SEPARATION OF TEICHOIC ACID OF STAPHYLOCOCCUS AUREUS INTO TWO IMMUNOLOGICALLY DISTINCT SPECIFIC POLYSACCHARIDES WITH ALPHA- AND BETA-N-ACETYLGLUCOSAMINYL LINKAGES RESPECTIVELY. ANTIGENICITY OF THEICHOIC ACIDS IN MAN

Structural investigation of human S. aureus-targeting antibodies that bind wall teichoic acid

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a growing health threat worldwide. Efforts to identify novel antibodies that target S. aureus cell surface antigens are a promising direction in the development of antibiotics that can halt MRSA infection. We biochemically and structurally characterized three patient-derived MRSA-targeting antibodies that bind to wall teichoic acid (WTA), which is a polyanionic surface glycopolymer. In S. aureus, WTA exists in both α- and β-forms, based on the stereochemistry of attachment of a N-acetylglucosamine residue to the repeating phosphoribitol sugar unit. We identified a panel of antibodies cloned from human patients that specifically recognize the α or β form of WTA, and can bind with high affinity to pathogenic wild-type strains of S. aureus bacteria. To investigate how the β-WTA specific antibodies interact with their target epitope, we determined the X-ray crystal structures of the three β-WTA specific antibodies, 4462, 4497, and 6078 (Protein Data Bank IDs 6DWI, 6DWA, and 6DW2, respectively), bound to a synthetic WTA epitope. These structures reveal that all three of these antibodies, while utilizing distinct antibody complementarity-determining region sequences and conformations to interact with β-WTA, fulfill two recognition principles: binding to the β-GlcNAc pyranose core and triangulation of WTA phosphate residues with polar contacts. These studies reveal the molecular basis for targeting a unique S. aureus cell surface epitope and highlight the power of human patient-based antibody discovery techniques for finding novel pathogen-targeting therapeutics.

Structure and Mechanism of Staphylococcus aureus TarS, the Wall Teichoic Acid β-glycosyltransferase Involved in Methicillin Resistance

In recent years, there has been a growing interest in teichoic acids as targets for antibiotic drug design against major clinical pathogens such as Staphylococcus aureus, reflecting the disquieting increase in antibiotic resistance and the historical success of bacterial cell wall components as drug targets. It is now becoming clear that β-O-GlcNAcylation of S. aureus wall teichoic acids plays a major role in both pathogenicity and antibiotic resistance. Here we present the first structure of S. aureus TarS, the enzyme responsible for polyribitol phosphate β-O-GlcNAcylation. Using a divide and conquer strategy, we obtained crystal structures of various TarS constructs, mapping high resolution overlapping N-terminal and C-terminal structures onto a lower resolution full-length structure that resulted in a high resolution view of the entire enzyme. Using the N-terminal structure that encapsulates the catalytic domain, we furthermore captured several snapshots of TarS, including the native structure, the UDP-GlcNAc donor complex, and the UDP product complex. These structures along with structure-guided mutants allowed us to elucidate various catalytic features and identify key active site residues and catalytic loop rearrangements that provide a valuable platform for anti-MRSA drug design. We furthermore observed for the first time the presence of a trimerization domain composed of stacked carbohydrate binding modules, commonly observed in starch active enzymes, but adapted here for a poly sugar-phosphate glycosyltransferase.

Historically, β-lactam class antibiotics such as methicillin have been very successful in the treatment of bacterial infections, effectively destroying bacteria by rupturing their cell walls while posing little harm to the human organism. In recent years, however, the alarming emergence of Methicillin Resistant S. aureus or MRSA has resulted in a world-wide health crisis, calling on new strategies to combat pathogenesis and antibiotic resistance. As such, understanding the pathways and players that orchestrate resistance is important for overcoming these mechanisms and restoring our powerful β-lactam antibiotic arsenal. In this article we describe the crystal structure of TarS, an enzyme responsible for the glycosylation of wall teichoic acid polymers of the S. aureus cell wall, a process that has been shown to be specifically responsible for methicillin resistance in MRSA. TarS is therefore a promising drug target whose inhibition in combinational therapies would result in MRSA re-sensitization to β-lactam antibiotics. Here we present the first structure of TarS together with several snap-shots of its substrate/product complexes, and elucidate important catalytic features that are valuable for rational drug design efforts to combat resistance in MRSA.

The staphylococcal surface-glycopolymer wall teichoic acid (WTA) is crucial for complement activation and immunological defense against Staphylococcus aureus infection

Staphylococcus aureus is a Gram-positive bacterial pathogen that is decorated by glycopolymers, including wall teichoic acid (WTA), peptidoglycan, lipoteichoic acid, and capsular polysaccharides. These bacterial surface glycopolymers are recognized by serum antibodies and a variety of pattern recognition molecules, including mannose-binding lectin (MBL). Recently, we demonstrated that human serum MBL senses staphylococcal WTA. Whereas MBL in infants who have not yet fully developed adaptive immunity binds to S. aureus WTA and activates complement serum, MBL in adults who have fully developed adaptive immunity cannot bind to WTA because of an inhibitory effect of serum anti-WTA IgG. Furthermore, we showed that human anti-WTA IgGs purified from pooled adult serum IgGs triggered activation of classical complement-dependent opsonophagocytosis against S. aureus. Because the epitopes of WTA that are recognized by anti-WTA IgG and MBL have not been determined, we constructed several S. aureus mutants with altered WTA glycosylation. Our intensive biochemical studies provide evidence that the β-GlcNAc residues of WTA are required for the induction of anti-WTA IgG-mediated opsonophagocytosis and that both β- and α-GlcNAc residues are required for MBL-mediated complement activation. The molecular interactions of other S. aureus cell wall components and host recognition proteins are also discussed. In summary, in this review, we discuss the biological importance of S. aureus cell surface glycopolymers in complement activation and host defense responses.

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.

Structure and mechanism of Staphylococcus aureus TarM, the wall teichoic acid α-glycosyltransferase

Unique to Gram-positive bacteria, wall teichoic acids are anionic glycopolymers cross-stitched to a thick layer of peptidoglycan. The polyol phosphate subunits of these glycopolymers are decorated with GlcNAc sugars that are involved in phage binding, genetic exchange, host antibody response, resistance, and virulence. The search for the enzymes responsible for GlcNAcylation in Staphylococcus aureus has recently identified TarM and TarS with respective α- and β-(1-4) glycosyltransferase activities. The stereochemistry of the GlcNAc attachment is important in balancing biological processes, such that the interplay of TarM and TarS is likely important for bacterial pathogenicity and survival. Here we present the crystal structure of TarM in an unusual ternary-like complex consisting of a polymeric acceptor substrate analog, UDP from a hydrolyzed donor, and an α-glyceryl-GlcNAc product formed in situ. These structures support an internal nucleophilic substitution-like mechanism, lend new mechanistic insight into the glycosylation of glycopolymers, and reveal a trimerization domain with a likely role in acceptor substrate scaffolding.

How Listeria monocytogenes organizes its surface for virulence

Listeria monocytogenes is a Gram-positive pathogen responsible for the manifestation of human listeriosis, an opportunistic foodborne disease with an associated high mortality rate. The key to the pathogenesis of listeriosis is the capacity of this bacterium to trigger its internalization by non-phagocytic cells and to survive and even replicate within phagocytes. The arsenal of virulence proteins deployed by L. monocytogenes to successfully promote the invasion and infection of host cells has been progressively unveiled over the past decades. A large majority of them is located at the cell envelope, which provides an interface for the establishment of close interactions between these bacterial factors and their host targets. Along the multistep pathways carrying these virulence proteins from the inner side of the cytoplasmic membrane to their cell envelope destination, a multiplicity of auxiliary proteins must act on the immature polypeptides to ensure that they not only maturate into fully functional effectors but also are placed or guided to their correct position in the bacterial surface. As the major scaffold for surface proteins, the cell wall and its metabolism are critical elements in listerial virulence. Conversely, the crucial physical support and protection provided by this structure make it an ideal target for the host immune system. Therefore, mechanisms involving fine modifications of cell envelope components are activated by L. monocytogenes to render it less recognizable by the innate immunity sensors or more resistant to the activity of antimicrobial effectors. This review provides a state-of-the-art compilation of the mechanisms used by L. monocytogenes to organize its surface for virulence, with special focus on those proteins that work “behind the frontline”, either supporting virulence effectors or ensuring the survival of the bacterium within its host.

Glycoepitopes of staphylococcal wall teichoic acid govern complement-mediated opsonophagocytosis via human serum antibody and mannose-binding lectin

Serum antibodies and mannose-binding lectin (MBL) are important host defense factors for host adaptive and innate immunity, respectively. Antibodies and MBL also initiate the classical and lectin complement pathways, respectively, leading to opsonophagocytosis. We have shown previously that Staphylococcus aureus wall teichoic acid (WTA), a cell wall glycopolymer consisting of ribitol phosphate substituted with α- or β-O-N-acetyl-d-glucosamine (GlcNAc) and d-alanine, is recognized by MBL and serum anti-WTA IgG. However, the exact antigenic determinants to which anti-WTA antibodies or MBL bind have not been determined. To answer this question, several S. aureus mutants, such as α-GlcNAc glycosyltransferase-deficient S. aureus ΔtarM, β-GlcNAc glycosyltransferase-deficient ΔtarS, and ΔtarMS double mutant cells, were prepared from a laboratory and a community-associated methicillin-resistant S. aureus strain. Here, we describe the unexpected finding that β-GlcNAc WTA-deficient ΔtarS mutant cells (which have intact α-GlcNAc) escape from anti-WTA antibody-mediated opsonophagocytosis, whereas α-GlcNAc WTA-deficient ΔtarM mutant cells (which have intact β-GlcNAc) are efficiently engulfed by human leukocytes via anti-WTA IgG. Likewise, MBL binding in S. aureus cells was lost in the ΔtarMS double mutant but not in either single mutant. When we determined the serum concentrations of the anti-α- or anti-β-GlcNAc-specific WTA IgGs, anti-β-GlcNAc WTA-IgG was dominant in pooled human IgG fractions and in the intact sera of healthy adults and infants. These data demonstrate the importance of the WTA sugar conformation for human innate and adaptive immunity against S. aureus infection.

Wall teichoic acids of gram-positive bacteria

The peptidoglycan layers of many gram-positive bacteria are densely functionalized with anionic glycopolymers known as wall teichoic acids (WTAs). These polymers play crucial roles in cell shape determination, regulation of cell division, and other fundamental aspects of gram-positive bacterial physiology. Additionally, WTAs are important in pathogenesis and play key roles in antibiotic resistance. We provide an overview of WTA structure and biosynthesis, review recent studies on the biological roles of these polymers, and highlight remaining questions. We also discuss prospects for exploiting WTA biosynthesis as a target for new therapies to overcome resistant infections.

Preparation of Cell Wall Antigens of Staphylococcus aureus

Cell walls were prepared from Staphylococcus aureus strains Copenhagen and 263 by high-speed mixing in the presence of glass beads followed by differential centrifugation. Insoluble peptidoglycan complexes were derived from cell walls by extraction of teichoic acid with 10% trichloroacetic acid. Intact teichoic acid was prepared from each strain by digestion of cell walls with lysostaphin and isolated by column chromatography. Soluble glycopeptide (peptidoglycan in which only the glycan has been fragmented) and the stable complex of teichoic acid with glycopeptide were prepared by digestion of cell walls with Chalaropsis B endo-N-acetylmuramidase and were separated by column chromatography. Amino acid and amino sugar contents of walls and subunits of walls were comparable to those reported by others.

Glycosylation of wall teichoic acid in Staphylococcus aureus by TarM

Wall teichoic acid (WTA) glycopolymers are major constituents of cell envelopes in Staphylococcus aureus and related gram-positive bacteria with important roles in cell wall maintenance, susceptibility to antimicrobial molecules, biofilm formation, and host interaction. Most S. aureus strains express polyribitol phosphate WTA substituted with D-alanine and N-acetylglucosamine (GlcNAc). WTA sugar modifications are highly variable and have been implicated in bacteriophage susceptibility and immunogenicity, but the pathway and enzymes of staphylococcal WTA glycosylation have remained unknown. Revisiting the structure of S. aureus RN4220 WTA by NMR analysis revealed the presence of canonical polyribitol phosphate WTA bearing only alpha-linked GlcNAc substituents. A RN4220 transposon mutant resistant to WTA-dependent phages was identified and shown to produce altered WTA, which exhibited faster electrophoretic migration and lacked completely the WTA alpha-GlcNAc residues. Disruption of a gene of unknown function, renamed tarM, was responsible for this phenotype. Recombinant TarM was capable of glycosylating WTA in vitro in a UDP-GlcNAc-dependent manner, thereby confirming its WTA GlcNAc-transferase activity. Deletion of the last seven amino acids from the C terminus abolished the activity of TarM. tarM-related genes were found in the genomes of several WTA-producing bacteria, suggesting that TarM-mediated WTA glycosylation is a general pathway in gram-positive bacteria. Our study represents a basis for dissecting the biosynthesis and function of glycosylated WTA in S. aureus and other bacteria.

THE INTERRELATIONSHIP BETWEEN MUCOPEPTIDE AND RIBITOL TEICHOIC ACID FORMATION AS SHOWN BY THE EFFECT OF INHIBITORS

1. The biosynthesis of teichoic acid in cell suspensions of two strains of Staphylococcus aureus is partially inhibited by the same low concentrations of penicillin that inhibit mucopeptide synthesis by 90-100%. Further increase in the concentration of the antibiotic by several hundred-fold still fails to cause any greater inhibition of teichoic acid synthesis. 2. Other conditions, such as amino acid deficiency or the presence of cycloserine or 5-fluorouracil, that inhibit mucopeptide synthesis also inhibit teichoic acid formation. 3. The degree of inhibition of teichoic acid synthesis caused by relatively high concentrations (10mug./ml.) of benzylpenicillin depends critically on the age of the culture from which the cell suspensions have been prepared. 4. No significant amounts of soluble teichoic acid have been found in the fluid from cells incubated in the presence of penicillin. 5. A high proportion of the teichoic acid formed in the presence of penicillin can be removed from wall preparations at room temperature by 0.1n-ammonia. This is not true of the teichoic acid formed in the absence of penicillin. 6. The teichoic acid extracted with ammonia from preparations of cell walls made from cells treated with penicillin is excluded from Sephadex G-25, has a low molar ratio of glucosamine to phosphorus and contains muramic acid, alanine, glutamic acid, glycine and lysine. 7. The implications of these results for the mechanism of action of penicillin are discussed.

STUDIES ON HUMAN ANTIBODIES. 3. AMINO ACID COMPOSITION OF FOUR ANTIBODIES FROM ONE INDIVIDUAL

Antilevan, antidextran, antiteichoic acid, anti-"A" and normal γG, all isolated from a single human, as well as pooled γG and γM, were analyzed for amino acid content. Differences ranging from 7 to 32 residues were found among these antibodies in glycine, valine, leucine, tyrosine, arginine, lysine, and threonine content. These conspicuous differences in amino acid composition were not correlated with the Gm type of these antibodies. Hydroxylysine was found in two of the four antibodies, antidextran and antiteichoic acid, and in γM- immunoglobulin. No hydroxylysine was found in γG- globulins. These findings probably account for discrepancies in the literature concerning the occurrence of this residue in antibody protein.

Study of Staphylococcus aureus teichoic acid immunodominant site by help of synthetic haptens

The beta ribitol teichoic acid was extracted and purified from Staphylococcus aureus strain Wood 46 and chemically and immunologically characterised. Rabbit antiserum was prepared against formalin killed Staphylococcus aureus cells. Liquid phase immunoprecipitation of the beta ribitol teichoic acid-anti-Staphylococcus aureus serum system was studied by laser nephelometry. Various mono- and disaccharides (N-acetyl-glucosamine-ribitol with alpha- or beta-linkage and N-acetyl-glucosamine-ribitol-phosphate with beta-linkage) were prepared by organic synthesis, reproducing part of the ribitol teichoic acid molecule. Inhibition by those mono- or disaccharides of the precipitation of the beta-ribitol teichoic acid-Staphylococcus aureus antibodies system was studied quantitatively by determining inhibitory ratio of each inhibitor. Glucose, ribitol and glucosamine were weak inhibitors whereas N-acetyl-glucosamine was a better one, stronger than disaccharide with an alpha-linkage. The beta linked disaccharide and beta-methyl-N-acetyl-glucosamine gave comparable inhibition and both compounds were effective inhibitors. The most potent inhibitor was phosphorylated beta-linked disaccharide which inhibited 25% more than the same disaccharide without phosphorus. Thus, the function of phosphorus in Staphylococcus aureus beta ribitol teichoic acid recognition by antibodies was demonstrated.

Isolation of Staphylococcus aureus clumping factor

Immunochemically identical components were isolated from water-soluble phases of five Staphylococcus aureus strains by affinity chromatography on fibrinogen-linked Sepharose 4B. The elution was performed with 1 M MgCl2. The component could be isolated from sonicated preparations of whole cells, cell walls, and extracellular products of S. aureus but not from sonicated preparations of staphylococcal L-forms or from Staphylococcus epidermidis. Investigations of the eluted component by immunoelectrophoresis and Western blot analysis by use of different polyspecific antibodies to S. aureus raised in rabbits revealed only one immunoprecipitate or one band. By means of gel filtration on Sepharose CL 6B and sodium dodecyl sulfate-polyacrylamide gel electrophoresis a molecular mass of 420,000 and 360,000 was found, respectively. Chemical analysis showed a carbohydrate content of about 20% by weight. By crossed immunoelectrophoresis the isolated component was demonstrated to bind to human fibrinogen. The finding that this purified component inhibited the fibrinogen-induced clumping of staphylococci strongly suggests that the component is the S. aureus clumping factor.

Kinetics of phagocytosis of Staphylococcus aureus by alveolar and peritoneal macrophages

The rate of uptake of radiolabeled Staphylococcus aureus by macrophages in vitro was studied by use of Lineweaver-Burk analysis. It was found that competition for ingestion by excess unlabeled particles, either staphylococci or unrelated particles, resulted in diminished uptake of the labeled particles and that opsonization of particles with specific antiserum enhanced that uptake solely by altering the maximum velocity of uptake (Vmax). Uptake of radiolabeled staphylococci opsonized with specific antiserum was not inhibited by excess numbers of unopsonized organisms; the ingestion was inhibited by excess numbers of opsonized unlabeled organisms, and that inhibition was characterized by depression of Vmax. Inhibition of phagocytosis by indoacetate and cytochalasin B resulted from depression in both Vmax and Michaelis constate (Km). In addition, the phagocytic function of macrophages improved during in vitro culture, a phenomenon which was particularly striking for alveolar macrophages. That enhancement of activity resulted from improvements in both Vmax and Km. Addition of opsonizing antibody at any stage of in vitro maturation resulted in further increases in phagocytic uptake, increases which affected only Vmax. The in vitro maturation of phagocytic function by alveolar macrophages could be inhibited by both 2-deoxy-D-glucose and cycloheximide, but not by culture in hypoxia. The data indicate that the terms of Lineweaver-Burk analysis cna be correlated with functional aspects of phagocytosis and that Vmax represents the avidity of the macrophage surface for the particle, whereas Km is an index of the capacity of the cell for ingestion.

Correlation of antistaphylococcal antibody titers with severity of staphylococcal disease

Counterimmunoelectrophoresis (CIE) was utilized to determine antistaphylococcal precipitin antibody titers in patients with various staphylococcal diseases and in control subjects. Patients with staphylococcal disease comprised five cases of endocarditis, 22 of deep tissue infection (including seven cases of osteomyelitis), six of bacteremia and six of skin infection. Control subjects consisted of 31 patients with nonstaphylococcal bacteremias, 29 hospitalized patients without infection and 30 healthy subjects. Antistaphylococcal antibodies were present in all patients with staphylococcal endocarditis and deep tissue staphylococcal infection, and all but three had titers greater than or equal to 1:4. No significant difference in titers was found between these two groups of patients. Antibodies, although present in some patients in the other categories, were detected less frequently; only two patients had titers greater than or equal to 1:4. Thus, an antistaphylococcal antibody titer by CIE of 1:4 or greater may be an additional diagnostic parameter helpful in distinguishing patients with staphylococcal endocarditis or deep tissue infection from those with other forms of staphylococcal infection and from noninfected subjects.

Teichoic acids in pathogenic Staphylococcus aureus

Twenty-six strains of Staphylococcus aureus obtained from patients with endocarditis were studied for the production of alpha- and/or beta-ribitol teichoic acid (TA), using highly specific anti-TA antibodies prepared in rabbits. A counterimmunoelectrophoretic assay was used. Beta-TA was the predominant residue produced by all strains; alpha-TA was found in all strains, but in smaller amounts and with much strain-to-strain variations. Antibodies in patients' sera were found against beta-TA in higher titers and for longer periods than were anti-alpha-TA antibodies. Antibodies against one or both TA residues were present in all but one of 26 patients.

Relationship of capsular type to biochemical and immunological properties of teichoic acid preparations from unencapsulated strains of Staphylococcus aureus

We investigated the biochemical and immunological characteristics of teichoic acid preparations (TAP) obtained from four unencapsulated strains of Staphylococcus aureus which nonetheless, according to the serum-soft agar technique, produced capsular type antigen and were representative of the four types A, B, C, and D. In the agar diffusion test, TAP of each strain produced a single precipitin line only against rabbit antisera corresponding to the homologous capsular type; no lines were observed against antisera to the heterologous capsular type. All TAP were ribitol type except one, glycerol, prepared from a capsular type D strain. Major acetylglucosaminyl residues of TAP from strains having capsular type A and C antigens were attached to the polyribitol phosphate by beta-linkage, whereas TAP from a type B antigen strain had an alpha-linkage; type D antigen was attached to the polyglycerol phosphate by the beta-linkage. Chemical analyses and infrared spectrograms of these TAP further confirmed their heterogeneous nature.

Bacillus pumilus polysaccharide cross-reactive with meningococcal group A polysaccharide

A polysaccharide, antigenically and structurally related to meningococcal group A polysaccharide, was isolated from Bacillus pumilus Sh-17. This enteric bacterium has been implicated as a source of natural meningococcal group A immunity (Myerowitz et al., 1973). The B. pumilus polysaccharide was composed of a homopolymer of (1-6)-N-acetyl-manosamine-1-phosphate, glycerol phosphate teichoic acid-containing N-acetylglucosamine and alkali-labile alanine esters, and a mucopeptide. The cross-reaction was due to the poly-(1-6)-N-acetyl-mannosamine-1-phosphate in the B. pumilus and the meningococcal group A polysaccharides, based on the following evidence. Both polysaccharides contained N-acetyl-mannosamine phosphate. Periodate oxidized the mannosamine phosphate residues of the polysaccharide and destroyed their precipitating activity with meningococcal group A antiserum. Mild acid treatment released phosphomonoesters and destroyed the meningococcal group A precipitating activity of both polysaccharides. N-acetyl-mannosamine-6-phosphate inhibited the precipitation reaction between strain Sh-17 and meningococcal group A antisera. Only mannosamine phosphate was detected in trichloroacetic acid extracts of Sh-17 polysaccharide and meningococcal group A antigen-antibody precipitates.

Binding properties of immunoglobulin combining sites specific for terminal or nonterminal antigenic determinants in dextran

Binding constants of the dextran-reactive BALB/c mouse IgA myeloma proteins W3129 and QUPC 52 have been determined for each member of the isomaltose series of oligosaccharides and for methyl alphaDglucoside. Protein W3129 has maximum complementarity for isomaltopentaose (IM5) deltaf degrees = 7,180 cal/mol) with 55-60% of the total binding energy directed against methylalphaDglucoside. Protein QUPC 52 gives maximum binding with isomaltohexaose (IM6) (deltaF degrees = -5,340 cal/mol) and has about 70% of its total binding energy for isomaltotriose (IM3), but at most only 5% for isomaltose (IM2) or methyl alphaDglucoside. Protein W3129 precipitates with branched dextrans high in alpha (1 yields 6) linkages and reacts with but does not precipitate a synthetic alpha (1 yields 6)-linked linear dextran. Protein QUPC 52 precipitates both branched and linear dextrans. Thus, the immunodominant group for protein W3129 is mimicked by methyl alphaDglucoside and this protein reacts exclusively at the terminal nonreducing ends of alpha (1 yields 6)-linked dextran chains. Protein QUPC 52 has an immunodominant group which is expressed by IM3 but not smaller oligosaccharides and this protein can react at nonterminal locations along alpha (1 yields 6)-linked dextran chains. Precipitation of linear dextran seems to be a valid although not quantitative assay for antidextrans with nonterminal specificity. Quantitative precipitin reactions with branched and linear dextrans suggest that alpha (1 yields 6)-specific human antidextrans are mixtures of molecules having terminal and nonterminal specificities and that the fraction of each type can vary among individuals. Rabbit antisera against IM3 or IM6 coupled to bovine serum albumin also appear to contain antibodies with nonterminal specificity for dextran chains although a large fraction has terminal specificity. Low molecular weight clinical dextran N-150N (congruent to 60,000) reacted more like linear dextran than like its parent native-branched dextran B512. This is thought to result from an abundance of nonterminal determinants in clinical dextran N-150N but a very small number of functional terminal determinants per molecule. An appreciation of terminal and nonterminal specificities and of the different immunodominant structures in isomaltosyl chains has proven to be of a great value in understanding the immunochemical reactions of dextrans. Moreover, certain previous findings with fructosan-reactive mouse myeloma proteins and human antilevans (55, 84) also suggest terminal and nonterminal specificities for levan chains.

Immunological properties of teichoic acids

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The wall teichoic acids of Lactobacillus plantarum N.I.R.D.C106. Location of the phosphodiester groups and separation of the chains

1. The identities of the component glycerol glucosides of the wall teichoic acids of Lactobacillus plantarum N.I.R.D. C106 have been confirmed by methylation analysis. These glucosides are alpha-d-glucopyranosyl-(1-->1)-l-glycerol, alpha-d-glucopyranosyl-(1-->2)-alpha-d-glucopyranosyl-(1-->1)-l-glycerol and alpha-d-glucopyranosyl-(1-->3)-alpha-d-glucopyranosyl-(1-->1)-l-glycerol. 2. These units are connected by phosphodiester groups attached to the 3(l)-hydroxyl group of glycerol and the 6-hydroxyl group of the non-reducing terminal glucose residues in the adjacent unit. 3. Concanavalin A forms a precipitate with the teichoic acid and the material so precipitated contains only the alpha-d-glucopyranosyl-(1-->2)-alpha-d-glucopyranosyl -(1-->1)-l-glycerol component. This unit is therefore present in a homogeneous polymer so that the teichoic acid is a mixture of this and of other possibly homogeneous chains containing the other two components.

'False positive' precipitation reactions to extracts of organic dusts due to a teichoic acid from S. aureus. Techniques

Precipitation reactions regarded as `false positive' have been obtained to extracts of a variety of organic dusts. The antigen responsible for these reactions is an electrophoretically fast moving and negatively charged substance, previously observed in extracts of mouldy hay and other vegetable and organic dusts, and referred to as a `D line' antigen. This antigen has now been shown to have antigenic determinants in common with a β-teichoic acid prepared from Staphylococcus aureus . Absorption of the sera with N -acetyl-D-glucosamine had an inhibitory effect on `D line' and teichoic acid precipitin reactions.

Prevention of staphylococcal bacteriophage activity by antigen A precipitins in human sera

Antigen A precipitins in human sera prevented plaque formation and propagation of staphylococcal bacteriophages. Over 20% of total IgG was removed from human sera by absorption with staphylococci containing antigen A. The specific precipitating antibody in rabbit antisera formed lines of idenity with antigen A precipitins in lower dilutions of human sera but formed lines of nonidenity with antigen A precipitins in higher dilutions of the same sera, suggesting both specific and nonspecific antigen A precipitins in human sera. The specific and nonspecific antigen A precipitins in human sera may prevent the in vivo activity of staphylococcal bacteriophages which have been demonstrated previously in animals whose sera do not contain either specific or nonspecific antigen A precipitins.

Studies on human antibodies. VI. Selective variations in subgroup composition and genetic markers

The composition of various isolated antibodies was determined by quantitative analyses for heavy chain subgroups and light chain types. Certain antibodies such as anti-tetanus toxoid and anti-A isoagglutinins were predominantly of the major gammaG1-type. However, a high preponderance of molecules of the minor gammaG2-subgroup was found for antibodies to dextran, levan, and teichoic acid. These findings explain some unusual features previously noted for anti-dextrans such as weak PCA reactions and lack of Gm antigens. Studies of several isolated antibodies from single heterozygous individuals showed a selective absence of genetic markers in certain antibodies and their presence in others. The "allelic exclusion" principle was clearly evident in the isolated antibodies of two different individuals. Large differences in the ratio of kappa to lambda light chains were observed for the same type of antibody from different individuals. Subfractionation of dextran antibodies by affinity for specific glycosidic linkage or combining site size produced marked changes in the ratios. The isomaltohexaose eluates of the dextran antibodies from two subjects were primarily kappa and the isomaltotriose eluates were predominantly lambda. The one anti-levan antibody studied was uniquely homogeneous, consisting exclusively of gammaG2-heavy chains and kappa light chains. By these criteria as well as others, it closely resembled myeloma proteins.

Serological activity of staphylococcal polysaccharide

The polysaccharide from cell walls of coagulase-positive staphylococci coated both latex particles and tanned red cells for agglutination by human sera and by specific staphylococcal antisera. Treatment with trypsin or autoclaving destroyed the capacity of polysaccharide to coat particles but did not affect precipitation of antibody. Periodic acid destroyed both properties. The teichoic acid portion of the staphylococcal polysaccharide displayed precipitin activity similar to polysaccharide, but it did not coat either latex particles or tanned red cells. Teichoic acid did, however, inhibit specific agglutination of polysaccharide-coated particles or cells.