DltS, since the basal activity of P(dltR) is high, being 20-fold that of the constitutive promoter P(aphA-3) which directs synthesis of the kanamycin resistance gene aphA-3 in various gram-positive bacteria. We hypothesize that the role of DltR and DltS in the control of expression of the dlt operon is to maintain the level of D-Ala esters in LTAs at a constant and appropriate value whatever the environmental conditions. The DltA(-) mutant displayed the ability to form clumps in standing culture and exhibited an increased susceptibility to the cationic antimicrobial polypeptide colistin.

Biosynthesis of the glycolipid anchor in lipoteichoic acid of Staphylococcus aureus RN4220: role of YpfP, the diglucosyldiacylglycerol synthase

In Staphylococcus aureus RN4220, lipoteichoic acid (LTA) is anchored in the membrane by a diglucosyldiacylglycerol moiety. The gene (ypfP) which encodes diglucosyldiacylglycerol synthase was recently cloned from Bacillus subtilis and expressed in Escherichia coli (P. Jorasch, F. P. Wolter, U. Zahringer, and E. Heinz, Mol. Microbiol. 29:419-430, 1998). To define the role of ypfP in this strain of S. aureus, a fragment of ypfP truncated from both ends was cloned into the thermosensitive replicon pVE6007 and used to inactivate ypfP. Chloramphenicol-resistant (ypfP::cat) clones did not synthesize the glycolipids monoglucosyldiacylglycerol and diglucosyldiacylglycerol. Thus, YpfP would appear to be the only diglucosyldiacylglycerol synthase in S. aureus providing glycolipid for LTA assembly. In LTA from the mutant, the glycolipid anchor is replaced by diacylglycerol. Although the doubling time of the mutant was identical to that of the wild type in Luria-Bertani (LB) medium, growth of the mutant in LB medium containing 1% glycine was not observed. This inhibition was antagonized by either L- or D-alanine. Moreover, viability of the mutant at 37 degrees C in 0.05 M phosphate (pH 7.2)-saline for 12 h was reduced to <0.1%. Addition of 0.1% D-glucose to the phosphate-saline ensured viability under these conditions. The autolysis of the ypfP::cat mutant in the presence of 0.05% Triton X-100 was 1.8-fold faster than that of the parental strain. Electron microscopy of the mutant revealed not only a small increase in cell size but also the presence of pleomorphic cells. Each of these phenotypes may be correlated with either (or both) a deficiency of free glycolipid in the membrane or the replacement of the usual glycolipid anchor of LTA with diacylglycerol.

Biosynthesis of lipoteichoic acid in Lactobacillus rhamnosus: role of DltD in D-alanylation

The dlt operon (dltA to dltD) of Lactobacillus rhamnosus 7469 encodes four proteins responsible for the esterification of lipoteichoic acid (LTA) by D-alanine. These esters play an important role in controlling the net anionic charge of the poly (GroP) moiety of LTA. dltA and dltC encode the D-alanine-D-alanyl carrier protein ligase (Dcl) and D-alanyl carrier protein (Dcp), respectively. Whereas the functions of DltA and DltC are defined, the functions of DltB and DltD are unknown. To define the role of DltD, the gene was cloned and sequenced and a mutant was constructed by insertional mutagenesis of dltD from Lactobacillus casei 102S. Permeabilized cells of a dltD::erm mutant lacked the ability to incorporate D-alanine into LTA. This defect was complemented by the expression of DltD from pNZ123/dlt. In in vitro assays, DltD bound Dcp for ligation with D-alanine by Dcl in the presence of ATP. In contrast, the homologue of Dcp, the Escherichia coli acyl carrier protein (ACP), involved in fatty acid biosynthesis, was not bound to DltD and thus was not ligated with D-alanine. DltD also catalyzed the hydrolysis of the mischarged D-alanyl-ACP. The hydrophobic N-terminal sequence of DltD was required for anchoring the protein in the membrane. It is hypothesized that this membrane-associated DltD facilitates the binding of Dcp and Dcl for ligation of Dcp with D-alanine and that the resulting D-alanyl-Dcp is translocated to the primary site of D-alanylation.

The dlt operon in the biosynthesis of D-alanyl-lipoteichoic acid in Lactobacillus casei

The D-alanine incorporation system allows Lactobacillus casei to modulate the chemical properties of lipoteichoic acid (LTA) and hence control its proposed functions, i.e., regulation of autolysin action, metal ion binding, and the electromechanical properties of the cell wall. The system requires the D-alanine-D-alanyl carrier protein ligase (Dcl) and the D-alanyl carrier protein (Dcp). Our results indicate that the genes for these proteins are encoded in the dlt operon and that this operon contains at least 2 other genes, dltB and dltD. The aim of this paper is to describe the genetic organization of the operon, the role of the D-alanyl carrier protein, and the function of the putative protein encoded by dltB in the intramembranal translocation of the activated D-alanine.

The absence of D-alanine from lipoteichoic acid and wall teichoic acid alters surface charge, enhances autolysis and increases susceptibility to methicillin in Bacillus subtilis

Summary: In Bacillus subtilis the physiological consequences of depriving lipoteichoic acid and wall teichoic acid of D-alanine ester were analysed using insertional inactivation of the genes of the dlt operon. Mutant strains which lacked positively charged D-alanine ester in teichoic acids bound more positively charged cytochrome C than other strains. These mutant strains also showed enhanced autolysis and a higher susceptibility to methicillin, which was expressed as accelerated wall lysis, a faster loss of viability and a slower recovery in the postantibiotic phase. The effects of methicillin could be suppressed by simultaneous addition of magnesium ions at low concentrations. The degradation of whole bacteria by bone-marrow-derived macrophages was not influenced by the surface charge and alanylation of the teichoic acids had no protective effect.

The D-Alanyl carrier protein in Lactobacillus casei: cloning, sequencing, and expression of dltC

The incorporation of D-alanine into membrane-associated D-alanyl-lipoteichoic acid in Lactobacillus casei requires the 56-kDa D-alanine-D-alanyl carrier protein ligase (Dcl) and the 8.9-kDa D-alanyl carrier protein (Dcp). To identify and isolate the gene encoding Dcp, we have cloned and sequenced a 4.3-kb chromosomal fragment that contains dcl (dltA). In addition to this gene, the fragment contains three other genes, dltB, d1tC, and a partial dltD gene. dltC (246 nucleotides) was subcloned from this region and expressed in Escherichia coli. The product was identified as apo-Dcp lacking the N-terminal methionine (8,787.9 Da). The in vitro conversion of the recombinant apo-Dcp to holo-Dcp by recombinant E. coli holo-ACP synthase provided Dcp which accepts activated D-alanine in the reaction catalyzed by Bcl. The recombinant D-alanyl-Dcp was functionally identical to native D-alanyl-Dcp in the incorporation of D-alanine into lipoteichoic acid. L. casei Dcp is 46% identical to the putative product of dltC in the Bacillus subtilis dlt operon (M. Perego, P. Glaser, A. Minutello, M. A. Strauch, K. Leopold, and W. Fischer, J. Biol. Chem. 270:15598-15606, 1995), and therefore, this gene also encodes Dcp. Comparisons of the primary sequences and predicted secondary structures of the L. casei and B. subtilis Dcps with that of the E. coli acyl carrier protein (ACP) were undertaken together with homology modeling to identify the functional determinants of the donor and acceptor specificities of Dcp. In the region of the phospho-pantetheine attachment site, significant similarity between Dcps and ACPs was observed. This similarity may account for the relaxed acceptor specificity of the Dcps and ACPs in the ligation Of D-alanine catalyzed by Dcl. In contrast, two Dcp consensus sequences, KXXVLDXLA and DXVKXNXD, share little identity with the rest of the ACP family and, thus, may determine the donor specificity of D-alanyl-Dcp in the D-alanylation of membrane-associated D-alanyl-lipoteichoic acid.

Role of the D-alanyl carrier protein in the biosynthesis of D-alanyl-lipoteichoic acid

D-Alanyl-lipoteichoic acid (D-alanyl-LTA) is a widespread macroamphiphile which plays a vital role in the growth and development of gram-positive organisms. The biosynthesis of this polymer requires the enzymic activation of D-alanine for its transfer to the membrane-associated LTA (mLTA). A small, heat-stable, and acidic protein that is required for this transfer was purified to greater than 98% homogeneity from Lactobacillus casei ATCC 7469. This protein, previously named the D-alanine-membrane acceptor ligase (V. M. Reusch, Jr., and F. C. Neuhaus, J. Biol. Chem. 246:6136-6143, 1971), functions as the D-alanyl carrier protein (Dcp). The amino acid composition, beta-alanine content, and N-terminal sequence of this protein are similar to those of the acyl carrier proteins (ACPs) of fatty acid biosynthesis. The isolation of Dcp and its derivative, D-alanyl approximately Dcp, has allowed the characterization of two novel reactions in the pathway for D-alanyl-mLTA biosynthesis: (i) the ligation of Dcp with D-alanine and (ii) the transfer of D-alanine from D-alanyl approximately Dcp to a membrane acceptor. It has not been established whether the membrane acceptor is mLTA or another intermediate in the pathway for D-alanyl-mLTA biosynthesis. Since the D-alanine-activating enzyme (EC 6.1.1.13) catalyzes the ligation reaction, this enzyme functions as the D-alanine-Dcp ligase (Dcl). Dcl also ligated the ACPs from Escherichia coli, Vibrio harveyi, and Saccharopolyspora erythraea with D-alanine. In contrast to the relaxed specificity of Dcl in the ligation reaction, the transfer of D-alanine to the membrane acceptor was highly specific for Dcp and did not occur with other ACPs. This transfer was observed by using only D-[14C]alanyl approximately Dcp and purified L. casei membranes. Thus, D-alanyl approximately Dcp is an essential intermediate in the transfer of D-alanine from Dcl to the membrane acceptor. The formation of D-alanine esters of mLTA provides a mechanism for modulating the net anionic charge in the cell wall.

Biosynthesis of D-alanyl-lipoteichoic acid: cloning, nucleotide sequence, and expression of the Lactobacillus casei gene for the D-alanine-activating enzyme

The D-alanine-activating enzyme (Dae; EC 6.3.2.4) encoded by the dae gene from Lactobacillus casei ATCC 7469 is a cytosolic protein essential for the formation of the D-alanyl esters of membrane-bound lipoteichoic acid. The gene has been cloned, sequenced, and expressed in Escherichia coli, an organism which does not possess Dae activity. The open reading frame is 1,518 nucleotides and codes for a protein of 55.867 kDa, a value in agreement with the 56 kDa obtained by electrophoresis. A putative promoter and ribosome-binding site immediately precede the dae gene. A second open reading frame contiguous with the dae gene has also been partially sequenced. The organization of these genetic elements suggests that more than one enzyme necessary for the biosynthesis of D-alanyl-lipoteichoic acid may be present in this operon. Analysis of the amino acid sequence deduced from the dae gene identified three regions with significant homology to proteins in the following groups of ATP-utilizing enzymes: (i) the acid-thiol ligases, (ii) the activating enzymes for the biosynthesis of enterobactin, and (iii) the synthetases for tyrocidine, gramicidin S, and penicillin. From these comparisons, a common motif (GXXGXPK) has been identified that is conserved in the 19 protein domains analyzed. This motif may represent the phosphate-binding loop of an ATP-binding site for this class of enzymes. A DNA fragment (1,568 nucleotides) containing the dae gene and its putative ribosome-binding site has been subcloned and expressed in E. coli. Approximately 0.5% of the total cell protein is active Dae, whereas 21% is in the form of inclusion bodies. The isolation of this minimal fragment without a native promoter sequence provides the basis for designing a genetic system for modulating the D-alanine ester content of lipoteichoic acid.

Heterogeneity of lipoteichoic acid detected by anion exchange chromatography

A complex polydispersity became apparent when the poly(glycerophosphate) lipoteichoic acid of Enterococcus faecalis was chromatographed on DEAE-Sephadex. The chain length varied between 13 and 33 glycerophosphate residues per lipid anchor. In parallel, the extent of chain glycosylation increased from 0.2 to 0.4 diglucosyl residues per glycerophosphate unit. Substitution with D-alanine ester showed a reverse distribution dropping with increasing chain length from 0.53 to 0.23 mol D-alanine per mol phosphorus. Variations in the fatty acid composition were also observed. The results extent and modify the current picture of lipoteichoic acid biosynthesis. They further suggest that during infection the mammalian organism may be confronted particularly with long-chain less hydrophobic molecular species.

N-acetylmuramoyl-L-alanine amidase assay based on specific radioactive labeling of muropeptide L-alanine: quantitation of the enzyme activity in the autolysin deficient Bacillus subtilis 168, flaD strain

A sensitive and highly reproducible assay for N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28) was devised, based on specific and homogeneous L-[14C]alanine labeling of the substrate, the peptidoglycan. The method involves partial purification of both the enzyme and the substrate and monitoring the muropeptide cleavage by coupling fluorodinitrobenzene to freed L-alanine NH2 groups. After acid hydrolysis of the substrate, the resulting DNP-L-alanine and L-alanine are separated by TLC, and radioactive counts in relevant spots are determined. Application of the method to the autolysin-endowed strain and an autolysis-deficient flaD-bearing mutant has revealed (i) that the N-acetylmuramoyl-L-alanine amidase behaves like an endoenzyme with an apparent Kcat(s-1) of 40, and (ii) that the residual enzyme activity in the flaD bearing strain amounts to 2.5 (+/- 0.1)% of that of the parent strain.

Separation of the poly(glycerophosphate) lipoteichoic acids of Enterococcus faecalis Kiel 27738, Enterococcus hirae ATCC 9790 and Leuconostoc mesenteroides DSM 20343 into molecular species by affinity chromatography on concanavalin A

This study shows for the first time microheterogeneity of 1,3-linked poly(glycerophosphate) lipoteichoic acids. The lipoteichoic acids investigated were those of Enterococcus faecalis Kiel 27738 (I), Enterococcus hirae (Streptococcus faecium) ATCC 9790 (II), and Leuconostoc mesenteroides DMS 20343 (III). Lipoteichoic acids II and III are partially substituted by mono-, di-, tri-, and tetra-alpha-D-glucopyranosyl residues with (1----2) interglycosidic linkages. Lipoteichoic acid I is substituted with alpha-kojibiosyl residues only. Lipoteichoic acids I and III additionally carry D-alanine ester. Lipoteichoic acids were separated on columns of concanavalin-A-Sepharose according to their increasing number of glycosyl substituents per chain. It was evident that all molecular species are usually glycosylated and that alanine ester and glycosyl residues occur on the same chains. The chain lengths of lipoteichoic acid I and II vary between 9-40 glycerophosphate residues, whereas those of lipoteichoic acid III appear to be uniform (33 +/- 2 residues). Molecular species differ in the extent of glycosylation but their content of alanyl residues is fairly constant. All lipoteichoic acids contain a small fraction (5-15%) different in composition from the bulk and most likely reflecting an early stage of biosynthesis. Two procedures for chain length determination of poly(glycerophosphate) lipoteichoic acids are described.

Distribution analyses of chain substituents of lipoteichoic acids by chemical degradation

The lipoteichoic acid from Lactococcus lactis Kiel 48337 was analyzed. It had 61% of its glycerophosphate residues substituted with alpha-D-galactopyranosyl residues. Non-substituted glycerophosphate residues were split off by two alkaline hydrolyses and an intermediate enzymatic phosphomonoester cleavage. The resulting (GalGroP)nGroGal and (GalGroP)nGlc2Gro oligomers were separated by chromatography on DEAE-Sephadex into 10 pairs of molecular species with n from 1 to 10. The relative frequencies of GalGro and these oligomers were close to the values calculated by computer simulation for a random distribution of chain substituents. A similar series of oligomers was obtained in one step by hydrolysis of the lipoteichoic acid with 98% (by vol.) acetic acid. Due to side reactions, the picture was less precise but nevertheless indicative of the same distribution pattern. The data provide indirect evidence that the alanine ester substituents of the native lipoteichoic acid (Ala/P = 0.38) occupy the free positions between the galactosylated oligomers and are therefore themselves distributed randomly.

Nuclear magnetic resonance spectra of lipoteichoic acid

Lipoteichoic acid acids with a range of chemical compositions have been studied using 1H; 13C- and 31P-nuclear magnetic resonance. Proton spectroscopy provided a rapid method for demonstrating whether alanine in a sample is covalently bound to the polyglycerophosphate chains and for monitoring hydrolysis of alanine. The nature of sugar substituents can be determined, with some limitations, from the 13C spectra, and the proportions of glycerol residues substituted by alanine and sugar can be measured. The 31P spectra of lipoteichoic acid provided information about both the degree of substitution and the distribution of the substituent along the polyglycerophosphate chain, except when the substituent was galactose. The polyglycerophosphate chains were shown to undergo rapid internal rotation and no evidence for tertiary structure was found either in the presence or absence of magnesium ions. Magnesium ions exchange rapidly between the bound and free state and the binding constant to lipoteichoic acid of 64 M-1 is typical for monophosphates in aqueous solution. There was no evidence that alanine substitution affects the binding constant for magnesium ions.

'Lipoteichoic acid' of Bifidobacterium bifidum subspecies pennsylvanicum DSM 20239. A lipoglycan with monoglycerophosphate side chains

The lipid macroamphiphile of Bifidobacterium bifidum subsp. pennsylvanicum DSM 20239 was extracted with phenol/water and purified by treatment with nucleases and hydrophobic interaction chromatography. From analytical data, the results of Smith degradation, hydrolysis with HF and methylation studies, the following structure is proposed: (formula; see text) where n and m are approximately 7-10 and 8-15, respectively. The monoglycerophosphate residues have the sn-glycero-1-phosphate configuration; 20-50% of them are substituted with L-alanine in ester linkage. The lipid anchor is most likely a galactosyldiacylglycerol, part of which carries a third fatty acid. This is the first example among gram-positive bacteria of a glycerophosphate-containing lipid macroamphiphile that carries the glycerophosphate residues as monomeric side chains on a lipoglycan. Further, it contains L-alanine in place of the D-alanine found in lipoteichoic acids.

Assembly of D-alanyl-lipoteichoic acid in Lactobacillus casei: mutants deficient in the D-alanyl ester content of this amphiphile

D-Alanyl-lipoteichoic acid (D-alanyl-LTA) from Lactobacillus casei ATCC 7469 contains a poly(glycerophosphate) moiety that is acylated with D-alanyl ester residues. The physiological function of these residues is not well understood. Five mutant strains of this organism that are deficient in the esters of this amphiphile were isolated and characterized. When compared with the parent, strains AN-1 and AN-4 incorporated less than 10% of D-[14C]alanine into LTA, whereas AN-2, AN-3, and AN-5 incorporated 50%. The synthesis of D-[14C]alanyl-lipophilic LTA was virtually absent in the first group and was approximately 30% in the second group. The mutant strains synthesized and selected the glycolipid anchor for LTA assembly. In addition, all of the strains synthesized the poly(glycerophosphate) moiety of LTA to the same extent as did the parent or to a greater extent. It was concluded that the membranes from the mutant strains AN-1 and AN-4 are defective for D-alanylation of LTA even though acceptor LTA is present. Mutant strains AN-2 and AN-3 appear to be partially deficient in the amount of the D-alanine-activating enzyme. Aberrant morphology and defective cell separation appear to result from this deficiency in D-alanyl ester content.

Maintenance of D-alanine ester substitution of lipoteichoic acid by reesterification in Staphylococcus aureus

Toluene-treated Staphylococcus aureus cells did not synthesize teichoic acid and lipoteichoic acid under the conditions used. The organism displayed, however, a high capacity of incorporating D-[14C]alanine into previously formed polymers. The reaction was dependent on ATP and enhanced by magnesium ions. The incorporation rate into lipoteichoic acid correlated with the rate of loss of alanine ester which occurred through transfer to teichoic acid and base-catalyzed hydrolysis. At pH 6.5 the loss (20% within 4 h) was completely compensated for by reesterification. At pH 7.5 the loss was 60%, but by accelerated incorporation it was reduced to 10%. Incorporation was also enhanced when the original substitution of lipoteichoic acid was lowered by previous growth of S. aureus at high salt concentration. The newly added alanine was randomly distributed along the poly(glycerophosphate) chain. The decreased alanine substitution of lipoteichoic acid after growth at high salt concentration was shown to result from a direct inhibition of alanine incorporation.

Biosynthesis of D-alanyl-lipoteichoic acid by Lactobacillus casei: interchain transacylation of D-alanyl ester residues

Lipoteichoic acid (LTA) from Lactobacillus casei contains poly(glycerophosphate) substituted with D-alanyl ester residues. The distribution of these residues in the in vitro-synthesized polymer is uniform. Esterification of LTA with D-alanine may occur in one of two modes: (i) addition at random or (ii) addition at a defined locus in the poly(glycerophosphate) chain followed by redistribution of the ester residues. A time-dependent transacylation of these residues from D-[14C]alanyl-lipophilic LTA to hydrophilic acceptor was observed. The hydrophilic acceptor was characterized as D-alanyl-hydrophilic LTA. This transacylation requires neither ATP nor the D-alanine incorporation system, i.e., the D-alanine activating enzyme and D-alanine:membrane acceptor ligase. No evidence for an enzyme-catalyzed transacylation reaction was observed. We propose that this process of transacylation may be responsible for the redistribution of D-alanyl residues after esterification to the poly(glycerophosphate). As a result, it is difficult to distinguish between these proposed modes of addition.

D-Alanyl-substituted glycerol lipoteichoic acid in culture fluids of Streptococcus mutans strains GS-5 and BHT

The content and D-alanyl ester complement of lipoteichoic acid from stationary-phase culture filtrates of Streptococcus mutans (strains BHT and GS-5; serotypes b and c) were determined chemically and serologically. A third less lipoteichoic acid was obtained from strain GS-5 than from strain BHT. This lipoteichoic acid had an increased mobility on immunoelectrophoresis after exposure overnight at pH 8 and a 10-fold greater content of alanine per mole of glycerol.

Lipopolymers, isoprenoids, and the assembly of the gram-positive cell wall

Several lines of evidence suggest that Gram-positive bacterial cell surface polymers are synthesized by stepwise addition of polymer subunits to an amphipathic acceptor. In the case of membrane-bound lipopolymers such as mannan and lipoteichoic acid, the finished product may be covalently linked to a lipid anchor. In the case of polymers that are transferred into preexisting cell wall, such as teichoic acid and peptidoglycan, two alternative fates might be possible: (1) transfer into wall with concomitant or later cleavage of the lipid anchor, with recycling of the lipid anchor or secretion of the lipid anchor into the growth medium, and (2) transfer into wall without cleavage of the lipid anchor, resulting in maintenance of the covalent relationship between lipid anchor and polymer chain. In the latter case, a close relationship should be established between the cell wall and the plasma membrane. A number of Gram-positive bacteria have been shown to be resistant to plasmolysis. Therefore, a model for the assembly of the Gram-positive cell wall is proposed which takes into account a role for lipopolymeric intermediates and which views the establishment of resistance to plasmolysis as the natural consequence of such a mechanism.

Biosynthesis of D-alanyl-lipoteichoic acid: role of diglyceride kinase in the synthesis of phosphatidylglycerol for chain elongation

Lipophilic and hydrophilic D-alanyl-lipoteichoic acids are elongated in Lactobacillus casei by the transfer of sn-glycerol 1-phosphate units from phosphatidylglycerol to the poly(glycerophosphate) moiety of the polymer. These sn-glycerol 1-phosphate units are added to the end of the poly(glycerophosphate) which is distal to the glycolipid anchor; 1,2-diglyceride results from this addition. The presence of a diglyceride kinase was suggested by the ATP-dependent phosphorylation of 1,2-diglyceride to phosphatidic acid. Inorganic phosphate was used to initiate the synthesis of lipophilic lipoteichoic acid (LTA) and the elongation of both lipophilic and hydrophilic LTA. Three observations suggest that phosphate and other anions play a role in the in vitro synthesis of LTA and its precursors. First, the conversion of 1,2-diglyceride to phosphatidic acid by diglyceride kinase was stimulated. Second, the synthesis of phosphatidylglycerol was increased. Third, the elongation of lipophilic and hydrophilic LTA was enhanced. These observations indicated that one effect of phosphate might be to enhance the utilization of 1,2-diglyceride for the synthesis of phosphatidic acid. This phospholipid is a precursor of phosphatidylglycerol, the donor of sn-glycerol 1-phosphate for elongation of LTA.

Biosynthesis of glucosyl monophosphoryl undecaprenol and its role in lipoteichoic acid biosynthesis

A glucophospholipid was detected in an incubation mixture containing UDP-glucose, MgCl2, ATP, and a particulate enzyme prepared from Streptococcus sanguis. The synthesis of this lipid was inhibited strongly by UDP and moderately by UMP. The molar ratio of glucose to phosphate in the purified lipid was found to be 1:1. Glucose and glucose 1-phosphate were released by mild alkaline hydrolysis of the glucophospholipid. The lipid produced by mild acid degradation of the purified lipid yielded a thin-layer chromatographic profile similar to that of acid-treated undecaprenol. One of the minor components exhibited the same mobility as untreated undecaprenol. To characterize further the lipid moiety of the glucophospholipid, a polyisoprenol was purified from the neutral lipid of S. sanguis. The polyisoprenol was converted in the presence of ATP, UDP-glucose, and the particulate enzyme into a lipid which exhibited the same thin-layer chromatographic mobility as the glucophospholipid. The structure of the polyisoprenol was determined by nuclear magnetic resonance and mass spectrometry to be an undecaprenol with an internal cis-trans ratio of 7:2. These results indicate that the glucophospholipid is glucosyl monophosphoryl undecaprenol. The glucosyl moiety of the glucophospholipid was shown to be incorporated in the presence of the particulate enzyme into a macromolecule which was characterized as a lipoteichoic acid by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and DEAE-cellulose column chromatography. This result indicates that glucosyl monophosphoryl undecaprenol is the direct glucosyl donor in the synthesis of lipoteichoic acid.

Teichoic and teichuronic acids: biosynthesis, assembly, and location

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Effect of alanine ester substitution and other structural features of lipoteichoic acids on their inhibitory activity against autolysins of Staphylococcus aureus

Native substitution with the D-alanine ester of lipoteichoic acids (LTAs) affects their immunological properties, the capacity to bind divalent cations, and LTA carrier activity. In this study we tested the influence of the D-alanine ester on anti-autolytic activity, using extracellular autolysin from Staphylococcus aureus and nine LTAs with alanine/phosphorus molar ratios of between 0.23 and 0.71. The inhibitory activity, highest with alanine-free LTA, exponentially decreased with increasing alanine content, approaching zero at substitutions of greater than 0.6. Correspondingly, dipolar ionic phospholipids were not inhibitory, in contrast to negatively charged ones. Glycosylation of LTA up to an extent of 0.5 did not depress inhibitory activity, and even at a degree of 0.8 the effect was comparatively small. On comparison of LTAs from various sources, differences in lipid structures and chain lengths were without effect. The inhibitory activity drastically decreased when the glycolipid carried a single glycerophosphate residue or the hydrophilic chain had the unusual structure [6 leads to Gal(alpha 1--6)Gal(alpha 1--3)Gro-(2 comes from 1 alpha Gal)-P]n, in which digalactosyl moieties connect the alpha-galactosylated glycerophosphate units. Principally, the same results were obtained with the more complex system of autolysis of S. aureus cells. We hypothesize that the anti-autolytic activity of LTA resides in a sequence of glycerophosphate units and that the negative charges of appropriately spaced phosphodiester groups play a crucial role. The alanine ester effect is discussed with respect to the putative in vivo regulation of autolysins by LTA.

Biosynthesis of D-alanyl-lipoteichoic acid in Lactobacillus casei: D-alanyl-lipophilic compounds as intermediates

D-Alanyl-lipoteichoic acid (D-alanyl-LTA) from Lactobacillus casei contains a poly(glycerol phosphate) moiety that is selectively acylated with D-alanine ester residues. To characterize further the mechanism of D-alanine substitution, intermediates were sought that participate in the assembly of this LTA. From the incorporation system utilizing either toluene-treated cells or a combination of membrane fragments and supernatant fraction, a series of membrane-associated D-[14C]alanyl-lipophilic compounds was found. The assay of these compounds depended on their extractability into monophasic chloroform-methanol-water (0.8:3.2:1.0, vol/vol/vol) and subsequent partitioning into chloroform. Four lines of evidence suggested that the D-alanyl-lipophilic compounds are intermediates in the synthesis of D-alanyl-LTA. First, partial degradation of the poly(glycerol phosphate) moiety of D-alanyl-LTA by phosphodiesterase II/phosphatase from Aspergillus niger generated a series of D-alanyl-lipophilic compounds similar to those extracted from the toluene-treated cells during the incorporation of D-alanine. Second, enzymatic degradation of the D-alanyl-lipophilic compounds by the above procedure gave D-alanyl-glycerol, the same degradation product obtained from D-alanyl-LTA. Third, the incorporation of D-alanine into these compounds required the same components as the incorporation of D-alanine into membrane-associated D-alanyl-LTA. Fourth, the phosphate-induced loss of D-[14C]alanine-labeled lipophilic compounds could be correlated with the stimulation of phosphatidylglycerol synthesis in the presence of excess phosphate. We interpreted these experiments to indicate that the D-alanyl-lipophilic compounds are D-alanyl-LTA with short polymer chains and are most likely intermediates in the assembly of the completed polymer, D-alanyl-LTA.

Attachment of the main chain to the linkage unit in biosynthesis of teichoic acids

The main chain of teichoic acids can be assembled in cell-free membrane preparations by the transfer of residues from the appropriate nucleotide precursors to an incompletely characterized amphiphilic molecule, lipoteichoic acid carrier (LTC). However, in the cell wall, the main chain is attached to peptidoglycan through a linkage unit which is synthesized independently. It is believed that, in these cell-free systems, lipid intermediates carrying linkage units are also able to accept residues directly from nucleotide precursors to build up the main chain. In this paper, we have shown that the main chain attached to LTC was transferred from LTC to lipids containing the linkage unit. Thus, in these systems, there appear to be two routes to the biosynthesis of teichoic acid-linkage unit complexes, one by direct assembly of the main chain on linkage unit lipids and the other by transfer of the preassembled main chain from LTC to the linkage unit. It was also shown that linkage unit lipids from different organisms were interchangeable and that these were used for polymer synthesis by Bacillus subtilis 3610, in which the teichoic acid is a poly(glycerol phosphate).